Android中将xml布局文件转化为View树的过程分析（上）

　　有好几周没写东西了，一方面是因为前几个周末都有些事情，另外也是因为没能找到好的写作方向，或者说有些话题

值得分享、写作，可是自己积累还不够，没办法只好闷头继续研究了。这段时间一边在写代码，一边也在想Android中

究竟是如何将R.layout.xxx_view.xml这样的布局文件加载到Android系统的view层次结构中的（即我们常说的view树）。

这期间一方面自己研究了下源码，另一方面也在网上搜索了下相关文章，发现了2篇很不错的同主题文章，推荐给大家：

http://blog.csdn.net/qinjuning/article/details/7226787&http://blog.csdn.net/bigconvience/article/details/28626631。

　　我们在开发中接触最早的应该算是Activity.setContentView(int resourceId)方法了，我们知道在Activity的onCreate中调用此

方法可以把我们提供的根布局文件加载到activity中并显示出来。很自然地我们就从它开始说起吧，废话不多说上代码：

    /**     * Set the activity content from a layout resource.  The resource will be     * inflated, adding all top-level views to the activity.     *     * @param layoutResID Resource ID to be inflated.     *      * @see #setContentView(android.view.View)     * @see #setContentView(android.view.View, android.view.ViewGroup.LayoutParams)     */    public void setContentView(int layoutResID) { // 实际上其内部都是delegate给了getWindow()方法        getWindow().setContentView(layoutResID);        initActionBar();    }    /**     * Set the activity content to an explicit view.  This view is placed     * directly into the activity's view hierarchy.  It can itself be a complex     * view hierarchy.  When calling this method, the layout parameters of the     * specified view are ignored.  Both the width and the height of the view are     * set by default to {@link ViewGroup.LayoutParams#MATCH_PARENT}. To use     * your own layout parameters, invoke     * {@link #setContentView(android.view.View, android.view.ViewGroup.LayoutParams)}     * instead.     *      * @param view The desired content to display.     *     * @see #setContentView(int)     * @see #setContentView(android.view.View, android.view.ViewGroup.LayoutParams)     */    public void setContentView(View view) {        getWindow().setContentView(view);        initActionBar();    }    /**     * Set the activity content to an explicit view.  This view is placed     * directly into the activity's view hierarchy.  It can itself be a complex     * view hierarchy.     *      * @param view The desired content to display.     * @param params Layout parameters for the view.     *     * @see #setContentView(android.view.View)     * @see #setContentView(int)     */    public void setContentView(View view, ViewGroup.LayoutParams params) {        getWindow().setContentView(view, params);        initActionBar();    }    /**     * Add an additional content view to the activity.  Added after any existing     * ones in the activity -- existing views are NOT removed.     *      * @param view The desired content to display.     * @param params Layout parameters for the view.     */    public void addContentView(View view, ViewGroup.LayoutParams params) {        getWindow().addContentView(view, params);        initActionBar();    }

我们可以看到setContentView方法内部都delegate给了getWindow()方法，这里顺便也把addContentView提及了下，setXXX有

