浅谈Android invalidate 分析

public void postInvalidate() {    postInvalidateDelayed(0);  }  public void postInvalidateDelayed(long delayMilliseconds) {    // We try only with the AttachInfo because there's no point in invalidating    // if we are not attached to our window    final AttachInfo attachInfo = mAttachInfo;    if (attachInfo != null) {      attachInfo.mViewRootImpl.dispatchInvalidateDelayed(this, delayMilliseconds);    }  }  // ViewRootImpl 中  public void dispatchInvalidateDelayed(View view, long delayMilliseconds) {    Message msg = mHandler.obtainMessage(MSG_INVALIDATE, view);    mHandler.sendMessageDelayed(msg, delayMilliseconds);  }  final class ViewRootHandler extends Handler {    @Override    public void handleMessage(Message msg) {      switch (msg.what) {      case MSG_INVALIDATE:        ((View) msg.obj).invalidate();        break;      ...    }

public class MainActivity extends Activity {  private TextView tvText;  @Override  public void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    tvText = (TextView) findViewById(R.id.main_tv);    new Thread(new Runnable() {      @Override      public void run() {        try {          Thread.sleep(200);        } catch (InterruptedException e) {          e.printStackTrace();        }        tvText.setText("OtherThread");      }    }).start();  }}

// ActivityThread 中  final void handleResumeActivity(IBinder token,      boolean clearHide, boolean isForward, boolean reallyResume, int seq, String reason) {    ActivityClientRecord r = mActivities.get(token);    ...    if (r != null) {      final Activity a = r.activity;      if (r.window == null && !a.mFinished && willBeVisible) {        r.window = r.activity.getWindow();        View decor = r.window.getDecorView();        decor.setVisibility(View.INVISIBLE);        ViewManager wm = a.getWindowManager();        WindowManager.LayoutParams l = r.window.getAttributes();        ...        if (a.mVisibleFromClient) {          if (!a.mWindowAdded) {            a.mWindowAdded = true;            // 关键代码            wm.addView(decor, l);          } else {            a.onWindowAttributesChanged(l);          }        }        ...  }  // WindowManagerGlobal 中  public void addView(View view, ViewGroup.LayoutParams params,      Display display, Window parentWindow) {    ...    ViewRootImpl root;    View panelParentView = null;    synchronized (mLock) {      ...      // 在这里创建 ViewRootImpl      root = new ViewRootImpl(view.getContext(), display);      view.setLayoutParams(wparams);      ...    }  }  // 在 ViewRootImpl 中有这么段代码，所有更新 UI 都会走到这里  void checkThread() {    if (mThread != Thread.currentThread()) { // mThread 就是主线程      throw new CalledFromWrongThreadException(          "Only the original thread that created a view hierarchy can touch its views.");    }  }

// view 中  public void invalidate() {    invalidate(true);  }  public void invalidate(boolean invalidateCache) {    invalidateInternal(0, 0, mRight - mLeft, mBottom - mTop, invalidateCache, true);  }  void invalidateInternal(int l, int t, int r, int b, boolean invalidateCache,      boolean fullInvalidate) {    if (mGhostView != null) {      mGhostView.invalidate(true);      return;    }    if (skipInvalidate()) {      return;    }    if ((mPrivateFlags & (PFLAG_DRAWN | PFLAG_HAS_BOUNDS)) == (PFLAG_DRAWN | PFLAG_HAS_BOUNDS)        || (invalidateCache && (mPrivateFlags & PFLAG_DRAWING_CACHE_VALID) == PFLAG_DRAWING_CACHE_VALID)        || (mPrivateFlags & PFLAG_INVALIDATED) != PFLAG_INVALIDATED        || (fullInvalidate && isOpaque() != mLastIsOpaque)) {      if (fullInvalidate) {        mLastIsOpaque = isOpaque();        mPrivateFlags &= ~PFLAG_DRAWN;      }      mPrivateFlags |= PFLAG_DIRTY;      if (invalidateCache) {        mPrivateFlags |= PFLAG_INVALIDATED;        mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;      }      // Propagate the damage rectangle to the parent view.      final AttachInfo ai = mAttachInfo;      final ViewParent p = mParent;      if (p != null && ai != null && l < r && t < b) {        final Rect damage = ai.mTmpInvalRect;        damage.set(l, t, r, b);        // 调用父类的 invalidateChild 方法        p.invalidateChild(this, damage);      }      // Damage the entire projection receiver, if necessary.      if (mBackground != null && mBackground.isProjected()) {        final View receiver = getProjectionReceiver();        if (receiver != null) {          receiver.damageInParent();        }      }    }  }

