Android(安卓)View 绘制过程

Android的View绘制是从根节点（Activity是DecorView）开始，他是一个自上而下的过程。View的绘制经历三个过程：Measure、Layout、Draw。基本流程如下图：

performTraversals函数，具体的可以参考一下源代码：

1 private void performTraversals() {2     final View host = mView;3     ...4     host.measure(childWidthMeasureSpec, childHeightMeasureSpec);5     ...6     host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());7     ...8     draw(fullRedrawNeeded);9 }

1、Measure过程

Measure过程是计算视图大小，View中视图measure过程相关的方法主要有三个：

1 public final void measure(int widthMeasureSpec, int heightMeasureSpec)2 protected final void setMeasuredDimension(int measuredWidth, int measuredHeight)3 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)

measure调用onMeasure，onMeasure调用setMeasureDimension，measure，setMeasureDimension是final类型，view的子类不需要重写，onMeasure在view的子类中重写。

measure函数：

 1     public final void measure(int widthMeasureSpec, int heightMeasureSpec) { 2         if ((mPrivateFlags & FORCE_LAYOUT) == FORCE_LAYOUT || 3                 widthMeasureSpec != mOldWidthMeasureSpec || 4                 heightMeasureSpec != mOldHeightMeasureSpec) { 5  6             // first clears the measured dimension flag 7             mPrivateFlags &= ~MEASURED_DIMENSION_SET; 8  9             if (ViewDebug.TRACE_HIERARCHY) {10                 ViewDebug.trace(this, ViewDebug.HierarchyTraceType.ON_MEASURE);11             }12 13             // measure ourselves, this should set the measured dimension flag back14             onMeasure(widthMeasureSpec, heightMeasureSpec);15 16             // flag not set, setMeasuredDimension() was not invoked, we raise17             // an exception to warn the developer18             if ((mPrivateFlags & MEASURED_DIMENSION_SET) != MEASURED_DIMENSION_SET) {19                 throw new IllegalStateException("onMeasure() did not set the"20                         + " measured dimension by calling"21                         + " setMeasuredDimension()");22             }23 24             mPrivateFlags |= LAYOUT_REQUIRED;25         }26 27         mOldWidthMeasureSpec = widthMeasureSpec;28         mOldHeightMeasureSpec = heightMeasureSpec;29     }

onMeasure函数：

1     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {2         setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),3                 getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));4     }

重写onMeasure时，要调用setMeasuredDimension或者super.onMeasure来设置自身的mMeasuredWidth和mMeasuredHeight，否则，就会抛出异常.

setMeasuredDimension函数，用来设置view的大小：

1     protected final void setMeasuredDimension(int measuredWidth, int measuredHeight) {2         mMeasuredWidth = measuredWidth;3         mMeasuredHeight = measuredHeight;4 5         mPrivateFlags |= MEASURED_DIMENSION_SET;6     }

再看一下onMeasure的getDefaultSize函数：

 1     public static int getDefaultSize(int size, int measureSpec) { 2         int result = size; 3         int specMode = MeasureSpec.getMode(measureSpec); 4         int specSize = MeasureSpec.getSize(measureSpec); 5  6         switch (specMode) { 7         case MeasureSpec.UNSPECIFIED: 8             result = size; 9             break;10         case MeasureSpec.AT_MOST:11         case MeasureSpec.EXACTLY:12             result = specSize;13             break;14         }15         return result;16     }

这里用引入了MeasureSpec类：

 1     public static class MeasureSpec { 2  3         private static final int MODE_SHIFT = 30; 4         private static final int MODE_MASK  = 0x3 << MODE_SHIFT; 5         public static final int UNSPECIFIED = 0 << MODE_SHIFT; 6         public static final int EXACTLY     = 1 << MODE_SHIFT; 7         public static final int AT_MOST     = 2 << MODE_SHIFT; 8  9         public static int makeMeasureSpec(int size, int mode) {10             return size + mode;11         }12 13         public static int getMode(int measureSpec) {14             return (measureSpec & MODE_MASK);15         }16 17         public static int getSize(int measureSpec) {18             return (measureSpec & ~MODE_MASK);19         }20     }