替换的意思，addXXX则是往后面在加一个，即以前的还在。紧接着我们看下Activity里的window是咋来的吧，代码如下：

    private Window mWindow; // Activity的一个字段

    /**     * Retrieve the current {@link android.view.Window} for the activity.     * This can be used to directly access parts of the Window API that     * are not available through Activity/Screen.     *      * @return Window The current window, or null if the activity is not     *         visual.     */    public Window getWindow() {        return mWindow;    }    final void attach(Context context, ActivityThread aThread, Instrumentation instr, IBinder token,            Application application, Intent intent, ActivityInfo info, CharSequence title,             Activity parent, String id, NonConfigurationInstances lastNonConfigurationInstances,            Configuration config) {        attach(context, aThread, instr, token, 0, application, intent, info, title, parent, id,            lastNonConfigurationInstances, config);    }        final void attach(Context context, ActivityThread aThread,            Instrumentation instr, IBinder token, int ident,            Application application, Intent intent, ActivityInfo info,            CharSequence title, Activity parent, String id,            NonConfigurationInstances lastNonConfigurationInstances,            Configuration config) {        attachBaseContext(context);        mFragments.attachActivity(this, mContainer, null);                mWindow = PolicyManager.makeNewWindow(this); // 注意这行代码，这里实际上创建了一个PhoneWindow的实例        mWindow.setCallback(this); // window对象里的Callback接口的实现是Activity        mWindow.getLayoutInflater().setPrivateFactory(this);        if (info.softInputMode != WindowManager.LayoutParams.SOFT_INPUT_STATE_UNSPECIFIED) {            mWindow.setSoftInputMode(info.softInputMode);        }        if (info.uiOptions != 0) {            mWindow.setUiOptions(info.uiOptions);        }        mUiThread = Thread.currentThread();                mMainThread = aThread;        mInstrumentation = instr;        mToken = token;        mIdent = ident;        mApplication = application;        mIntent = intent;        mComponent = intent.getComponent();        mActivityInfo = info;        mTitle = title;        mParent = parent;        mEmbeddedID = id;        mLastNonConfigurationInstances = lastNonConfigurationInstances;        mWindow.setWindowManager(                (WindowManager)context.getSystemService(Context.WINDOW_SERVICE),                mToken, mComponent.flattenToString(),                (info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);        if (mParent != null) {            mWindow.setContainer(mParent.getWindow());        }        mWindowManager = mWindow.getWindowManager();        mCurrentConfig = config;    }

从代码我们可以看出是在Activity.attach方法中对mWindow进行初始化的，这里也顺便解释下Window、Activity、View的区别和联系：

Window是个封装了窗体样式和行为的策略抽象类，它的实例作为顶层view被加到window manager里面；它提供了标准的UI策略，

如背景、标题栏、默认的key处理逻辑等等。在Android系统中有一个唯一的实现PhoneWindow，当我们需要window的

时候就会有一个PhoneWindow的实例被new出来。每个Activity都有一个与之关联的window对象，Activity在其上绘制UI。

Window对象里又有一个mDecor对象，它是window里的顶层view（也就是说view树的层次结构从它开始，它是view树的根）。

更多的解释可以参考这个问题：http://stackoverflow.com/questions/9451755/what-is-an-android-window。

　　接着我们看看上面代码里具体给mWindow对象赋值的代码，先来看看com.android.internal.policy.PolicyManager类：

    public final class PolicyManager {    private static final String POLICY_IMPL_CLASS_NAME =        "com.android.internal.policy.impl.Policy";    private static final IPolicy sPolicy;    static {        // Pull in the actual implementation of the policy at run-time        try {            Class policyClass = Class.forName(POLICY_IMPL_CLASS_NAME); // 加载class文件            sPolicy = (IPolicy)policyClass.newInstance(); // 根据Class对象，创建个实例        } catch (ClassNotFoundException ex) {            throw new RuntimeException(                    POLICY_IMPL_CLASS_NAME + " could not be loaded", ex);        } catch (InstantiationException ex) {            throw new RuntimeException(                    POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);        } catch (IllegalAccessException ex) {            throw new RuntimeException(                    POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);        }    }    // Cannot instantiate this class    private PolicyManager() {}    // The static methods to spawn new policy-specific objects    public static Window makeNewWindow(Context context) {        return sPolicy.makeNewWindow(context);    }    public static LayoutInflater makeNewLayoutInflater(Context context) {        return sPolicy.makeNewLayoutInflater(context);    }    public static WindowManagerPolicy makeNewWindowManager() {        return sPolicy.makeNewWindowManager();    }    public static FallbackEventHandler makeNewFallbackEventHandler(Context context) {        return sPolicy.makeNewFallbackEventHandler(context);    }}

