Android View繪製過程
Android的View繪製是從根節點（Activity是DecorView）開始，他是一個自上而下的過程。View的繪製經歷三個過程：Measure、Layout、Draw。基本流程以下圖：html
performTraversals函數，具體的能夠參考一下源代碼：java
private void performTraversals() {
final View host = mView;
...
host.measure(childWidthMeasureSpec, childHeightMeasureSpec);
...
host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());
...
draw(fullRedrawNeeded);
}
一、Measure過程
Measure過程是計算視圖大小，View中視圖measure過程相關的方法主要有三個：android
public final void measure(int widthMeasureSpec, int heightMeasureSpec) protected final void setMeasuredDimension(int measuredWidth, int measuredHeight) protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
measure調用onMeasure，onMeasure調用setMeasureDimension，measure，setMeasureDimension是final類型，view的子類不須要重寫，onMeasure在view的子類中重寫。canvas
measure函數：app
public final void measure(int widthMeasureSpec, int heightMeasureSpec) {
if ((mPrivateFlags & FORCE_LAYOUT) == FORCE_LAYOUT ||
widthMeasureSpec != mOldWidthMeasureSpec ||
heightMeasureSpec != mOldHeightMeasureSpec) {
// first clears the measured dimension flag
mPrivateFlags &= ~MEASURED_DIMENSION_SET;
if (ViewDebug.TRACE_HIERARCHY) {
ViewDebug.trace(this, ViewDebug.HierarchyTraceType.ON_MEASURE);
}
// measure ourselves, this should set the measured dimension flag back
onMeasure(widthMeasureSpec, heightMeasureSpec);
// flag not set, setMeasuredDimension() was not invoked, we raise
// an exception to warn the developer
if ((mPrivateFlags & MEASURED_DIMENSION_SET) != MEASURED_DIMENSION_SET) {
throw new IllegalStateException("onMeasure() did not set the"
+ " measured dimension by calling"
+ " setMeasuredDimension()");
}
mPrivateFlags |= LAYOUT_REQUIRED;
}
mOldWidthMeasureSpec = widthMeasureSpec;
mOldHeightMeasureSpec = heightMeasureSpec;
}
onMeasure函數：
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));
}
重寫onMeasure時，要調用setMeasuredDimension或者super.onMeasure來設置自身的mMeasuredWidth和mMeasuredHeight，不然，就會拋出異常.less
setMeasuredDimension函數，用來設置view的大小：
ide
protected final void setMeasuredDimension(int measuredWidth, int measuredHeight) {
mMeasuredWidth = measuredWidth;
mMeasuredHeight = measuredHeight;
mPrivateFlags |= MEASURED_DIMENSION_SET;
}
再看一下onMeasure的getDefaultSize函數：函數
public static int getDefaultSize(int size, int measureSpec) {
int result = size;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
switch (specMode) {
case MeasureSpec.UNSPECIFIED:
result = size;
break;
case MeasureSpec.AT_MOST:
case MeasureSpec.EXACTLY:
result = specSize;
break;
}
return result;
}
這裏用引入了 MeasureSpec類：
public static class MeasureSpec {
private static final int MODE_SHIFT = 30;
private static final int MODE_MASK = 0x3 << MODE_SHIFT;
public static final int UNSPECIFIED = 0 << MODE_SHIFT;
public static final int EXACTLY = 1 << MODE_SHIFT;
public static final int AT_MOST = 2 << MODE_SHIFT;
public static int makeMeasureSpec(int size, int mode) {
return size + mode;
}
public static int getMode(int measureSpec) {
return (measureSpec & MODE_MASK);
}
public static int getSize(int measureSpec) {
return (measureSpec & ~MODE_MASK);
}
}
MODE_MASK爲30爲長度的二進制數，前兩位標示Mode，後面的標示Size。MeasureSpec有三種模式分別是UNSPECIFIED, EXACTLY和AT_MOST。佈局
EXACTLY表示父視圖但願子視圖的大小應該是由specSize的值來決定的，系統默認會按照這個規則來設置子視圖的大小，開發人員固然也能夠按照本身的意願設置成任意的大小。
