Android View.invalidate()&&postI

自定义view的时候，我们会在一些设置属性的方法最后调用invalidate()来刷新view。

下面看看源码实现。

• View.invalidate()

public void invalidate() {
        invalidate(true);
    }

//invalidateCache默认是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;
            }

            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);
                //关键点
                p.invalidateChild(this, damage);
            }

            if (mBackground != null && mBackground.isProjected()) {
                final View receiver = getProjectionReceiver();
                if (receiver != null) {
                    receiver.damageInParent();
                }
            }
        }
    }

重点p.invalidateChild(this, damage);
ViewParent ViewGroup或ViewRootImpl

ViewGroup也是调用ViewRootImpl.invalidateChildInParent()

public final void invalidateChild(View child, final Rect dirty) {
      ...
      do{
          ...
          parent = parent.invalidateChildInParent(location, dirty);
      }while (parent != null);
      ...
}

ViewRootImpl

public void invalidateChild(View child, Rect dirty) {
        invalidateChildInParent(null, dirty);
    }

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);
            }
        }

        invalidateRectOnScreen(dirty);

        return null;
    }

invalidateRectOnScreen()

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)) {
            scheduleTraversals();
        }
    }

scheduleTraversals()

void scheduleTraversals() {
        if (!mTraversalScheduled) {
            mTraversalScheduled = true;
            mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
            mChoreographer.postCallback(
                    Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
            if (!mUnbufferedInputDispatch) {
                scheduleConsumeBatchedInput();
            }
            notifyRendererOfFramePending();
            pokeDrawLockIfNeeded();
        }
    }

mHandler.getLooper().getQueue().postSyncBarrier();
这里开启了同步障碍，下面肯定进行ui绘制了。
mTraversalRunnable是TraversalRunnable实现了Runnable接口

TraversalRunnable

final class TraversalRunnable implements Runnable {
        @Override
        public void run() {
            doTraversal();
        }
    }

ViewRootImpl.doTraversal()

void doTraversal() {
        if (mTraversalScheduled) {
            mTraversalScheduled = false;
            mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);

            if (mProfile) {
                Debug.startMethodTracing("ViewAncestor");
            }
            //绘制
            performTraversals();

            if (mProfile) {
                Debug.stopMethodTracing();
                mProfile = false;
            }
        }
    }

总结就是View.invalidate()最终调用ViewRootImpl.performTraversals()方法完成ui刷新。

• View.postInvalidate() 子线程中调用

    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.dispatchInvalidateDelayed()

final ViewRootHandler mHandler = new ViewRootHandler();

    public void dispatchInvalidateDelayed(View view, long delayMilliseconds) {
        Message msg = mHandler.obtainMessage(MSG_INVALIDATE, view);
        mHandler.sendMessageDelayed(msg, delayMilliseconds);
    }

这里用hanlder发送消息MSG_INVALIDATE，看看ViewRootHandler的handleMessage方法。

public void handleMessage(Message msg) {
      ...
      switch (msg.what) {
                case MSG_INVALIDATE:
                    ((View) msg.obj).invalidate();
                    break;
                    ...
      }
      ...
}

最终还是调用View.invalidate()，只不过通过handler切换到了ui线程。