接着我们看下sPolicy的具体实现类，com.android.internal.policy.impl.Policy.java文件：

public class Policy implements IPolicy {    private static final String TAG = "PhonePolicy";    private static final String[] preload_classes = {        "com.android.internal.policy.impl.PhoneLayoutInflater",        "com.android.internal.policy.impl.PhoneWindow",        "com.android.internal.policy.impl.PhoneWindow$1",        "com.android.internal.policy.impl.PhoneWindow$DialogMenuCallback",        "com.android.internal.policy.impl.PhoneWindow$DecorView",        "com.android.internal.policy.impl.PhoneWindow$PanelFeatureState",        "com.android.internal.policy.impl.PhoneWindow$PanelFeatureState$SavedState",    };    static {        // For performance reasons, preload some policy specific classes when        // the policy gets loaded.        for (String s : preload_classes) {            try {                Class.forName(s); // 预加载这些类的class文件，以便后面new他们的对象            } catch (ClassNotFoundException ex) {                Log.e(TAG, "Could not preload class for phone policy: " + s);            }        }    }    public Window makeNewWindow(Context context) {        return new PhoneWindow(context); // 至此我们看到了Android系统里真正且唯一的Window类型，PhoneWindow    }    public LayoutInflater makeNewLayoutInflater(Context context) {        return new PhoneLayoutInflater(context); // LayoutInflater接口的实际实现者，以后我们的代码里出现的类似    }                               // (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE)                                    // 这样的代码，返回的都是此对象。    public WindowManagerPolicy makeNewWindowManager() {        return new PhoneWindowManager();    }    public FallbackEventHandler makeNewFallbackEventHandler(Context context) {        return new PhoneFallbackEventHandler(context);    }}

至此我们看清楚了Activity中的mWindow对象实际上是PhoneWindow的实例。搞清楚了window对象咋来的，接下来我们可以

分析其setContentView方法了，代码如下：

    // This is the top-level view of the window, containing the window decor.    private DecorView mDecor; // window中的顶层view    // This is the view in which the window contents are placed. It is either    // mDecor itself, or a child of mDecor where the contents go.    private ViewGroup mContentParent; // Android为我们提供的window布局文件中[email protected]:id/content的view                                      // 后面我们会看几个典型的window布局文件    private LayoutInflater mLayoutInflater;    public PhoneWindow(Context context) {        super(context);        mLayoutInflater = LayoutInflater.from(context); // 我们在上文中提到的通过context.getSystemService实现    }    @Override    public void setContentView(int layoutResID) {        if (mContentParent == null) { // 第一次调用的时候执行            installDecor();                   } else { // 可以看出setContentView支持多次调用，只是相当于把之前的view层次结构扔掉，从头再来而已            mContentParent.removeAllViews();        }        mLayoutInflater.inflate(layoutResID, mContentParent); // 将我们dev提供的顶层layout文件加到mContentParent里面        final Callback cb = getCallback();        if (cb != null && !isDestroyed()) {            cb.onContentChanged(); // 调用回调函数，一般是Activity或Dialog        }    }    @Override    public void setContentView(View view) { // 默认的LayoutParams是MATCH_PARENT，当然你也可以指定        setContentView(view, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));    }    @Override    public void setContentView(View view, ViewGroup.LayoutParams params) {        if (mContentParent == null) {            installDecor();        } else {            mContentParent.removeAllViews();        }        mContentParent.addView(view, params);        final Callback cb = getCallback();        if (cb != null && !isDestroyed()) {            cb.onContentChanged();        }    }    @Override    public void addContentView(View view, ViewGroup.LayoutParams params) {        if (mContentParent == null) {             installDecor();        } // 注意相比setContentView来说，少了mContentParent.removeAllViews()调用，
          // 所以效果就是之前的view层次结构还在，只是新增了一个view        mContentParent.addView(view, params);        final Callback cb = getCallback();        if (cb != null && !isDestroyed()) {            cb.onContentChanged();        }    }