post
AT_MOST表示子視圖最多隻能是specSize中指定的大小，開發人員應該儘量小得去設置這個視圖，而且保證不會超過specSize。系統默認會按照這個規則來設置子視圖的大小，開發人員固然也能夠按照本身的意願設置成任意的大小。
UNSPECIFIED表示開發人員能夠將視圖按照本身的意願設置成任意的大小，沒有任何限制。這種狀況比較少見，不太會用到。
widthMeasureSpec和heightMeasureSpec決定了Mode和Size的值，widthMeasureSpec和heightMeasureSpec來自父視圖，這兩個值都是由父視圖通過計算後傳遞給子視圖的，說明父視圖會在必定程度上決定子視圖的大小。可是最外層的根視圖，它的widthMeasureSpec和heightMeasureSpec又是從哪裏獲得的呢？這就須要去分析ViewRoot中的源碼了，觀察performTraversals()方法能夠發現以下代碼：
childWidthMeasureSpec = getRootMeasureSpec(desiredWindowWidth, lp.width); childHeightMeasureSpec = getRootMeasureSpec(desiredWindowHeight, lp.height);
能夠看到，這裏調用了getRootMeasureSpec()方法去獲取widthMeasureSpec和heightMeasureSpec的值，注意方法中傳入的參數，其中lp.width和lp.height在建立ViewGroup實例的時候就被賦值了，它們都等於MATCH_PARENT。而後看下getRootMeasureSpec()方法中的代碼，以下所示：
private int getRootMeasureSpec(int windowSize, int rootDimension) {
int measureSpec;
switch (rootDimension) {
case ViewGroup.LayoutParams.MATCH_PARENT:
measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.EXACTLY);
break;
case ViewGroup.LayoutParams.WRAP_CONTENT:
measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.AT_MOST);
break;
default:
measureSpec = MeasureSpec.makeMeasureSpec(rootDimension, MeasureSpec.EXACTLY);
break;
}
return measureSpec;
}
能夠看到，這裏使用了MeasureSpec.makeMeasureSpec()方法來組裝一個MeasureSpec，當rootDimension參數等於MATCH_PARENT的時候，MeasureSpec的specMode就等於EXACTLY，當rootDimension等於WRAP_CONTENT的時候，MeasureSpec的specMode就等於AT_MOST。而且MATCH_PARENT和WRAP_CONTENT時的specSize都是等於windowSize的，也就意味着根視圖老是會充滿全屏的。
Measure是一個複雜的過程，由於一個佈局中通常都會包含多個子視圖，每一個視圖都須要經歷一次measure過程。ViewGroup中定義了一個measureChildren()方法來去測量子視圖的大小，以下所示：
protected void measureChildren(int widthMeasureSpec, int heightMeasureSpec) {
final int size = mChildrenCount;
final View[] children = mChildren;
for (int i = 0; i < size; ++i) {
final View child = children[i];
if ((child.mViewFlags & VISIBILITY_MASK) != GONE) {
measureChild(child, widthMeasureSpec, heightMeasureSpec);
}
}
}
這裏會去遍歷當前佈局下的全部子視圖，而後逐個調用measureChild()方法來測量相應子視圖的大小：
protected void measureChild(View child, int parentWidthMeasureSpec,
int parentHeightMeasureSpec) {
final LayoutParams lp = child.getLayoutParams();
final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,
mPaddingLeft + mPaddingRight, lp.width);
final int childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec,
mPaddingTop + mPaddingBottom, lp.height);
child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
}
從這裏咱們能夠看到視圖的大小是由父視圖和子視圖共同決定的。子佈局裏面的android:layout_width和android:layout_height只是指望值，父View大小最終是由DecorView決定。父視圖提供尺寸大小的一個能力，子視圖最終尺寸與父視圖能力、子視圖指望的關係以下：
父視圖能力尺寸 |
子視圖指望尺寸 |
子視圖最終容許尺寸 |
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 |
關於視圖的measure過程能夠閱讀如下LinearLayout源碼，這樣能夠更清楚的瞭解過程。
二、Layout過程
measure過程肯定視圖的大小，而layout過程肯定視圖的位置。loyout是從view的layout方法開始的：
public void layout(int l, int t, int r, int b) {
int oldL = mLeft;
int oldT = mTop;
int oldB = mBottom;
int oldR = mRight;
boolean changed = setFrame(l, t, r, b);
if (changed || (mPrivateFlags & PFLAG_LAYOUT_REQUIRED) == PFLAG_LAYOUT_REQUIRED) {
onLayout(changed, l, t, r, b);
mPrivateFlags &= ~PFLAG_LAYOUT_REQUIRED;
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnLayoutChangeListeners != null) {