MODE_MASK为30为长度的二进制数，前两位标示Mode，后面的标示Size。MeasureSpec有三种模式分别是UNSPECIFIED, EXACTLY和AT_MOST。

EXACTLY表示父视图希望子视图的大小应该是由specSize的值来决定的，系统默认会按照这个规则来设置子视图的大小，开发人员当然也可以按照自己的意愿设置成任意的大小。

AT_MOST表示子视图最多只能是specSize中指定的大小，开发人员应该尽可能小得去设置这个视图，并且保证不会超过specSize。系统默认会按照这个规则来设置子视图的大小，开发人员当然也可以按照自己的意愿设置成任意的大小。

UNSPECIFIED表示开发人员可以将视图按照自己的意愿设置成任意的大小，没有任何限制。这种情况比较少见，不太会用到。

widthMeasureSpec和heightMeasureSpec决定了Mode和Size的值，widthMeasureSpec和heightMeasureSpec来自父视图，这两个值都是由父视图经过计算后传递给子视图的，说明父视图会在一定程度上决定子视图的大小。但是最外层的根视图，它的widthMeasureSpec和heightMeasureSpec又是从哪里得到的呢？这就需要去分析ViewRoot中的源码了，观察performTraversals()方法可以发现如下代码：

1 childWidthMeasureSpec = getRootMeasureSpec(desiredWindowWidth, lp.width);2 childHeightMeasureSpec = getRootMeasureSpec(desiredWindowHeight, lp.height);

可以看到，这里调用了getRootMeasureSpec()方法去获取widthMeasureSpec和heightMeasureSpec的值，注意方法中传入的参数，其中lp.width和lp.height在创建ViewGroup实例的时候就被赋值了，它们都等于MATCH_PARENT。然后看下getRootMeasureSpec()方法中的代码，如下所示：

 1 private int getRootMeasureSpec(int windowSize, int rootDimension) { 2     int measureSpec; 3     switch (rootDimension) { 4     case ViewGroup.LayoutParams.MATCH_PARENT: 5         measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.EXACTLY); 6         break; 7     case ViewGroup.LayoutParams.WRAP_CONTENT: 8         measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.AT_MOST); 9         break;10     default:11         measureSpec = MeasureSpec.makeMeasureSpec(rootDimension, MeasureSpec.EXACTLY);12         break;13     }14     return measureSpec;15 }

可以看到，这里使用了MeasureSpec.makeMeasureSpec()方法来组装一个MeasureSpec，当rootDimension参数等于MATCH_PARENT的时候，MeasureSpec的specMode就等于EXACTLY，当rootDimension等于WRAP_CONTENT的时候，MeasureSpec的specMode就等于AT_MOST。并且MATCH_PARENT和WRAP_CONTENT时的specSize都是等于windowSize的，也就意味着根视图总是会充满全屏的。

Measure是一个复杂的过程，因为一个布局中一般都会包含多个子视图，每个视图都需要经历一次measure过程。ViewGroup中定义了一个measureChildren()方法来去测量子视图的大小，如下所示：

 1  protected void measureChildren(int widthMeasureSpec, int heightMeasureSpec) { 2         final int size = mChildrenCount; 3         final View[] children = mChildren; 4         for (int i = 0; i < size; ++i) { 5             final View child = children[i]; 6             if ((child.mViewFlags & VISIBILITY_MASK) != GONE) { 7                 measureChild(child, widthMeasureSpec, heightMeasureSpec); 8             } 9         }10     }

这里会去遍历当前布局下的所有子视图，然后逐个调用measureChild()方法来测量相应子视图的大小：

 1  protected void measureChild(View child, int parentWidthMeasureSpec, 2             int parentHeightMeasureSpec) { 3         final LayoutParams lp = child.getLayoutParams(); 4  5         final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec, 6                 mPaddingLeft + mPaddingRight, lp.width); 7         final int childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec, 8                 mPaddingTop + mPaddingBottom, lp.height); 9 10         child.measure(childWidthMeasureSpec, childHeightMeasureSpec);11     }