接着我们看看installDecor相关的实现：

    private void installDecor() {        if (mDecor == null) {            mDecor = generateDecor(); // new一个DecorView（一种特殊的FrameLayout）            mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);            mDecor.setIsRootNamespace(true);            if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {                mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);            }        }        if (mContentParent == null) {            mContentParent = generateLayout(mDecor); // 初始化mContentParent            // Set up decor part of UI to ignore fitsSystemWindows if appropriate.            mDecor.makeOptionalFitsSystemWindows();            mTitleView = (TextView)findViewById(com.android.internal.R.id.title);            if (mTitleView != null) {                mTitleView.setLayoutDirection(mDecor.getLayoutDirection());                if ((getLocalFeatures() & (1 << FEATURE_NO_TITLE)) != 0) {                    View titleContainer = findViewById(com.android.internal.R.id.title_container);                    if (titleContainer != null) {                        titleContainer.setVisibility(View.GONE);                    } else {                        mTitleView.setVisibility(View.GONE);                    }                    if (mContentParent instanceof FrameLayout) {                        ((FrameLayout)mContentParent).setForeground(null);                    }                } else {                    mTitleView.setText(mTitle);                }            } else {                mActionBar = (ActionBarView) findViewById(com.android.internal.R.id.action_bar);                if (mActionBar != null) {                    mActionBar.setWindowCallback(getCallback());                    if (mActionBar.getTitle() == null) {                        mActionBar.setWindowTitle(mTitle);                    }                    final int localFeatures = getLocalFeatures();                    if ((localFeatures & (1 << FEATURE_PROGRESS)) != 0) {                        mActionBar.initProgress();                    }                    if ((localFeatures & (1 << FEATURE_INDETERMINATE_PROGRESS)) != 0) {                        mActionBar.initIndeterminateProgress();                    }                    final ActionBarOverlayLayout abol = (ActionBarOverlayLayout) findViewById(                            com.android.internal.R.id.action_bar_overlay_layout);                    if (abol != null) {                        abol.setOverlayMode(                                (localFeatures & (1 << FEATURE_ACTION_BAR_OVERLAY)) != 0);                    }                    boolean splitActionBar = false;                    final boolean splitWhenNarrow =                            (mUiOptions & ActivityInfo.UIOPTION_SPLIT_ACTION_BAR_WHEN_NARROW) != 0;                    if (splitWhenNarrow) {                        splitActionBar = getContext().getResources().getBoolean(                                com.android.internal.R.bool.split_action_bar_is_narrow);                    } else {                        splitActionBar = getWindowStyle().getBoolean(                                com.android.internal.R.styleable.Window_windowSplitActionBar, false);                    }                    final ActionBarContainer splitView = (ActionBarContainer) findViewById(                            com.android.internal.R.id.split_action_bar);                    if (splitView != null) {                        mActionBar.setSplitView(splitView);                        mActionBar.setSplitActionBar(splitActionBar);                        mActionBar.setSplitWhenNarrow(splitWhenNarrow);                        final ActionBarContextView cab = (ActionBarContextView) findViewById(                                com.android.internal.R.id.action_context_bar);                        cab.setSplitView(splitView);                        cab.setSplitActionBar(splitActionBar);                        cab.setSplitWhenNarrow(splitWhenNarrow);                    } else if (splitActionBar) {                        Log.e(TAG, "Requested split action bar with " +                                "incompatible window decor! Ignoring request.");                    }                    if ((mResourcesSetFlags & FLAG_RESOURCE_SET_ICON) != 0 ||                            (mIconRes != 0 && !mActionBar.hasIcon())) {                        mActionBar.setIcon(mIconRes);                    } else if ((mResourcesSetFlags & FLAG_RESOURCE_SET_ICON) == 0 &&                            mIconRes == 0 && !mActionBar.hasIcon()) {                        mActionBar.setIcon(                                getContext().getPackageManager().getDefaultActivityIcon());                        mResourcesSetFlags |= FLAG_RESOURCE_SET_ICON_FALLBACK;                    }                    if ((mResourcesSetFlags & FLAG_RESOURCE_SET_LOGO) != 0 ||                            (mLogoRes != 0 && !mActionBar.hasLogo())) {                        mActionBar.setLogo(mLogoRes);                    }                    // Post the panel invalidate for later; avoid application onCreateOptionsMenu                    // being called in the middle of onCreate or similar.                    