ArrayList<OnLayoutChangeListener> listenersCopy =
(ArrayList<OnLayoutChangeListener>)li.mOnLayoutChangeListeners.clone();
int numListeners = listenersCopy.size();
for (int i = 0; i < numListeners; ++i) {
listenersCopy.get(i).onLayoutChange(this, l, t, r, b, oldL, oldT, oldR, oldB);
}
}
}
mPrivateFlags &= ~PFLAG_FORCE_LAYOUT;
}
函數中參數l、t、r、b是指view的左、上、右、底的位置，這幾個參數是父視圖傳入的，而根視圖中參數是由 performTraversals()方法傳入的。
host.layout(0, 0, host.mMeasuredWidth, host.mMeasuredHeight);
layout中調用了onLayout方法，在view中onLayout方法是一個空函數，他須要其子類實現。
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
}
咱們關注一下LinearLayout：
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
if (mOrientation == VERTICAL) {
layoutVertical();
} else {
layoutHorizontal();
}
}
void layoutVertical() {
final int paddingLeft = mPaddingLeft;
int childTop;
int childLeft;
// Where right end of child should go
final int width = mRight - mLeft;
int childRight = width - mPaddingRight;
// Space available for child
int childSpace = width - paddingLeft - mPaddingRight;
final int count = getVirtualChildCount();
final int majorGravity = mGravity & Gravity.VERTICAL_GRAVITY_MASK;
final int minorGravity = mGravity & Gravity.RELATIVE_HORIZONTAL_GRAVITY_MASK;
switch (majorGravity) {
case Gravity.BOTTOM:
// mTotalLength contains the padding already
childTop = mPaddingTop + mBottom - mTop - mTotalLength;
break;
// mTotalLength contains the padding already
case Gravity.CENTER_VERTICAL:
childTop = mPaddingTop + (mBottom - mTop - mTotalLength) / 2;
break;
case Gravity.TOP:
default:
childTop = mPaddingTop;
break;
}
for (int i = 0; i < count; i++) {
final View child = getVirtualChildAt(i);
if (child == null) {
childTop += measureNullChild(i);
} else if (child.getVisibility() != GONE) {
final int childWidth = child.getMeasuredWidth();
final int childHeight = child.getMeasuredHeight();
final LinearLayout.LayoutParams lp =
(LinearLayout.LayoutParams) child.getLayoutParams();
int gravity = lp.gravity;
if (gravity < 0) {
gravity = minorGravity;
}
final int layoutDirection = getLayoutDirection();
final int absoluteGravity = Gravity.getAbsoluteGravity(gravity, layoutDirection);
switch (absoluteGravity & Gravity.HORIZONTAL_GRAVITY_MASK) {
case Gravity.CENTER_HORIZONTAL:
childLeft = paddingLeft + ((childSpace - childWidth) / 2)
+ lp.leftMargin - lp.rightMargin;
break;
case Gravity.RIGHT:
childLeft = childRight - childWidth - lp.rightMargin;
break;
case Gravity.LEFT:
default:
childLeft = paddingLeft + lp.leftMargin;
break;
}
if (hasDividerBeforeChildAt(i)) {
childTop += mDividerHeight;
}
childTop += lp.topMargin;
setChildFrame(child, childLeft, childTop + getLocationOffset(child),
childWidth, childHeight);
childTop += childHeight + lp.bottomMargin + getNextLocationOffset(child);
i += getChildrenSkipCount(child, i);
}
}
}
layout設置了view的位置，還設置了子視圖位置， layoutHorizontal()方法中調用了setChildFrame方法：
private void setChildFrame(View child, int left, int top, int width, int height) {
child.layout(left, top, left + width, top + height);
}
從上面看出，layout也是一個自上而下的過程，先設置父視圖位置，在循環子視圖，父視圖位置必定程度上決定了子視圖位置。
三、Draw過程
draw過程調用順序在measure()和layout()以後，一樣的，performTraversals()發起的draw過程最終會調用到mView的draw()函數，這裏的mView對於Activity來講就是PhoneWindow.DecorView。看一下view類的draw方法：