从这里我们可以看到视图的大小是由父视图和子视图共同决定的。子布局里面的android:layout_width和android:layout_height只是期望值，父View大小最终是由DecorView决定。父视图提供尺寸大小的一个能力，子视图最终尺寸与父视图能力、子视图期望的关系如下：

父视图能力尺寸	子视图期望尺寸	子视图最终允许尺寸
EXACTLY + Size1	EXACTLY + Size2	EXACTLY + Size2
EXACTLY + Size1	fill_parent/match_parent	EXACTLY+Size1
EXACTLY + Size1	wrap_content	AT_MOST+Size1
AT_MOST+Size1	EXACTLY + Size2	EXACTLY+Size2
AT_MOST+Size1	fill_parent/match_parent	AT_MOST+Size1
AT_MOST+Size1	wrap_content	AT_MOST+Size1
UNSPECIFIED+Size1	EXACTLY + Size2	EXACTLY + Size2
UNSPECIFIED+Size1	fill_parent/match_parent	UNSPECIFIED+0
UNSPECIFIED+Size1	wrap_content	UNSPECIFIED+0

关于视图的measure过程可以阅读以下LinearLayout源码，这样可以更清楚的了解过程。

2、Layout过程

measure过程确定视图的大小，而layout过程确定视图的位置。loyout是从view的layout方法开始的：

 1  public void layout(int l, int t, int r, int b) { 2         int oldL = mLeft; 3         int oldT = mTop; 4         int oldB = mBottom; 5         int oldR = mRight; 6         boolean changed = setFrame(l, t, r, b); 7         if (changed || (mPrivateFlags & PFLAG_LAYOUT_REQUIRED) == PFLAG_LAYOUT_REQUIRED) { 8             onLayout(changed, l, t, r, b); 9             mPrivateFlags &= ~PFLAG_LAYOUT_REQUIRED;10 11             ListenerInfo li = mListenerInfo;12             if (li != null && li.mOnLayoutChangeListeners != null) {13                 ArrayList listenersCopy =14                         (ArrayList)li.mOnLayoutChangeListeners.clone();15                 int numListeners = listenersCopy.size();16                 for (int i = 0; i < numListeners; ++i) {17                     listenersCopy.get(i).onLayoutChange(this, l, t, r, b, oldL, oldT, oldR, oldB);18                 }19             }20         }21         mPrivateFlags &= ~PFLAG_FORCE_LAYOUT;22     }

函数中参数l、t、r、b是指view的左、上、右、底的位置，这几个参数是父视图传入的，而根视图中参数是由performTraversals()方法传入的。

1   host.layout(0, 0, host.mMeasuredWidth, host.mMeasuredHeight);

layout中调用了onLayout方法，在view中onLayout方法是一个空函数，他需要其子类实现。

1 protected void onLayout(boolean changed, int left, int top, int right, int bottom) {2 }

我们关注一下LinearLayout：

1   @Override2     protected void onLayout(boolean changed, int l, int t, int r, int b) {3         if (mOrientation == VERTICAL) {4             layoutVertical();5         } else {6             layoutHorizontal();7         }8     }