mDecor.post(new Runnable() {                        public void run() {                            // Invalidate if the panel menu hasn't been created before this.                            PanelFeatureState st = getPanelState(FEATURE_OPTIONS_PANEL, false);                            if (!isDestroyed() && (st == null || st.menu == null)) {                                invalidatePanelMenu(FEATURE_ACTION_BAR);                            }                        }                    });                }            }        }    }    protected DecorView generateDecor() { // 我会在合适的时候专门分析下DecorView        return new DecorView(getContext(), -1);    }    protected ViewGroup generateLayout(DecorView decor) {        // Apply data from current theme.        TypedArray a = getWindowStyle();        if (false) {            System.out.println("From style:");            String s = "Attrs:";            for (int i = 0; i < com.android.internal.R.styleable.Window.length; i++) {                s = s + " " + Integer.toHexString(com.android.internal.R.styleable.Window[i]) + "="                        + a.getString(i);            }            System.out.println(s);        }        // 接下来的一大堆代码都是从window的theme中获取属性值，然后调用相应的requestFeature或setFlags方法        mIsFloating = a.getBoolean(com.android.internal.R.styleable.Window_windowIsFloating, false);        int flagsToUpdate = (FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR)                & (~getForcedWindowFlags());        if (mIsFloating) { // 比如这里，如果是floating的（如dialog），则设置layout为WRAP_CONTENT，即非全屏            setLayout(WRAP_CONTENT, WRAP_CONTENT);            setFlags(0, flagsToUpdate);        } else {            setFlags(FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR, flagsToUpdate);        }        if (a.getBoolean(com.android.internal.R.styleable.Window_windowNoTitle, false)) {            requestFeature(FEATURE_NO_TITLE);        } else if (a.getBoolean(com.android.internal.R.styleable.Window_windowActionBar, false)) {            // Don't allow an action bar if there is no title.            requestFeature(FEATURE_ACTION_BAR);        }        if (a.getBoolean(com.android.internal.R.styleable.Window_windowActionBarOverlay, false)) {            requestFeature(FEATURE_ACTION_BAR_OVERLAY);        }        if (a.getBoolean(com.android.internal.R.styleable.Window_windowActionModeOverlay, false)) {            requestFeature(FEATURE_ACTION_MODE_OVERLAY);        }        if (a.getBoolean(com.android.internal.R.styleable.Window_windowFullscreen, false)) {            setFlags(FLAG_FULLSCREEN, FLAG_FULLSCREEN & (~getForcedWindowFlags()));        }        if (a.getBoolean(com.android.internal.R.styleable.Window_windowTranslucentStatus,                false)) {            setFlags(FLAG_TRANSLUCENT_STATUS, FLAG_TRANSLUCENT_STATUS                    & (~getForcedWindowFlags()));        }        if (a.getBoolean(com.android.internal.R.styleable.Window_windowTranslucentNavigation,                false)) {            setFlags(FLAG_TRANSLUCENT_NAVIGATION, FLAG_TRANSLUCENT_NAVIGATION                    & (~getForcedWindowFlags()));        }        if (a.getBoolean(com.android.internal.R.styleable.Window_windowOverscan, false)) {            setFlags(FLAG_LAYOUT_IN_OVERSCAN, FLAG_LAYOUT_IN_OVERSCAN&(~getForcedWindowFlags()));        }        if (a.getBoolean(com.android.internal.R.styleable.Window_windowShowWallpaper, false)) {            setFlags(FLAG_SHOW_WALLPAPER, FLAG_SHOW_WALLPAPER&(~getForcedWindowFlags()));        }        if (a.getBoolean(com.android.internal.R.styleable.Window_windowEnableSplitTouch,                getContext().getApplicationInfo().targetSdkVersion                        >= android.os.Build.VERSION_CODES.HONEYCOMB)) {            setFlags(FLAG_SPLIT_TOUCH, FLAG_SPLIT_TOUCH&(~getForcedWindowFlags()));        }        a.getValue(com.android.internal.R.styleable.Window_windowMinWidthMajor, mMinWidthMajor);        a.getValue(com.android.internal.R.styleable.Window_windowMinWidthMinor, mMinWidthMinor);        if (a.hasValue(com.android.internal.R.styleable.Window_windowFixedWidthMajor)) {            