public void draw(Canvas canvas) {
final int privateFlags = mPrivateFlags;
final boolean dirtyOpaque = (privateFlags & PFLAG_DIRTY_MASK) == PFLAG_DIRTY_OPAQUE &&
(mAttachInfo == null || !mAttachInfo.mIgnoreDirtyState);
mPrivateFlags = (privateFlags & ~PFLAG_DIRTY_MASK) | PFLAG_DRAWN;
/*
* Draw traversal performs several drawing steps which must be executed
* in the appropriate order:
*
* 1. Draw the background
* 2. If necessary, save the canvas' layers to prepare for fading
* 3. Draw view's content
* 4. Draw children
* 5. If necessary, draw the fading edges and restore layers
* 6. Draw decorations (scrollbars for instance)
*/
// Step 1, draw the background, if needed
int saveCount;
if (!dirtyOpaque) {
final Drawable background = mBackground;
if (background != null) {
final int scrollX = mScrollX;
final int scrollY = mScrollY;
if (mBackgroundSizeChanged) {
background.setBounds(0, 0, mRight - mLeft, mBottom - mTop);
mBackgroundSizeChanged = false;
}
if ((scrollX | scrollY) == 0) {
background.draw(canvas);
} else {
canvas.translate(scrollX, scrollY);
background.draw(canvas);
canvas.translate(-scrollX, -scrollY);
}
}
}
// skip step 2 & 5 if possible (common case)
final int viewFlags = mViewFlags;
boolean horizontalEdges = (viewFlags & FADING_EDGE_HORIZONTAL) != 0;
boolean verticalEdges = (viewFlags & FADING_EDGE_VERTICAL) != 0;
if (!verticalEdges && !horizontalEdges) {
// Step 3, draw the content
if (!dirtyOpaque) onDraw(canvas);
// Step 4, draw the children
dispatchDraw(canvas);
// Step 6, draw decorations (scrollbars)
onDrawScrollBars(canvas);
// we're done...
return;
}
/*
* Here we do the full fledged routine...
* (this is an uncommon case where speed matters less,
* this is why we repeat some of the tests that have been
* done above)
*/
boolean drawTop = false;
boolean drawBottom = false;
boolean drawLeft = false;
boolean drawRight = false;
float topFadeStrength = 0.0f;
float bottomFadeStrength = 0.0f;
float leftFadeStrength = 0.0f;
float rightFadeStrength = 0.0f;
// Step 2, save the canvas' layers
int paddingLeft = mPaddingLeft;
final boolean offsetRequired = isPaddingOffsetRequired();
if (offsetRequired) {
paddingLeft += getLeftPaddingOffset();
}
int left = mScrollX + paddingLeft;
int right = left + mRight - mLeft - mPaddingRight - paddingLeft;
int top = mScrollY + getFadeTop(offsetRequired);
int bottom = top + getFadeHeight(offsetRequired);
if (offsetRequired) {
right += getRightPaddingOffset();
bottom += getBottomPaddingOffset();
}
final ScrollabilityCache scrollabilityCache = mScrollCache;
final float fadeHeight = scrollabilityCache.fadingEdgeLength;
int length = (int) fadeHeight;
// clip the fade length if top and bottom fades overlap
// overlapping fades produce odd-looking artifacts
if (verticalEdges && (top + length > bottom - length)) {
length = (bottom - top) / 2;
}
// also clip horizontal fades if necessary
if (horizontalEdges && (left + length > right - length)) {
length = (right - left) / 2;
}
if (verticalEdges) {
topFadeStrength = Math.max(0.0f, Math.min(1.0f, getTopFadingEdgeStrength()));
drawTop = topFadeStrength * fadeHeight > 1.0f;
bottomFadeStrength = Math.max(0.0f, Math.min(1.0f, getBottomFadingEdgeStrength()));
