UI控件

ViewGroup

ViewGroup实现了ViewManager和ViewParent两个接口。

@UiThreadpublic abstract class ViewGroup extends View implements ViewParent, ViewManager {

ViewManager

public interface ViewManager {    public void addView(View view, ViewGroup.LayoutParams params);    public void updateViewLayout(View view, ViewGroup.LayoutParams params);    public void removeView(View view);}

在inflate的过程中，主要用到的是构造和addView。第一个View参数不用说了，要加入的子View。另外一个重要的参数是ViewGroup.LayoutParams. 这个参数的主要用途是指定子View的位置。

ViewGroup.LayoutParams

ViewGroup.LayoutParams的基本属性

作为一个基本类，它的主要作用是指定子View的宽和高。
除了直接指定大小之外，它还接受两个值：MATCH_PARENT（老的名字叫FILL_PARENT）和WRAP_CONTENT. 这大家都太熟悉了，就不多说了。

下面抽象一下，常量和宽高，是我们熟悉的部分。

6770    public static class LayoutParams {...6777        @SuppressWarnings({"UnusedDeclaration"})6778        @Deprecated6779        public static final int FILL_PARENT = -1;...6786        public static final int MATCH_PARENT = -1;...6793        public static final int WRAP_CONTENT = -2;...6804        public int width;6815        public int height;

下面是布局动画的，先放在这里，用到再说。

        /** * Used to animate layouts. */        public LayoutAnimationController.AnimationParameters layoutAnimationParameters;

ViewGroup.LayoutParams的构造方法

别看下面都是又是主题，又是绕来绕去的高大上方法。本质上，ViewGroup.LayoutParams就是宽和高两个域。这两个值赋正确了，其它的就都不用管。值可以是具体的pixel值，也可以是MATCH_PARENT或者WRAP_CONTENT两个常量。

我们把代码中的几个构造方法的顺序调整一下，先看说人话的。
第一个是最正宗的赋值型构造，两个值一赋就OK。

public LayoutParams(int width, int height) {    this.width = width;    this.height = height;}

再看下拷贝构造方法：

/** * Copy constructor. Clones the width and height values of the source. * * @param source The layout params to copy from. */public LayoutParams(LayoutParams source) {    this.width = source.width;    this.height = source.height;}

然后再看说文言的，这个得转几道手，看几个其它类的方法：

6840        public LayoutParams(Context c, AttributeSet attrs) {6841            TypedArray a = c.obtainStyledAttributes(attrs, R.styleable.ViewGroup_Layout);6842            setBaseAttributes(a,6843                    R.styleable.ViewGroup_Layout_layout_width,6844                    R.styleable.ViewGroup_Layout_layout_height);6845            a.recycle();6846        }

首先来看这个Context.obtainStyledAttributes，从主题中读取值。先获取当前上下文的主题，然后调用主题类的obtainStyledAttributes.

530    public final TypedArray obtainStyledAttributes(531            AttributeSet set, @StyleableRes int[] attrs) {532        return getTheme().obtainStyledAttributes(set, attrs, 0, 0);533    }

我们移步/frameworks/base/core/java/android/content/res/Resources.java，看看Theme中的obtainStyledAttributes的实现，我们删节一下，一共也没几句逻辑：

1593        public TypedArray obtainStyledAttributes(AttributeSet set,1594                @StyleableRes int[] attrs, @AttrRes int defStyleAttr, @StyleRes int defStyleRes) {1595            final int len = attrs.length;1596            final TypedArray array = TypedArray.obtain(Resources.this, len);1597...1602            final XmlBlock.Parser parser = (XmlBlock.Parser)set;1603            AssetManager.applyStyle(mTheme, defStyleAttr, defStyleRes,1604                    parser != null ? parser.mParseState : 0, attrs, array.mData, array.mIndices);16051606            array.mTheme = this;1607            array.mXml = parser;...1638            return array;1639        }

然后我们转战TypedArray.obtain：

43    static TypedArray obtain(Resources res, int len) {44        final TypedArray attrs = res.mTypedArrayPool.acquire();45        if (attrs != null) {46            attrs.mLength = len;47            attrs.mRecycled = false;4849            final int fullLen = len * AssetManager.STYLE_NUM_ENTRIES;50            if (attrs.mData.length >= fullLen) {51                return attrs;52            }5354            attrs.mData = new int[fullLen];55            attrs.mIndices = new int[1 + len];56            return attrs;57        }5859        return new TypedArray(res,60                new int[len*AssetManager.STYLE_NUM_ENTRIES],61                new int[1+len], len);62    }