if (mFixedWidthMajor == null) mFixedWidthMajor = new TypedValue();            a.getValue(com.android.internal.R.styleable.Window_windowFixedWidthMajor,                    mFixedWidthMajor);        }        if (a.hasValue(com.android.internal.R.styleable.Window_windowFixedWidthMinor)) {            if (mFixedWidthMinor == null) mFixedWidthMinor = new TypedValue();            a.getValue(com.android.internal.R.styleable.Window_windowFixedWidthMinor,                    mFixedWidthMinor);        }        if (a.hasValue(com.android.internal.R.styleable.Window_windowFixedHeightMajor)) {            if (mFixedHeightMajor == null) mFixedHeightMajor = new TypedValue();            a.getValue(com.android.internal.R.styleable.Window_windowFixedHeightMajor,                    mFixedHeightMajor);        }        if (a.hasValue(com.android.internal.R.styleable.Window_windowFixedHeightMinor)) {            if (mFixedHeightMinor == null) mFixedHeightMinor = new TypedValue();            a.getValue(com.android.internal.R.styleable.Window_windowFixedHeightMinor,                    mFixedHeightMinor);        }        final Context context = getContext();        final int targetSdk = context.getApplicationInfo().targetSdkVersion;        final boolean targetPreHoneycomb = targetSdk < android.os.Build.VERSION_CODES.HONEYCOMB;        final boolean targetPreIcs = targetSdk < android.os.Build.VERSION_CODES.ICE_CREAM_SANDWICH;        final boolean targetHcNeedsOptions = context.getResources().getBoolean(                com.android.internal.R.bool.target_honeycomb_needs_options_menu);        final boolean noActionBar = !hasFeature(FEATURE_ACTION_BAR) || hasFeature(FEATURE_NO_TITLE);        if (targetPreHoneycomb || (targetPreIcs && targetHcNeedsOptions && noActionBar)) {            addFlags(WindowManager.LayoutParams.FLAG_NEEDS_MENU_KEY);        } else {            clearFlags(WindowManager.LayoutParams.FLAG_NEEDS_MENU_KEY);        }                if (mAlwaysReadCloseOnTouchAttr || getContext().getApplicationInfo().targetSdkVersion                >= android.os.Build.VERSION_CODES.HONEYCOMB) {            if (a.getBoolean(                    com.android.internal.R.styleable.Window_windowCloseOnTouchOutside,                    false)) {                setCloseOnTouchOutsideIfNotSet(true);            }        }                WindowManager.LayoutParams params = getAttributes();        if (!hasSoftInputMode()) {            params.softInputMode = a.getInt(                    com.android.internal.R.styleable.Window_windowSoftInputMode,                    params.softInputMode);        }        if (a.getBoolean(com.android.internal.R.styleable.Window_backgroundDimEnabled,                mIsFloating)) {            /* All dialogs should have the window dimmed */            if ((getForcedWindowFlags()&WindowManager.LayoutParams.FLAG_DIM_BEHIND) == 0) {                params.flags |= WindowManager.LayoutParams.FLAG_DIM_BEHIND;            }            if (!haveDimAmount()) {                params.dimAmount = a.getFloat(                        android.R.styleable.Window_backgroundDimAmount, 0.5f);            }        }        if (params.windowAnimations == 0) {            params.windowAnimations = a.getResourceId(                    com.android.internal.R.styleable.Window_windowAnimationStyle, 0);        }        // The rest are only done if this window is not embedded; otherwise,        // the values are inherited from our container.        if (getContainer() == null) {            if (mBackgroundDrawable == null) {                if (mBackgroundResource == 0) {                    mBackgroundResource = a.getResourceId(                            com.android.internal.R.styleable.Window_windowBackground, 0);                }                if (mFrameResource == 0) {                    mFrameResource = a.getResourceId(com.android.internal.R.styleable.Window_windowFrame, 0);                }                if (false) {                    System.out.println("Background: "                            + Integer.toHexString(mBackgroundResource) + " Frame: "                            + Integer.toHexString(mFrameResource));                }            }            mTextColor = a.getColor(com.android.internal.R.styleable.Window_textColor, 0xFF000000);        }        // Inflate the window decor.        // 接下来就是根据设定好的features（即窗口风格属性）选择对应的xml文件        int layoutResource;        int features = getLocalFeatures();        // System.out.println("Features: 0x" + Integer.toHexString(features));        if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) {            if (mIsFloating) {                TypedValue res = new TypedValue();                getContext().getTheme().resolveAttribute(                        com.android.internal.R.attr.dialogTitleIconsDecorLayout, res, true);                layoutResource = res.resourceId;            } else {                layoutResource = com.android.internal.R.layout.screen_title_icons;            }            // XXX Remove this once action bar supports these features.            removeFeature(FEATURE_ACTION_BAR);            // System.out.println("Title Icons!");        } else if ((features & ((1 << FEATURE_PROGRESS) | (1 << FEATURE_INDETERMINATE_PROGRESS))) != 0                && (features & (1 << FEATURE_ACTION_BAR)) == 0) {            // Special case for a window with only a progress bar (and title).            // XXX Need to have a no-title version of embedded windows.            layoutResource = com.android.internal.R.layout.screen_progress;            // System.out.println("Progress!");        } else if ((features & (1 << FEATURE_CUSTOM_TITLE)) != 0) {            // Special case for a window with a custom title.            // If the window is floating, we need a dialog layout            if (mIsFloating) {                TypedValue res = new TypedValue();                getContext().getTheme().resolveAttribute(                        com.android.internal.R.attr.dialogCustomTitleDecorLayout, res, true);                layoutResource = res.resourceId;            } else {                layoutResource = com.android.internal.R.layout.screen_custom_title;            }            // XXX Remove this once action bar supports these features.            removeFeature(FEATURE_ACTION_BAR);        } else if ((features & (1 << FEATURE_NO_TITLE)) == 0) {            // If no other features and not embedded, only need a title.            // If the window is floating, we need a dialog layout            if (mIsFloating) {                TypedValue res = new TypedValue();                getContext().getTheme().resolveAttribute(                        com.android.internal.R.attr.dialogTitleDecorLayout, res, true);                layoutResource = res.resourceId;            } else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) {                layoutResource = com.android.internal.R.layout.screen_action_bar;            } else {                layoutResource = com.android.internal.R.layout.screen_title;            }            // System.out.println("Title!");        } else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) {            layoutResource = com.android.internal.R.layout.screen_simple_overlay_action_mode;        } else {            // Embedded, so no decoration is needed.            layoutResource = com.android.internal.R.layout.screen_simple;            // System.out.println("Simple!");        }        mDecor.startChanging(); // 回调点，表示开始。。。        View in = mLayoutInflater.inflate(layoutResource, null); // 将选定的layout文件inflate成view        decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT)); // 将其添加到decor中        ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT); // 找到系统layout文件中为我们客户端布局预留        if (contentParent == null) {                                     // 的placeholder，我们的Activity布局将从这里开始。            throw new RuntimeException("Window couldn't find content container view");        }        if ((features & (1 << FEATURE_INDETERMINATE_PROGRESS)) != 0) {            ProgressBar progress = getCircularProgressBar(false);            if (progress != null) {                progress.setIndeterminate(true);            }        }        // Remaining setup -- of background and title -- that only applies        // to top-level windows.        if (getContainer() == null) {            Drawable drawable = mBackgroundDrawable;            if (mBackgroundResource != 0) {                drawable = getContext().getResources().getDrawable(mBackgroundResource);            }            mDecor.setWindowBackground(drawable);            drawable = null;            if (mFrameResource != 0) {                drawable = getContext().getResources().getDrawable(mFrameResource);            }            mDecor.setWindowFrame(drawable);            // System.out.println("Text=" + Integer.toHexString(mTextColor) +            // " Sel=" + Integer.toHexString(mTextSelectedColor) +            // " Title=" + Integer.toHexString(mTitleColor));            if (mTitleColor == 0) {                mTitleColor = mTextColor;            }            if (mTitle != null) {                setTitle(mTitle);            }            setTitleColor(mTitleColor);        }        mDecor.finishChanging(); // 回调点，表示结束了。。。        return contentParent; // 返回客户端（Activity）布局的parent view    }