drawBottom = bottomFadeStrength * fadeHeight > 1.0f;
}
if (horizontalEdges) {
leftFadeStrength = Math.max(0.0f, Math.min(1.0f, getLeftFadingEdgeStrength()));
drawLeft = leftFadeStrength * fadeHeight > 1.0f;
rightFadeStrength = Math.max(0.0f, Math.min(1.0f, getRightFadingEdgeStrength()));
drawRight = rightFadeStrength * fadeHeight > 1.0f;
}
saveCount = canvas.getSaveCount();
int solidColor = getSolidColor();
if (solidColor == 0) {
final int flags = Canvas.HAS_ALPHA_LAYER_SAVE_FLAG;
if (drawTop) {
canvas.saveLayer(left, top, right, top + length, null, flags);
}
if (drawBottom) {
canvas.saveLayer(left, bottom - length, right, bottom, null, flags);
}
if (drawLeft) {
canvas.saveLayer(left, top, left + length, bottom, null, flags);
}
if (drawRight) {
canvas.saveLayer(right - length, top, right, bottom, null, flags);
}
} else {
scrollabilityCache.setFadeColor(solidColor);
}
// Step 3, draw the content
if (!dirtyOpaque) onDraw(canvas);
// Step 4, draw the children
dispatchDraw(canvas);
// Step 5, draw the fade effect and restore layers
final Paint p = scrollabilityCache.paint;
final Matrix matrix = scrollabilityCache.matrix;
final Shader fade = scrollabilityCache.shader;
if (drawTop) {
matrix.setScale(1, fadeHeight * topFadeStrength);
matrix.postTranslate(left, top);
fade.setLocalMatrix(matrix);
canvas.drawRect(left, top, right, top + length, p);
}
if (drawBottom) {
matrix.setScale(1, fadeHeight * bottomFadeStrength);
matrix.postRotate(180);
matrix.postTranslate(left, bottom);
fade.setLocalMatrix(matrix);
canvas.drawRect(left, bottom - length, right, bottom, p);
}
if (drawLeft) {
matrix.setScale(1, fadeHeight * leftFadeStrength);
matrix.postRotate(-90);
matrix.postTranslate(left, top);
fade.setLocalMatrix(matrix);
canvas.drawRect(left, top, left + length, bottom, p);
}
if (drawRight) {
matrix.setScale(1, fadeHeight * rightFadeStrength);
matrix.postRotate(90);
matrix.postTranslate(right, top);
fade.setLocalMatrix(matrix);
canvas.drawRect(right - length, top, right, bottom, p);
}
canvas.restoreToCount(saveCount);
// Step 6, draw decorations (scrollbars)
onDrawScrollBars(canvas);
}
draw方法分紅了6個步驟：
/*
* Draw traversal performs several drawing steps which must be executed
* in the appropriate order:
*
* 1. Draw the background
* 2. If necessary, save the canvas' layers to prepare for fading
* 3. Draw view's content
* 4. Draw children
* 5. If necessary, draw the fading edges and restore layers
* 6. Draw decorations (scrollbars for instance)
*/
第三部, Draw view's content步驟調用了onDraw方法，子類中實現onDraw方法。
第四步，Draw children步驟使用的dispatchDraw方法，這個方法在ViewGroup中有實現。
View或ViewGroup的子類不用再重載ViewGroup中該方法，由於它已經有了默認並且標準的view系統流程。dispatchDraw()內部for循環調用drawChild()分別繪製每個子視圖，而drawChild()內部又會調用draw（）函數完成子視圖的內部繪製工做。
/**
* {@inheritDoc}
*/
@Override
protected void dispatchDraw(Canvas canvas) {
final int count = mChildrenCount;
final View[] children = mChildren;
int flags = mGroupFlags;
if ((flags & FLAG_RUN_ANIMATION) != 0 && canAnimate()) {
final boolean cache = (mGroupFlags & FLAG_ANIMATION_CACHE) == FLAG_ANIMATION_CACHE;
final boolean buildCache = !isHardwareAccelerated();
for (int i = 0; i < count; i++) {
final View child = children[i];
if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE) {
