AppBarLayout&CoordinatorLayout&Behavior

標簽（空格分隔）： android

AppBarLayout

AppBarLayout繼承自vertical的Linearlayout

app:expanded="false"（setExpanded） 控制是折疊還是展開

addOnOffsetChangedListener可以監控vertical偏移量

內部view可以app:layout_scrollFlags控制滾動

scroll|exitUntilCollapsed 向上滑動以minHeight折疊在頂端，必須設置minHeight屬性
scroll|enterAlways|enterAlwaysCollapsed 快速返回，先以minHeight顯示，滾動控件下滑到頂端時，則可繼續滑動展開
scroll|enterAlways|exitUntilCollapsed 快速返回，向上滑動以minHeight折疊在頂端，必須設置minHeight屬性
snap 要嘛全部顯示要嘛全不顯示

主要源碼分析

//檢測ScrollInterpolator子view，刷新子view折疊狀態以minHeight @Override protected void onLayout(boolean changed, int l, int t, int r, int b) {super.onLayout(changed, l, t, r, b);//無效化滾動范圍invalidateScrollRanges();mHaveChildWithInterpolator = false;for (int i = 0, z = getChildCount(); i < z; i++) {final View child = getChildAt(i);final LayoutParams childLp = (LayoutParams) child.getLayoutParams();final Interpolator interpolator = childLp.getScrollInterpolator();if (interpolator != null) {mHaveChildWithInterpolator = true;break;}}updateCollapsible(); }private void updateCollapsible() {boolean haveCollapsibleChild = false;for (int i = 0, z = getChildCount(); i < z; i++) {if (((LayoutParams) getChildAt(i).getLayoutParams()).isCollapsible()) {haveCollapsibleChild = true;break;}}setCollapsibleState(haveCollapsibleChild); }AppBarLayout中的LayoutParams主要封裝了ScrollFlags（app:layout_scrollFlags）等相關//計算總的滾動范圍（也是預向上的滾動范圍getUpNestedPreScrollRange） public final int getTotalScrollRange() {if (mTotalScrollRange != INVALID_SCROLL_RANGE) {return mTotalScrollRange;}//順序遍歷，如果第一個子view沒有scroll，則直接退出了，后面的設置也將無效int range = 0;for (int i = 0, z = getChildCount(); i < z; i++) {final View child = getChildAt(i);final LayoutParams lp = (LayoutParams) child.getLayoutParams();final int childHeight = child.getMeasuredHeight();final int flags = lp.mScrollFlags;//從這里可以看出如果要實現滾動，則子控件必須包含scroll flag（app:layout_scrollFlags="scroll" or LayoutParams#setScrollFlags）if ((flags & LayoutParams.SCROLL_FLAG_SCROLL) != 0) {// We're set to scroll so add the child's heightrange += childHeight + lp.topMargin + lp.bottomMargin;//如果包含exitUntilCollapsed flag則減去該child view 的最小高度，所以設置了這個flag則滾動到到這個view為最小顯示高度止if ((flags & LayoutParams.SCROLL_FLAG_EXIT_UNTIL_COLLAPSED) != 0) {// For a collapsing scroll, we to take the collapsed height into account.// We also break straight away since later views can't scroll beneath// usrange -= ViewCompat.getMinimumHeight(child);break;}} else {// As soon as a view doesn't have the scroll flag, we end the range calculation.// This is because views below can not scroll under a fixed view.break;}}return mTotalScrollRange = Math.max(0, range - getTopInset()); }//預向下的滾動范圍 int getDownNestedPreScrollRange() {if (mDownPreScrollRange != INVALID_SCROLL_RANGE) {// If we already have a valid value, return itreturn mDownPreScrollRange;}//倒序遍歷，處理是否有快速返回模式。所以設置的效果只能體現在最后一個子view上//eg。第一個child view scroll|enterAlways，第二個child view scroll//向下滑動時快速返回的是第二個child viewint range = 0;for (int i = getChildCount() - 1; i >= 0; i--) {final View child = getChildAt(i);final LayoutParams lp = (LayoutParams) child.getLayoutParams();final int childHeight = child.getMeasuredHeight();final int flags = lp.mScrollFlags;//是否是快速返回模式 scroll|enterAlways//FLAG_QUICK_RETURN==SCROLL_FLAG_SCROLL | SCROLL_FLAG_ENTER_ALWAYSif ((flags & LayoutParams.FLAG_QUICK_RETURN) == LayoutParams.FLAG_QUICK_RETURN) {// First take the margin into accountrange += lp.topMargin + lp.bottomMargin;// The view has the quick return flag combination...//如果還是enterAlwaysCollapsed，則滾動范圍加上minHeight，即快速返回時不是全部高度是minHeight//scroll|enterAlways|enterAlwaysCollapsedif ((flags & LayoutParams.SCROLL_FLAG_ENTER_ALWAYS_COLLAPSED) != 0) {// If they're set to enter collapsed, use the minimum heightrange += ViewCompat.getMinimumHeight(child);} else if ((flags & LayoutParams.SCROLL_FLAG_EXIT_UNTIL_COLLAPSED) != 0) {// Only enter by the amount of the collapsed height//如果是exitUntilCollapsed，則最小高度不能夠被折疊//scroll|enterAlways|exitUntilCollapsedrange += childHeight - ViewCompat.getMinimumHeight(child);} else {// Else use the full heightrange += childHeight;}} else if (range > 0) {// If we've hit an non-quick return scrollable view, and we've already hit a// quick return view, return nowbreak;}}return mDownPreScrollRange = Math.max(0, range);}//向下滾動范圍 int getDownNestedScrollRange() {if (mDownScrollRange != INVALID_SCROLL_RANGE) {// If we already have a valid value, return itreturn mDownScrollRange;}int range = 0;for (int i = 0, z = getChildCount(); i < z; i++) {final View child = getChildAt(i);final LayoutParams lp = (LayoutParams) child.getLayoutParams();int childHeight = child.getMeasuredHeight();childHeight += lp.topMargin + lp.bottomMargin;final int flags = lp.mScrollFlags;//檢查是否有scroll標記if ((flags & LayoutParams.SCROLL_FLAG_SCROLL) != 0) {// We're set to scroll so add the child's heightrange += childHeight;//是否有exitUntilCollapsed標記，減去minHegihtif ((flags & LayoutParams.SCROLL_FLAG_EXIT_UNTIL_COLLAPSED) != 0) {// For a collapsing exit scroll, we to take the collapsed height into account.// We also break the range straight away since later views can't scroll// beneath usrange -= ViewCompat.getMinimumHeight(child) + getTopInset();break;}} else {// As soon as a view doesn't have the scroll flag, we end the range calculation.// This is because views below can not scroll under a fixed view.break;}}return mDownScrollRange = Math.max(0, range); }