得到了TypedArray结果之后，再通过setBaseAttributes将值设置好。上面已经反复强调了，在ViewGroup.LayoutParams一共就只有宽和高两个参数，不管怎么复杂地折腾，最终落实的一定是这两个值。

6881        /** 6882 * Extracts the layout parameters from the supplied attributes. 6883 * 6884 * @param a the style attributes to extract the parameters from 6885 * @param widthAttr the identifier of the width attribute 6886 * @param heightAttr the identifier of the height attribute 6887 */6888        protected void setBaseAttributes(TypedArray a, int widthAttr, int heightAttr) {6889            width = a.getLayoutDimension(widthAttr, "layout_width");6890            height = a.getLayoutDimension(heightAttr, "layout_height");6891        }

MarginLayoutParams

ViewGroup.LayoutParams只有宽和高两个参数，简单是极简了。下面我们给它周围加个白边。一共6个变量，上下左右4个边距，加上起始和结束2个边距。

6969    public static class MarginLayoutParams extends ViewGroup.LayoutParams {6970        /** 6971 * The left margin in pixels of the child. Margin values should be positive. 6972 * Call {@link ViewGroup#setLayoutParams(LayoutParams)} after reassigning a new value 6973 * to this field. 6974 */6975        @ViewDebug.ExportedProperty(category = "layout")6976        public int leftMargin;69776978        /** 6979 * The top margin in pixels of the child. Margin values should be positive. 6980 * Call {@link ViewGroup#setLayoutParams(LayoutParams)} after reassigning a new value 6981 * to this field. 6982 */6983        @ViewDebug.ExportedProperty(category = "layout")6984        public int topMargin;69856986        /** 6987 * The right margin in pixels of the child. Margin values should be positive. 6988 * Call {@link ViewGroup#setLayoutParams(LayoutParams)} after reassigning a new value 6989 * to this field. 6990 */6991        @ViewDebug.ExportedProperty(category = "layout")6992        public int rightMargin;69936994        /** 6995 * The bottom margin in pixels of the child. Margin values should be positive. 6996 * Call {@link ViewGroup#setLayoutParams(LayoutParams)} after reassigning a new value 6997 * to this field. 6998 */6999        @ViewDebug.ExportedProperty(category = "layout")7000        public int bottomMargin;70017002        /** 7003 * The start margin in pixels of the child. Margin values should be positive. 7004 * Call {@link ViewGroup#setLayoutParams(LayoutParams)} after reassigning a new value 7005 * to this field. 7006 */7007        @ViewDebug.ExportedProperty(category = "layout")7008        private int startMargin = DEFAULT_MARGIN_RELATIVE;70097010        /** 7011 * The end margin in pixels of the child. Margin values should be positive. 7012 * Call {@link ViewGroup#setLayoutParams(LayoutParams)} after reassigning a new value 7013 * to this field. 7014 */7015        @ViewDebug.ExportedProperty(category = "layout")7016        private int endMargin = DEFAULT_MARGIN_RELATIVE;

ViewGroup的构造

前三个都是陪太子读书的，一共是4个参数，前三个是给1个参数，2个参数，3个参数时其它给空参数时的调用。

560    public ViewGroup(Context context) {561        this(context, null);562    }563564    public ViewGroup(Context context, AttributeSet attrs) {565        this(context, attrs, 0);566    }567568    public ViewGroup(Context context, AttributeSet attrs, int defStyleAttr) {569        this(context, attrs, defStyleAttr, 0);570    }

其余就下面这一个，它一共有3步，我们分别分析。

572    public ViewGroup(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {573        super(context, attrs, defStyleAttr, defStyleRes);574        initViewGroup();575        initFromAttributes(context, attrs, defStyleAttr, defStyleRes);576    }