 1   void layoutVertical() { 2         final int paddingLeft = mPaddingLeft; 3  4         int childTop; 5         int childLeft; 6          7         // Where right end of child should go 8         final int width = mRight - mLeft; 9         int childRight = width - mPaddingRight;10         11         // Space available for child12         int childSpace = width - paddingLeft - mPaddingRight;13         14         final int count = getVirtualChildCount();15 16         final int majorGravity = mGravity & Gravity.VERTICAL_GRAVITY_MASK;17         final int minorGravity = mGravity & Gravity.RELATIVE_HORIZONTAL_GRAVITY_MASK;18 19         switch (majorGravity) {20            case Gravity.BOTTOM:21                // mTotalLength contains the padding already22                childTop = mPaddingTop + mBottom - mTop - mTotalLength;23                break;24 25                // mTotalLength contains the padding already26            case Gravity.CENTER_VERTICAL:27                childTop = mPaddingTop + (mBottom - mTop - mTotalLength) / 2;28                break;29 30            case Gravity.TOP:31            default:32                childTop = mPaddingTop;33                break;34         }35 36         for (int i = 0; i < count; i++) {37             final View child = getVirtualChildAt(i);38             if (child == null) {39                 childTop += measureNullChild(i);40             } else if (child.getVisibility() != GONE) {41                 final int childWidth = child.getMeasuredWidth();42                 final int childHeight = child.getMeasuredHeight();43                 44                 final LinearLayout.LayoutParams lp =45                         (LinearLayout.LayoutParams) child.getLayoutParams();46                 47                 int gravity = lp.gravity;48                 if (gravity < 0) {49                     gravity = minorGravity;50                 }51                 final int layoutDirection = getLayoutDirection();52                 final int absoluteGravity = Gravity.getAbsoluteGravity(gravity, layoutDirection);53                 switch (absoluteGravity & Gravity.HORIZONTAL_GRAVITY_MASK) {54                     case Gravity.CENTER_HORIZONTAL:55                         childLeft = paddingLeft + ((childSpace - childWidth) / 2)56                                 + lp.leftMargin - lp.rightMargin;57                         break;58 59                     case Gravity.RIGHT:60                         childLeft = childRight - childWidth - lp.rightMargin;61                         break;62 63                     case Gravity.LEFT:64                     default:65                         childLeft = paddingLeft + lp.leftMargin;66                         break;67                 }68 69                 if (hasDividerBeforeChildAt(i)) {70                     childTop += mDividerHeight;71                 }72 73                 childTop += lp.topMargin;74                 setChildFrame(child, childLeft, childTop + getLocationOffset(child),75                         childWidth, childHeight);76                 childTop += childHeight + lp.bottomMargin + getNextLocationOffset(child);77 78                 i += getChildrenSkipCount(child, i);79             }80         }81     }

layout设置了view的位置，还设置了子视图位置，layoutHorizontal()方法中调用了setChildFrame方法：

1     private void setChildFrame(View child, int left, int top, int width, int height) {        2         child.layout(left, top, left + width, top + height);3     }4

从上面看出，layout也是一个自上而下的过程，先设置父视图位置，在循环子视图，父视图位置一定程度上决定了子视图位置。

3、Draw过程

draw过程调用顺序在measure()和layout()之后，同样的，performTraversals()发起的draw过程最终会调用到mView的draw()函数，这里的mView对于Activity来说就是PhoneWindow.DecorView。看一下view类的draw方法：