CoordinatorLayout&Behavior

CoordinatorLayout繼承自ViewGroup

LayoutParams給child view提供了一系列屬性，app:layout_anchor設置錨點，app:layout_anchorGravity設置處于錨點什么位置，app:layout_behavior="@string/appbar_scrolling_view_behavior"指定behavior

主要源碼分析
首先實現Behavior必須保證存在Context，AttributeSet兩個參數的構造方法，內部利用反射獲取的Behavior。指定Behavior有2種方式
1. 利用xml中app:layout_behavior指定，取值為Behavior的全包名
2. 利用@CoordinatorLayout.DefaultBehavior注解指定

static final Class<?>[] CONSTRUCTOR_PARAMS = new Class<?>[] {Context.class,AttributeSet.class }; final Class<Behavior> clazz = (Class<Behavior>) Class.forName(fullName, true, context.getClassLoader()); c = clazz.getConstructor(CONSTRUCTOR_PARAMS);//獲取xml配置behavior mBehaviorResolved = a.hasValue(R.styleable.CoordinatorLayout_Layout_layout_behavior); if (mBehaviorResolved) {mBehavior = parseBehavior(context, attrs, a.getString(R.styleable.CoordinatorLayout_Layout_layout_behavior)); } //反射指定 LayoutParams getResolvedLayoutParams(View child) {final LayoutParams result = (LayoutParams) child.getLayoutParams();if (!result.mBehaviorResolved) {Class<?> childClass = child.getClass();DefaultBehavior defaultBehavior = null;while (childClass != null &&(defaultBehavior = childClass.getAnnotation(DefaultBehavior.class)) == null) {childClass = childClass.getSuperclass();}if (defaultBehavior != null) {try {result.setBehavior(defaultBehavior.value().newInstance());} catch (Exception e) {Log.e(TAG, "Default behavior class " + defaultBehavior.value().getName() +" could not be instantiated. Did you forget a default constructor?", e);}}result.mBehaviorResolved = true;}return result; }

綁定解綁Behavior到LayoutParams

//CoordinatorLayout.LayoutParams實例化完成后回調，setBehavior將引發回調 public void onAttachedToLayoutParams(@NonNull CoordinatorLayout.LayoutParams params) { }//從CoordinatorLayout子view解綁時調用 public void onDetachedFromLayoutParams() { }