initViewGroup

这个好，基本上都是设一些属性

582    private void initViewGroup() {583        // ViewGroup doesn't draw by default584        if (!debugDraw()) {585            setFlags(WILL_NOT_DRAW, DRAW_MASK);586        }587        mGroupFlags |= FLAG_CLIP_CHILDREN;588        mGroupFlags |= FLAG_CLIP_TO_PADDING;589        mGroupFlags |= FLAG_ANIMATION_DONE;590        mGroupFlags |= FLAG_ANIMATION_CACHE;591        mGroupFlags |= FLAG_ALWAYS_DRAWN_WITH_CACHE;592593        if (mContext.getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.HONEYCOMB) {594            mGroupFlags |= FLAG_SPLIT_MOTION_EVENTS;595        }596597        setDescendantFocusability(FOCUS_BEFORE_DESCENDANTS);598599        mChildren = new View[ARRAY_INITIAL_CAPACITY];600        mChildrenCount = 0;601602        mPersistentDrawingCache = PERSISTENT_SCROLLING_CACHE;603    }

initFromAttributes

605    private void initFromAttributes(606            Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {

又到了我们熟悉的context.obtainStyledAttributes，下面就是分门别类放东西，就不多说了。

607        final TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.ViewGroup, defStyleAttr,608                defStyleRes);609610        final int N = a.getIndexCount();611        for (int i = 0; i < N; i++) {612            int attr = a.getIndex(i);613            switch (attr) {614                case R.styleable.ViewGroup_clipChildren:615                    setClipChildren(a.getBoolean(attr, true));616                    break;617                case R.styleable.ViewGroup_clipToPadding:618                    setClipToPadding(a.getBoolean(attr, true));619                    break;620                case R.styleable.ViewGroup_animationCache:621                    setAnimationCacheEnabled(a.getBoolean(attr, true));622                    break;623                case R.styleable.ViewGroup_persistentDrawingCache:624                    setPersistentDrawingCache(a.getInt(attr, PERSISTENT_SCROLLING_CACHE));625                    break;626                case R.styleable.ViewGroup_addStatesFromChildren:627                    setAddStatesFromChildren(a.getBoolean(attr, false));628                    break;629                case R.styleable.ViewGroup_alwaysDrawnWithCache:630                    setAlwaysDrawnWithCacheEnabled(a.getBoolean(attr, true));631                    break;632                case R.styleable.ViewGroup_layoutAnimation:633                    int id = a.getResourceId(attr, -1);634                    if (id > 0) {635                        setLayoutAnimation(AnimationUtils.loadLayoutAnimation(mContext, id));636                    }637                    break;638                case R.styleable.ViewGroup_descendantFocusability:639                    setDescendantFocusability(DESCENDANT_FOCUSABILITY_FLAGS[a.getInt(attr, 0)]);640                    break;641                case R.styleable.ViewGroup_splitMotionEvents:642                    setMotionEventSplittingEnabled(a.getBoolean(attr, false));643                    break;644                case R.styleable.ViewGroup_animateLayoutChanges:645                    boolean animateLayoutChanges = a.getBoolean(attr, false);646                    if (animateLayoutChanges) {647                        setLayoutTransition(new LayoutTransition());648                    }649                    break;650                case R.styleable.ViewGroup_layoutMode:651                    setLayoutMode(a.getInt(attr, LAYOUT_MODE_UNDEFINED));652                    break;653                case R.styleable.ViewGroup_transitionGroup:654                    setTransitionGroup(a.getBoolean(attr, false));655                    break;656                case R.styleable.ViewGroup_touchscreenBlocksFocus:657                    setTouchscreenBlocksFocus(a.getBoolean(attr, false));658                    break;659            }660        }661662        a.recycle();663    }

ViewGroup的父类 - View类

@UiThreadpublic class View implements Drawable.Callback, KeyEvent.Callback, AccessibilityEventSource {

这个类又是一个要求UiThread的类.

View类的构造方法，就是被ViewGroup类用super调用的那个，我们省略一些细节，看看它的结构：

3897    public View(Context context, @Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {3898        this(context);38993900        final TypedArray a = context.obtainStyledAttributes(3901                attrs, com.android.internal.R.styleable.View, defStyleAttr, defStyleRes);3902...39483949        final int N = a.getIndexCount();3950        for (int i = 0; i < N; i++) {3951            int attr = a.getIndex(i);3952            switch (attr) {3953                case com.android.internal.R.styleable.View_background:3954                    background = a.getDrawable(attr);3955                    break;...

我们把细节省略掉之后，跟ViewGroup刚才我们看到的构造函数已经非常像了。还是获取一个TypedArray对象，然后分门别类处理这些属性。

Android(安卓)Layout inflate分析(2) - ViewGroup