Android view中invalidate方法学习小节

/**
     * Invalidate the whole view. If the view is visible,
     * {@link #onDraw(android.graphics.Canvas)} will be called at some point in
     * the future. This must be called from a UI thread. To call from a non-UI thread,
     * call {@link #postInvalidate()}.
     */
    public void invalidate() {
        invalidate(true);
    }

view中的invalidate方法会调用invalidate（true）;

/**
     * This is where the invalidate() work actually happens. A full invalidate()
     * causes the drawing cache to be invalidated, but this function can be called with
     * invalidateCache set to false to skip that invalidation step for cases that do not
     * need it (for example, a component that remains at the same dimensions with the same
     * content).
     *
     * @param invalidateCache Whether the drawing cache for this view should be invalidated as
     * well. This is usually true for a full invalidate, but may be set to false if the
     * View's contents or dimensions have not changed.
     */
    void invalidate(boolean invalidateCache) {
        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 || isOpaque() != mLastIsOpaque) {
            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;
            //noinspection PointlessBooleanExpression,ConstantConditions
            if (!HardwareRenderer.RENDER_DIRTY_REGIONS) {
                if (p != null && ai != null && ai.mHardwareAccelerated) {
                    // fast-track for GL-enabled applications; just invalidate the whole hierarchy
                    // with a null dirty rect, which tells the ViewAncestor to redraw everything
                    p.invalidateChild(this, null);
                    return;
                }
            }

            if (p != null && ai != null) {
                final Rect r = ai.mTmpInvalRect;
                r.set(0, 0, mRight - mLeft, mBottom - mTop);
                // Don't call invalidate -- we don't want to internally scroll
                // our own bounds
                p.invalidateChild(this, r);
            }
        }
    }

最终都会执行mParent的invalidateChild(this, r);如果开启硬件加速的话，r=null，即重绘整个View，r代表需要绘制的区域，r.set方法的调用设置了需要绘制区域的长和高。

下面看一下invalidateChild()方法

/**
     * Don't call or override this method. It is used for the implementation of
     * the view hierarchy.
     */
    public final void invalidateChild(View child, final Rect dirty) {
        ViewParent parent = this;

        final AttachInfo attachInfo = mAttachInfo;
        if (attachInfo != null) {
            // If the child is drawing an animation, we want to copy this flag onto
            // ourselves and the parent to make sure the invalidate request goes
            // through
            final boolean drawAnimation = (child.mPrivateFlags & PFLAG_DRAW_ANIMATION)
                    == PFLAG_DRAW_ANIMATION;

            // Check whether the child that requests the invalidate is fully opaque
            // Views being animated or transformed are not considered opaque because we may
            // be invalidating their old position and need the parent to paint behind them.
            Matrix childMatrix = child.getMatrix();
            final boolean isOpaque = child.isOpaque() && !drawAnimation &&
                    child.getAnimation() == null && childMatrix.isIdentity();
            // Mark the child as dirty, using the appropriate flag
            // Make sure we do not set both flags at the same time
            int opaqueFlag = isOpaque ? PFLAG_DIRTY_OPAQUE : PFLAG_DIRTY;

            if (child.mLayerType != LAYER_TYPE_NONE) {
                mPrivateFlags |= PFLAG_INVALIDATED;
                mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;
                child.mLocalDirtyRect.union(dirty);
            }

            final int[] location = attachInfo.mInvalidateChildLocation;
            location[CHILD_LEFT_INDEX] = child.mLeft;
            location[CHILD_TOP_INDEX] = child.mTop;
            if (!childMatrix.isIdentity() ||
                    (mGroupFlags & ViewGroup.FLAG_SUPPORT_STATIC_TRANSFORMATIONS) != 0) {
                RectF boundingRect = attachInfo.mTmpTransformRect;
                boundingRect.set(dirty);
                Matrix transformMatrix;
                if ((mGroupFlags & ViewGroup.FLAG_SUPPORT_STATIC_TRANSFORMATIONS) != 0) {
                    Transformation t = attachInfo.mTmpTransformation;
                    boolean transformed = getChildStaticTransformation(child, t);
                    if (transformed) {
                        transformMatrix = attachInfo.mTmpMatrix;
                        transformMatrix.set(t.getMatrix());
                        if (!childMatrix.isIdentity()) {
                            transformMatrix.preConcat(childMatrix);
                        }
                    } else {
                        transformMatrix = childMatrix;
                    }
                } else {
                    transformMatrix = childMatrix;
                }
                transformMatrix.mapRect(boundingRect);
                dirty.set((int) (boundingRect.left - 0.5f),
                        (int) (boundingRect.top - 0.5f),
                        (int) (boundingRect.right + 0.5f),
                        (int) (boundingRect.bottom + 0.5f));
            }

            do {
                View view = null;
                if (parent instanceof View) {
                    view = (View) parent;
                }

                if (drawAnimation) {
                    if (view != null) {
                        view.mPrivateFlags |= PFLAG_DRAW_ANIMATION;
                    } else if (parent instanceof ViewRootImpl) {
                        ((ViewRootImpl) parent).mIsAnimating = true;
                    }
                }