CoordinatorLayouot初始化LayoutParams中回調綁定

if (mBehaviorResolved) {mBehavior = parseBehavior(context, attrs, a.getString(R.styleable.CoordinatorLayout_Layout_layout_behavior)); } a.recycle();if (mBehavior != null) {// If we have a Behavior, dispatch that it has been attachedmBehavior.onAttachedToLayoutParams(this); }

指定新的Behavior，解綁之前的并綁定新的

public void setBehavior(@Nullable Behavior behavior) {if (mBehavior != behavior) {if (mBehavior != null) {// First detach any old behaviormBehavior.onDetachedFromLayoutParams();}mBehavior = behavior;mBehaviorTag = null;mBehaviorResolved = true;if (behavior != null) {// Now dispatch that the Behavior has been attachedbehavior.onAttachedToLayoutParams(this);}} }

綁定后先確定依賴關系

//返回true確定依賴關系（可能調用多次） child 為behavior dependency為被依賴的view public boolean layoutDependsOn(CoordinatorLayout parent, V child, View dependency) {return false; }//依賴view發生變化時回調 public boolean onDependentViewChanged(CoordinatorLayout parent, V child, View dependency) {return false; }//依賴view移除時回調 public void onDependentViewRemoved(CoordinatorLayout parent, V child, View dependency) { }

在onMeasu中執行了prepareChildren方法確定了依賴關系，內部執行了LayoutParams的dependsOn，內部引用了Behavior的layoutDependsOn

private void prepareChildren() {//保存排序后的子視圖mDependencySortedChildren.clear();//有向無環圖排序mChildDag.clear();for (int i = 0, count = getChildCount(); i < count; i++) {final View view = getChildAt(i);//尋找behavior并返回LayoutParamsfinal LayoutParams lp = getResolvedLayoutParams(view);//尋找錨點viewlp.findAnchorView(this, view);//保存child viewmChildDag.addNode(view);// Now iterate again over the other children, adding any dependencies to the graph//添加依賴關系圖，方便隨后布局viewfor (int j = 0; j < count; j++) {if (j == i) {continue;}final View other = getChildAt(j);final LayoutParams otherLp = getResolvedLayoutParams(other);//返回true，確定依賴關系if (otherLp.dependsOn(this, other, view)) {if (!mChildDag.contains(other)) {// Make sure that the other node is addedmChildDag.addNode(other);}// Now add the dependency to the graphmChildDag.addEdge(view, other);}}}// Finally add the sorted graph list to our listmDependencySortedChildren.addAll(mChildDag.getSortedList());// We also need to reverse the result since we want the start of the list to contain// Views which have no dependencies, then dependent views after thatCollections.reverse(mDependencySortedChildren); }View findAnchorView(CoordinatorLayout parent, View forChild) {//沒有指定直接返回if (mAnchorId == View.NO_ID) {mAnchorView = mAnchorDirectChild = null;return null;}//如果錨點view為空或者通過setAnchorId更改了錨點view則if (mAnchorView == null || !verifyAnchorView(forChild, parent)) {//賦值錨點viewresolveAnchorView(forChild, parent);}return mAnchorView; }//檢驗錨點view是否還有效 private boolean verifyAnchorView(View forChild, CoordinatorLayout parent) {if (mAnchorView.getId() != mAnchorId) {return false;}View directChild = mAnchorView;for (ViewParent p = mAnchorView.getParent();p != parent;p = p.getParent()) {if (p == null || p == forChild) {mAnchorView = mAnchorDirectChild = null;return false;}if (p instanceof View) {directChild = (View) p;}}mAnchorDirectChild = directChild;return true; }//設置錨點view和錨點view CoordinatorLayout的直接子view private void resolveAnchorView(final View forChild, final CoordinatorLayout parent) {mAnchorView = parent.findViewById(mAnchorId);if (mAnchorView != null) {//錨點view不能為CoordinatorLayoutif (mAnchorView == parent) {if (parent.isInEditMode()) {mAnchorView = mAnchorDirectChild = null;return;}throw new IllegalStateException("View can not be anchored to the the parent CoordinatorLayout");}//如果錨點view是CoordinatorLayout的直接子view，直接結束。如果不是直接子view，則循環找到為止，同時從代碼中可以看出錨點view不能是一個層次結構的內部view，如：<LinearLayoutandroid:id="@+id/ll"android:layout_width="match_parent"android:layout_height="wrap_content"android:layout_gravity="bottom"app:layout_anchor="@+id/bind_ck"android:orientation="horizontal"><Buttonandroid:id="@+id/bind_ck"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="綁定ck并解綁tv"/></LinearLayout>View directChild = mAnchorView;for (ViewParent p = mAnchorView.getParent();p != parent && p != null;p = p.getParent()) {if (p == forChild) {if (parent.isInEditMode()) {mAnchorView = mAnchorDirectChild = null;return;}throw new IllegalStateException("Anchor must not be a descendant of the anchored view");}if (p instanceof View) {directChild = (View) p;}}//錨點view CoordinatorLayout的直接子viewmAnchorDirectChild = directChild;} else {if (parent.isInEditMode()) {mAnchorView = mAnchorDirectChild = null;return;}throw new IllegalStateException("Could not find CoordinatorLayout descendant view"+ " with id " + parent.getResources().getResourceName(mAnchorId)+ " to anchor view " + forChild);} }//回調Behavior的layoutDependsOn boolean dependsOn(CoordinatorLayout parent, View child, View dependency) {//dependency == mAnchorDirectChild永遠為false？return dependency == mAnchorDirectChild|| shouldDodge(dependency, ViewCompat.getLayoutDirection(parent))|| (mBehavior != null && mBehavior.layoutDependsOn(parent, child, dependency)); }