// ViewGroup 中  @Override  public final void invalidateChild(View child, final Rect dirty) {    final AttachInfo attachInfo = mAttachInfo;    ...    ViewParent parent = this;      do {        View view = null;        ...        // 关键代码        parent = parent.invalidateChildInParent(location, dirty);        ...    } while (parent != null);  }  @Override  public ViewParent invalidateChildInParent(final int[] location, final Rect dirty) {    if ((mPrivateFlags & (PFLAG_DRAWN | PFLAG_DRAWING_CACHE_VALID)) != 0) {      // either DRAWN, or DRAWING_CACHE_VALID      if ((mGroupFlags & (FLAG_OPTIMIZE_INVALIDATE | FLAG_ANIMATION_DONE))          != FLAG_OPTIMIZE_INVALIDATE) {        dirty.offset(location[CHILD_LEFT_INDEX] - mScrollX,            location[CHILD_TOP_INDEX] - mScrollY);        if ((mGroupFlags & FLAG_CLIP_CHILDREN) == 0) {          dirty.union(0, 0, mRight - mLeft, mBottom - mTop);        }        final int left = mLeft;        final int top = mTop;        if ((mGroupFlags & FLAG_CLIP_CHILDREN) == FLAG_CLIP_CHILDREN) {          if (!dirty.intersect(0, 0, mRight - left, mBottom - top)) {            dirty.setEmpty();          }        }        location[CHILD_LEFT_INDEX] = left;        location[CHILD_TOP_INDEX] = top;      } else {        if ((mGroupFlags & FLAG_CLIP_CHILDREN) == FLAG_CLIP_CHILDREN) {          dirty.set(0, 0, mRight - mLeft, mBottom - mTop);        } else {          // in case the dirty rect extends outside the bounds of this container          dirty.union(0, 0, mRight - mLeft, mBottom - mTop);        }        location[CHILD_LEFT_INDEX] = mLeft;        location[CHILD_TOP_INDEX] = mTop;        mPrivateFlags &= ~PFLAG_DRAWN;      }      mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;      if (mLayerType != LAYER_TYPE_NONE) {        mPrivateFlags |= PFLAG_INVALIDATED;      }      return mParent;    }    return null;  }

// ViewRootImpl 中  @Override  public ViewParent invalidateChildInParent(int[] location, Rect dirty) {    checkThread();    if (DEBUG_DRAW) Log.v(mTag, "Invalidate child: " + dirty);    if (dirty == null) {      invalidate();      return null;    } else if (dirty.isEmpty() && !mIsAnimating) {      return null;    }    if (mCurScrollY != 0 || mTranslator != null) {      mTempRect.set(dirty);      dirty = mTempRect;      if (mCurScrollY != 0) {        dirty.offset(0, -mCurScrollY);      }      if (mTranslator != null) {        mTranslator.translateRectInAppWindowToScreen(dirty);      }      if (mAttachInfo.mScalingRequired) {        dirty.inset(-1, -1);      }    }    // 又调用了这个方法    invalidateRectOnScreen(dirty);    return null;  }  private void invalidateRectOnScreen(Rect dirty) {    final Rect localDirty = mDirty;    if (!localDirty.isEmpty() && !localDirty.contains(dirty)) {      mAttachInfo.mSetIgnoreDirtyState = true;      mAttachInfo.mIgnoreDirtyState = true;    }    // Add the new dirty rect to the current one    localDirty.union(dirty.left, dirty.top, dirty.right, dirty.bottom);    // Intersect with the bounds of the window to skip    // updates that lie outside of the visible region    final float appScale = mAttachInfo.mApplicationScale;    final boolean intersected = localDirty.intersect(0, 0,        (int) (mWidth * appScale + 0.5f), (int) (mHeight * appScale + 0.5f));    if (!intersected) {      localDirty.setEmpty();    }    if (!mWillDrawSoon && (intersected || mIsAnimating)) {      // 关键又调用了这个方法      scheduleTraversals();    }  }  void scheduleTraversals() {    if (!mTraversalScheduled) {      mTraversalScheduled = true;      mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();      // 会调用 mTraversalRunnable 中的 run 方法      mChoreographer.postCallback(          Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);      if (!mUnbufferedInputDispatch) {        scheduleConsumeBatchedInput();      }      notifyRendererOfFramePending();      pokeDrawLockIfNeeded();    }  }  final class TraversalRunnable implements Runnable {    @Override    public void run() {      doTraversal();    }  }  void doTraversal() {    if (mTraversalScheduled) {      mTraversalScheduled = false;      mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);      if (mProfile) {        Debug.startMethodTracing("ViewAncestor");      }      // 终于到了关键方法了：      performTraversals();      if (mProfile) {        Debug.stopMethodTracing();        mProfile = false;      }    }  }