                // If the parent is dirty opaque or not dirty, mark it dirty with the opaque
                // flag coming from the child that initiated the invalidate
                if (view != null) {
                    if ((view.mViewFlags & FADING_EDGE_MASK) != 0 &&
                            view.getSolidColor() == 0) {
                        opaqueFlag = PFLAG_DIRTY;
                    }
                    if ((view.mPrivateFlags & PFLAG_DIRTY_MASK) != PFLAG_DIRTY) {
                        view.mPrivateFlags = (view.mPrivateFlags & ~PFLAG_DIRTY_MASK) | opaqueFlag;
                    }
                }

                parent = parent.invalidateChildInParent(location, dirty);
                if (view != null) {
                    // Account for transform on current parent
                    Matrix m = view.getMatrix();
                    if (!m.isIdentity()) {
                        RectF boundingRect = attachInfo.mTmpTransformRect;
                        boundingRect.set(dirty);
                        m.mapRect(boundingRect);
                        dirty.set((int) (boundingRect.left - 0.5f),
                                (int) (boundingRect.top - 0.5f),
                                (int) (boundingRect.right + 0.5f),
                                (int) (boundingRect.bottom + 0.5f));
                    }
                }
            } while (parent != null);
        }
    }

location数组设置了要绘制区域（dirty）的距离当前视图的左边界和上边界的距离，然后重点在do，while循环。parent = parent.invalidateChildInParent(location, dirty);

/**
     * Don't call or override this method. It is used for the implementation of
     * the view hierarchy.
     *
     * This implementation returns null if this ViewGroup does not have a parent,
     * if this ViewGroup is already fully invalidated or if the dirty rectangle
     * does not intersect with this ViewGroup's bounds.
     */
    public ViewParent invalidateChildInParent(final int[] location, final Rect dirty) {
        if ((mPrivateFlags & PFLAG_DRAWN) == PFLAG_DRAWN ||
                (mPrivateFlags & PFLAG_DRAWING_CACHE_VALID) == PFLAG_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();
                    }
                }
                mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;

                location[CHILD_LEFT_INDEX] = left;
                location[CHILD_TOP_INDEX] = top;

                if (mLayerType != LAYER_TYPE_NONE) {
                    mPrivateFlags |= PFLAG_INVALIDATED;
                    mLocalDirtyRect.union(dirty);
                }

                return mParent;

            } else {
                mPrivateFlags &= ~PFLAG_DRAWN & ~PFLAG_DRAWING_CACHE_VALID;

                location[CHILD_LEFT_INDEX] = mLeft;
                location[CHILD_TOP_INDEX] = mTop;
                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);
                }

                if (mLayerType != LAYER_TYPE_NONE) {
                    mPrivateFlags |= PFLAG_INVALIDATED;
                    mLocalDirtyRect.union(dirty);
                }

                return mParent;
            }
        }

        return null;
    }

逻辑有点复杂，大概的思想就是循环计算dirty区域相对于俯视图的坐标，即先得到子视图的dirty的大小然后在父视图中根据子视图和子视图的dirty的大小计算这块dirty相对于父视图的位置，这里做了计算dirty.offset(location[CHILD_LEFT_INDEX] - mScrollX, location[CHILD_TOP_INDEX] - mScrollY);通过之前的do while循环，最终的到整块dirty区域相对于最外层view的位置。循环的最上层是ViewRoot。下面是ViewRoot的invalidateChildInParent

public ViewParent invalidateChildInParent(final int[] location, final Rect dirty) {
        invalidateChild(null, dirty);
        return null;
    }

最终会return null

public void invalidateChild(View child, Rect dirty) {
        checkThread();
        if (DEBUG_DRAW) Log.v(TAG, "Invalidate child: " + dirty);
        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);
            }
        }
        mDirty.union(dirty);
        if (!mWillDrawSoon) {
            scheduleTraversals();
        }
    }

checkTread检查是不是UI线程。不是UI线程则报异常。最后执行sheduleTraversals，scheduleTraversals会发送一个异步消息，最终调用performTraversals()执行重绘。