  1  public void draw(Canvas canvas) {  2         final int privateFlags = mPrivateFlags;  3         final boolean dirtyOpaque = (privateFlags & PFLAG_DIRTY_MASK) == PFLAG_DIRTY_OPAQUE &&  4                 (mAttachInfo == null || !mAttachInfo.mIgnoreDirtyState);  5         mPrivateFlags = (privateFlags & ~PFLAG_DIRTY_MASK) | PFLAG_DRAWN;  6   7         /*  8          * Draw traversal performs several drawing steps which must be executed  9          * in the appropriate order: 10          * 11          *      1. Draw the background 12          *      2. If necessary, save the canvas‘ layers to prepare for fading 13          *      3. Draw view‘s content 14          *      4. Draw children 15          *      5. If necessary, draw the fading edges and restore layers 16          *      6. Draw decorations (scrollbars for instance) 17          */ 18  19         // Step 1, draw the background, if needed 20         int saveCount; 21  22         if (!dirtyOpaque) { 23             final Drawable background = mBackground; 24             if (background != null) { 25                 final int scrollX = mScrollX; 26                 final int scrollY = mScrollY; 27  28                 if (mBackgroundSizeChanged) { 29                     background.setBounds(0, 0,  mRight - mLeft, mBottom - mTop); 30                     mBackgroundSizeChanged = false; 31                 } 32  33                 if ((scrollX | scrollY) == 0) { 34                     background.draw(canvas); 35                 } else { 36                     canvas.translate(scrollX, scrollY); 37                     background.draw(canvas); 38                     canvas.translate(-scrollX, -scrollY); 39                 } 40             } 41         } 42  43         // skip step 2 & 5 if possible (common case) 44         final int viewFlags = mViewFlags; 45         boolean horizontalEdges = (viewFlags & FADING_EDGE_HORIZONTAL) != 0; 46         boolean verticalEdges = (viewFlags & FADING_EDGE_VERTICAL) != 0; 47         if (!verticalEdges && !horizontalEdges) { 48             // Step 3, draw the content 49             if (!dirtyOpaque) onDraw(canvas); 50  51             // Step 4, draw the children 52             dispatchDraw(canvas); 53  54             // Step 6, draw decorations (scrollbars) 55             onDrawScrollBars(canvas); 56  57             // we‘re done... 58             return; 59         } 60  61         /* 62          * Here we do the full fledged routine... 63          * (this is an uncommon case where speed matters less, 64          * this is why we repeat some of the tests that have been 65          * done above) 66          */ 67  68         boolean drawTop = false; 69         boolean drawBottom = false; 70         boolean drawLeft = false; 71         boolean drawRight = false; 72  73         float topFadeStrength = 0.0f; 74         float bottomFadeStrength = 0.0f; 75         float leftFadeStrength = 0.0f; 76         float rightFadeStrength = 0.0f; 77  78         // Step 2, save the canvas‘ layers 79         int paddingLeft = mPaddingLeft; 80  81         final boolean offsetRequired = isPaddingOffsetRequired(); 82         if (offsetRequired) { 83             paddingLeft += getLeftPaddingOffset(); 84         } 85  86         int left = mScrollX + paddingLeft; 87         int right = left + mRight - mLeft - mPaddingRight - paddingLeft; 88         int top = mScrollY + getFadeTop(offsetRequired); 89         int bottom = top + getFadeHeight(offsetRequired); 90  91         if (offsetRequired) { 92             right += getRightPaddingOffset(); 93             bottom += getBottomPaddingOffset(); 94         } 95  96         final ScrollabilityCache scrollabilityCache = mScrollCache; 97         final float fadeHeight = scrollabilityCache.fadingEdgeLength; 98         int length = (int) fadeHeight; 99 100         // clip the fade length if top and bottom fades overlap101         // overlapping fades produce odd-looking artifacts102         if (verticalEdges && (top + length > bottom - length)) {103             length = (bottom - top) / 2;104         }105 106         // also clip horizontal fades if necessary107         if (horizontalEdges && (left + length > right - length)) {108             length = (right - left) / 2;109         }110 111         if (verticalEdges) {112             topFadeStrength = Math.max(0.0f, Math.min(1.0f, getTopFadingEdgeStrength()));113             drawTop = topFadeStrength * fadeHeight > 1.0f;114             bottomFadeStrength = Math.max(0.0f, Math.min(1.0f, getBottomFadingEdgeStrength()));115             drawBottom = bottomFadeStrength * fadeHeight > 1.0f;116         }117 118         if (horizontalEdges) {119             leftFadeStrength = Math.max(0.0f, Math.min(1.0f, getLeftFadingEdgeStrength()));120             drawLeft = leftFadeStrength * fadeHeight > 1.0f;121             rightFadeStrength = Math.max(0.0f, Math.min(1.0f, getRightFadingEdgeStrength()));122             drawRight = rightFadeStrength * fadeHeight > 1.0f;123         }124 125         saveCount = canvas.getSaveCount();126 127         int solidColor = getSolidColor();128         if (solidColor == 0) {129             final int flags = Canvas.HAS_ALPHA_LAYER_SAVE_FLAG;130 131             if (drawTop) {132                 canvas.saveLayer(left, top, right, top + length, null, flags);133             }134 135             if (drawBottom) {136                 canvas.saveLayer(left, bottom - length, right, bottom, null, flags);137             }138 139             if (drawLeft) {140                 canvas.saveLayer(left, top, left + length, bottom, null, flags);141             }142 143             if (drawRight) {144                 canvas.saveLayer(right - length, top, right, bottom, null, flags);145             }146         } else {147             scrollabilityCache.setFadeColor(solidColor);148         }149 150         // Step 3, draw the content151         if (!dirtyOpaque) onDraw(canvas);152 153         // Step 4, draw the children154         dispatchDraw(canvas);155 156         // Step 5, draw the fade effect and restore layers157         final Paint p = scrollabilityCache.paint;158         final Matrix matrix = scrollabilityCache.matrix;159         final Shader fade = scrollabilityCache.shader;160 161         if (drawTop) {162             matrix.setScale(1, fadeHeight * topFadeStrength);163             matrix.postTranslate(left, top);164             fade.setLocalMatrix(matrix);165             canvas.drawRect(left, top, right, top + length, p);166         }167 168         if (drawBottom) {169             matrix.setScale(1, fadeHeight * bottomFadeStrength);170             matrix.postRotate(180);171             matrix.postTranslate(left, bottom);172             fade.setLocalMatrix(matrix);173             canvas.drawRect(left, bottom - length, right, bottom, p);174         }175 176         if (drawLeft) {177             matrix.setScale(1, fadeHeight * leftFadeStrength);178             matrix.postRotate(-90);179             matrix.postTranslate(left, top);180             fade.setLocalMatrix(matrix);181             canvas.drawRect(left, top, left + length, bottom, p);182         }183 184         if (drawRight) {185             matrix.setScale(1, fadeHeight * rightFadeStrength);186             matrix.postRotate(90);187             matrix.postTranslate(right, top);188             fade.setLocalMatrix(matrix);189             canvas.drawRect(right - length, top, right, bottom, p);190         }191 192         canvas.restoreToCount(saveCount);193 194         // Step 6, draw decorations (scrollbars)195         onDrawScrollBars(canvas);196     }