private void performTraversals() {    ...      // 这里最终会触发 view 的 onMeasure      performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);      performLayout(lp, mWidth, mHeight);      performDraw();    ...    mIsInTraversal = false;  }

private void performDraw() {    ...    try {      draw(fullRedrawNeeded);    } finally {      mIsDrawing = false;      Trace.traceEnd(Trace.TRACE_TAG_VIEW);    }    ...  }  private void draw(boolean fullRedrawNeeded) {    if (!drawSoftware(surface, mAttachInfo, xOffset, yOffset, scalingRequired, dirty)) {      return;    }  }  private boolean drawSoftware(Surface surface, AttachInfo attachInfo, int xoff, int yoff,      boolean scalingRequired, Rect dirty) {      ...      try {        canvas.translate(-xoff, -yoff);        if (mTranslator != null) {          mTranslator.translateCanvas(canvas);        }        canvas.setScreenDensity(scalingRequired ? mNoncompatDensity : 0);        attachInfo.mSetIgnoreDirtyState = false;        // 最终调用了 View 的 draw 方法了        mView.draw(canvas);       } finally {        ...      }    return true;  }

// View 中的 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) {      drawBackground(canvas);    }    // 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);      drawAutofilledHighlight(canvas);      // Overlay is part of the content and draws beneath Foreground      if (mOverlay != null && !mOverlay.isEmpty()) {        mOverlay.getOverlayView().dispatchDraw(canvas);      }      // Step 6, draw decorations (foreground, scrollbars)      onDrawForeground(canvas);      // Step 7, draw the default focus highlight      drawDefaultFocusHighlight(canvas);      if (debugDraw()) {        debugDrawFocus(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);      p.setShader(fade);      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);      p.setShader(fade);      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);      p.setShader(fade);      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);      p.setShader(fade);      canvas.drawRect(right - length, top, right, bottom, p);    }    canvas.restoreToCount(saveCount);    drawAutofilledHighlight(canvas);    // Overlay is part of the content and draws beneath Foreground    if (mOverlay != null && !mOverlay.isEmpty()) {      mOverlay.getOverlayView().dispatchDraw(canvas);    }    // Step 6, draw decorations (foreground, scrollbars)    onDrawForeground(canvas);  }

@Override  public void draw(Canvas canvas) {    ...    drawBackground(canvas); // 绘制背景    onDraw(canvas); // 调用自己的 onDraw 方法来绘制内容    dispatchDraw(canvas); // 分发绘制    onDrawForeground(canvas); // 绘制前景    ...  }

// View 中的实现，是个空方法，也就是 View 没有孩子，不需要什么分发  protected void dispatchDraw(Canvas canvas) {  }

@Override  protected void dispatchDraw(Canvas canvas) {    ...    while (transientIndex >= 0) {      // there may be additional transient views after the normal views      final View transientChild = mTransientViews.get(transientIndex);      if ((transientChild.mViewFlags & VISIBILITY_MASK) == VISIBLE ||          transientChild.getAnimation() != null) {        // 看到这里，会去绘制 子View        more |= drawChild(canvas, transientChild, drawingTime);      }      transientIndex++;      if (transientIndex >= transientCount) {        break;      }    }    ...  }  protected boolean drawChild(Canvas canvas, View child, long drawingTime) {    // 又调回了 View 的 draw 来了    return child.draw(canvas, this, drawingTime);  }