final LayoutParams params = child.getLayoutParams();
attachLayoutAnimationParameters(child, params, i, count);
bindLayoutAnimation(child);
if (cache) {
child.setDrawingCacheEnabled(true);
if (buildCache) {
child.buildDrawingCache(true);
}
}
}
}
final LayoutAnimationController controller = mLayoutAnimationController;
if (controller.willOverlap()) {
mGroupFlags |= FLAG_OPTIMIZE_INVALIDATE;
}
controller.start();
mGroupFlags &= ~FLAG_RUN_ANIMATION;
mGroupFlags &= ~FLAG_ANIMATION_DONE;
if (cache) {
mGroupFlags |= FLAG_CHILDREN_DRAWN_WITH_CACHE;
}
if (mAnimationListener != null) {
mAnimationListener.onAnimationStart(controller.getAnimation());
}
}
int saveCount = 0;
final boolean clipToPadding = (flags & CLIP_TO_PADDING_MASK) == CLIP_TO_PADDING_MASK;
if (clipToPadding) {
saveCount = canvas.save();
canvas.clipRect(mScrollX + mPaddingLeft, mScrollY + mPaddingTop,
mScrollX + mRight - mLeft - mPaddingRight,
mScrollY + mBottom - mTop - mPaddingBottom);
}
// We will draw our child's animation, let's reset the flag
mPrivateFlags &= ~PFLAG_DRAW_ANIMATION;
mGroupFlags &= ~FLAG_INVALIDATE_REQUIRED;
boolean more = false;
final long drawingTime = getDrawingTime();
if ((flags & FLAG_USE_CHILD_DRAWING_ORDER) == 0) {
for (int i = 0; i < count; i++) {
final View child = children[i];
if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE || child.getAnimation() != null) {
more |= drawChild(canvas, child, drawingTime);
}
}
} else {
for (int i = 0; i < count; i++) {
final View child = children[getChildDrawingOrder(count, i)];
if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE || child.getAnimation() != null) {
more |= drawChild(canvas, child, drawingTime);
}
}
}
// Draw any disappearing views that have animations
if (mDisappearingChildren != null) {
final ArrayList<View> disappearingChildren = mDisappearingChildren;
final int disappearingCount = disappearingChildren.size() - 1;
// Go backwards -- we may delete as animations finish
for (int i = disappearingCount; i >= 0; i--) {
final View child = disappearingChildren.get(i);
more |= drawChild(canvas, child, drawingTime);
}
}
if (debugDraw()) {
onDebugDraw(canvas);
}
if (clipToPadding) {
canvas.restoreToCount(saveCount);
}
// mGroupFlags might have been updated by drawChild()
flags = mGroupFlags;
if ((flags & FLAG_INVALIDATE_REQUIRED) == FLAG_INVALIDATE_REQUIRED) {
invalidate(true);
}
if ((flags & FLAG_ANIMATION_DONE) == 0 && (flags & FLAG_NOTIFY_ANIMATION_LISTENER) == 0 &&
mLayoutAnimationController.isDone() && !more) {
// We want to erase the drawing cache and notify the listener after the
// next frame is drawn because one extra invalidate() is caused by
// drawChild() after the animation is over
mGroupFlags |= FLAG_NOTIFY_ANIMATION_LISTENER;
final Runnable end = new Runnable() {
public void run() {
notifyAnimationListener();
}
};
post(end);
}
}
上面基本介紹完了View的繪製流程。更多的細節須要在平常學習中總結。
/**
* @author 張興業
* http://blog.csdn.net/xyz_lmn
* 個人新浪微博：
@張興業TBOW
參考：
http://developer.android.com/guide/topics/ui/how-android-draws.html
http://www.2cto.com/kf/201312/267855.html相關文章
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相關文章
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