draw方法分成了6个步骤：

 1  /* 2          * Draw traversal performs several drawing steps which must be executed 3          * in the appropriate order: 4          * 5          *      1. Draw the background 6          *      2. If necessary, save the canvas‘ layers to prepare for fading 7          *      3. Draw view‘s content 8          *      4. Draw children 9          *      5. If necessary, draw the fading edges and restore layers10          *      6. Draw decorations (scrollbars for instance)11          */

第三部, Draw view‘s content步骤调用了onDraw方法，子类中实现onDraw方法。

第四步，Draw children步骤使用的dispatchDraw方法，这个方法在ViewGroup中有实现。

View或ViewGroup的子类不用再重载ViewGroup中该方法，因为它已经有了默认而且标准的view系统流程。dispatchDraw()内部for循环调用drawChild()分别绘制每一个子视图，而drawChild()内部又会调用draw（）函数完成子视图的内部绘制工作。

  1  /**  2      * {@inheritDoc}  3      */  4     @Override  5     protected void dispatchDraw(Canvas canvas) {  6         final int count = mChildrenCount;  7         final View[] children = mChildren;  8         int flags = mGroupFlags;  9  10         if ((flags & FLAG_RUN_ANIMATION) != 0 && canAnimate()) { 11             final boolean cache = (mGroupFlags & FLAG_ANIMATION_CACHE) == FLAG_ANIMATION_CACHE; 12  13             final boolean buildCache = !isHardwareAccelerated(); 14             for (int i = 0; i < count; i++) { 15                 final View child = children[i]; 16                 if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE) { 17                     final LayoutParams params = child.getLayoutParams(); 18                     attachLayoutAnimationParameters(child, params, i, count); 19                     bindLayoutAnimation(child); 20                     if (cache) { 21                         child.setDrawingCacheEnabled(true); 22                         if (buildCache) {                         23                             child.buildDrawingCache(true); 24                         } 25                     } 26                 } 27             } 28  29             final LayoutAnimationController controller = mLayoutAnimationController; 30             if (controller.willOverlap()) { 31                 mGroupFlags |= FLAG_OPTIMIZE_INVALIDATE; 32             } 33  34             controller.start(); 35  36             mGroupFlags &= ~FLAG_RUN_ANIMATION; 37             mGroupFlags &= ~FLAG_ANIMATION_DONE; 38  39             if (cache) { 40                 mGroupFlags |= FLAG_CHILDREN_DRAWN_WITH_CACHE; 41             } 42  43             if (mAnimationListener != null) { 44                 mAnimationListener.onAnimationStart(controller.getAnimation()); 45             } 46         } 47  48         int saveCount = 0; 49         final boolean clipToPadding = (flags & CLIP_TO_PADDING_MASK) == CLIP_TO_PADDING_MASK; 50         if (clipToPadding) { 51             saveCount = canvas.save(); 52             canvas.clipRect(mScrollX + mPaddingLeft, mScrollY + mPaddingTop, 53                     mScrollX + mRight - mLeft - mPaddingRight, 54                     mScrollY + mBottom - mTop - mPaddingBottom); 55  56         } 57  58         // We will draw our child‘s animation, let‘s reset the flag 59         mPrivateFlags &= ~PFLAG_DRAW_ANIMATION; 60         mGroupFlags &= ~FLAG_INVALIDATE_REQUIRED; 61  62         boolean more = false; 63         final long drawingTime = getDrawingTime(); 64  65         if ((flags & FLAG_USE_CHILD_DRAWING_ORDER) == 0) { 66             for (int i = 0; i < count; i++) { 67                 final View child = children[i]; 68                 if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE || child.getAnimation() != null) { 69                     more |= drawChild(canvas, child, drawingTime); 70                 } 71             } 72         } else { 73             for (int i = 0; i < count; i++) { 74                 final View child = children[getChildDrawingOrder(count, i)]; 75                 if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE || child.getAnimation() != null) { 76                     more |= drawChild(canvas, child, drawingTime); 77                 } 78             } 79         } 80  81         // Draw any disappearing views that have animations 82         if (mDisappearingChildren != null) { 83             final ArrayList disappearingChildren = mDisappearingChildren; 84             final int disappearingCount = disappearingChildren.size() - 1; 85             // Go backwards -- we may delete as animations finish 86             for (int i = disappearingCount; i >= 0; i--) { 87                 final View child = disappearingChildren.get(i); 88                 more |= drawChild(canvas, child, drawingTime); 89             } 90         } 91  92         if (debugDraw()) { 93             onDebugDraw(canvas); 94         } 95  96         if (clipToPadding) { 97             canvas.restoreToCount(saveCount); 98         } 99 100         // mGroupFlags might have been updated by drawChild()101         flags = mGroupFlags;102 103         if ((flags & FLAG_INVALIDATE_REQUIRED) == FLAG_INVALIDATE_REQUIRED) {104             invalidate(true);105         }106 107         if ((flags & FLAG_ANIMATION_DONE) == 0 && (flags & FLAG_NOTIFY_ANIMATION_LISTENER) == 0 &&108                 mLayoutAnimationController.isDone() && !more) {109             // We want to erase the drawing cache and notify the listener after the110             // next frame is drawn because one extra invalidate() is caused by111             // drawChild() after the animation is over112             mGroupFlags |= FLAG_NOTIFY_ANIMATION_LISTENER;113             final Runnable end = new Runnable() {114                public void run() {115                    notifyAnimationListener();116                }117             };118             post(end);119         }120     }

上面基本介绍完了View的绘制流程。更多的细节需要在日常学习中总结。

转自：http://blog.csdn.net/xyz_lmn/article/details/20385049

1、Measure过程

2、Layout过程

3、Draw过程

更多相关文章

随机推荐