mContentParent被正确初始化后，在setContentView中通过mLayoutInflater.inflate(layoutResID, mContentParent);

这样的代码就可以将Activity的布局文件加到整个view层次结构中，这样我们的layout xml就和系统的联系起来了。

　　下面我们看几个前面说到的系统提供的布局文件，针对某个特定的feature属性，代码如下：

<!-- screen_title.xml --><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical"    android:fitsSystemWindows="true">    <!-- Popout bar for action modes -->    <ViewStub android:id="@+id/action_mode_bar_stub"              android:inflatedId="@+id/action_mode_bar"              android:layout="@layout/action_mode_bar"              android:layout_width="match_parent"              android:layout_height="wrap_content" />    <FrameLayout        android:layout_width="match_parent"         android:layout_height="?android:attr/windowTitleSize"        style="?android:attr/windowTitleBackgroundStyle">        <TextView android:id="@android:id/title"             style="?android:attr/windowTitleStyle"            android:background="@null"            android:fadingEdge="horizontal"            android:gravity="center_vertical"            android:layout_width="match_parent"            android:layout_height="match_parent" />    </FrameLayout>    <FrameLayout android:id="@android:id/content" // 注意这里的共同点，这就是给客户端程序预留的placeholder，mContentParent view        android:layout_width="match_parent"         android:layout_height="0dip"        android:layout_weight="1"        android:foregroundGravity="fill_horizontal|top"        android:foreground="?android:attr/windowContentOverlay" /></LinearLayout><!-- screen_simple.xml --><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:fitsSystemWindows="true"    android:orientation="vertical">    <ViewStub android:id="@+id/action_mode_bar_stub"              android:inflatedId="@+id/action_mode_bar"              android:layout="@layout/action_mode_bar"              android:layout_width="match_parent"              android:layout_height="wrap_content" />    <FrameLayout         android:id="@android:id/content" // 共同点，id都是android:id/content         android:layout_width="match_parent"         android:layout_height="match_parent"         android:foregroundInsidePadding="false"         android:foregroundGravity="fill_horizontal|top"         android:foreground="?android:attr/windowContentOverlay" /></LinearLayout>

　　在我们的开发中，还经常会使用LayoutInflater.inflate方法来将某一个xml文件动态添加到view层次结构中，这种方式简直太棒了。

当然为了避免篇幅过长，我会在下一篇文章中专门分析下这种情况，敬请期待。终于可以收工了，准备看西班牙-荷兰的比赛了，哈哈。。。

更多相关文章

随机推荐