確定依賴關系后則是安排布局

//CoordinatorLayout onLayout中回調,自己控制度量，false使用默認的，true自定義 public boolean onMeasureChild(CoordinatorLayout parent, V child,int parentWidthMeasureSpec, int widthUsed,int parentHeightMeasureSpec, int heightUsed) {return false; } //child指Behavior控件，返回true則自定義Behavior，false使用默認的。CoordinatorLayout onLayout中回調，可以代理改變behavior，如修改文本 public boolean onLayoutChild(CoordinatorLayout parent, V child, int layoutDirection) {return false; } @Override protected void onLayout(boolean changed, int l, int t, int r, int b) {final int layoutDirection = ViewCompat.getLayoutDirection(this);final int childCount = mDependencySortedChildren.size();for (int i = 0; i < childCount; i++) {final View child = mDependencySortedChildren.get(i);final LayoutParams lp = (LayoutParams) child.getLayoutParams();final Behavior behavior = lp.getBehavior();//回調Behavior的onLayoutChildif (behavior == null || !behavior.onLayoutChild(this, child, layoutDirection)) {onLayoutChild(child, layoutDirection);}} }

聯動事件處理。CoordinatorLayout實現了NestedScrollingParent，在對應的回調方法中在傳遞給Behavior的同名方法處理

@Override public boolean onStartNestedScroll(View child, View target, int nestedScrollAxes) {boolean handled = false;final int childCount = getChildCount();for (int i = 0; i < childCount; i++) {final View view = getChildAt(i);final LayoutParams lp = (LayoutParams) view.getLayoutParams();final Behavior viewBehavior = lp.getBehavior();if (viewBehavior != null) {final boolean accepted = viewBehavior.onStartNestedScroll(this, view, child, target,nestedScrollAxes);handled |= accepted;lp.acceptNestedScroll(accepted);} else {lp.acceptNestedScroll(false);}}return handled; }

同時事件攔截和處理也會傳遞給Behavior處理，Behavior先于其它子view獲取到事件

ViewOffsetBehavior主要是處理移動

//先使用默認方式布局完成，后面通過setTopAndBottomOffset，setLeftAndRightOffset就可以實現view移動 @Override public boolean onLayoutChild(CoordinatorLayout parent, V child, int layoutDirection) {// First let lay the child outlayoutChild(parent, child, layoutDirection);if (mViewOffsetHelper == null) {mViewOffsetHelper = new ViewOffsetHelper(child);}mViewOffsetHelper.onViewLayout();if (mTempTopBottomOffset != 0) {mViewOffsetHelper.setTopAndBottomOffset(mTempTopBottomOffset);mTempTopBottomOffset = 0;}if (mTempLeftRightOffset != 0) {mViewOffsetHelper.setLeftAndRightOffset(mTempLeftRightOffset);mTempLeftRightOffset = 0;}return true; }

HeaderBehavior繼承自ViewOffsetBehavior，增加了對事件的處理。

@Override public boolean onInterceptTouchEvent(CoordinatorLayout parent, V child, MotionEvent ev) {if (mTouchSlop < 0) {mTouchSlop = ViewConfiguration.get(parent.getContext()).getScaledTouchSlop();}final int action = ev.getAction();// 如果已經開始了拖動則直接攔截if (action == MotionEvent.ACTION_MOVE && mIsBeingDragged) {return true;}switch (MotionEventCompat.getActionMasked(ev)) {//down先不攔截事件case MotionEvent.ACTION_DOWN: {mIsBeingDragged = false;final int x = (int) ev.getX();final int y = (int) ev.getY();//是否能拖動并且處于view內if (canDragView(child) && parent.isPointInChildBounds(child, x, y)) {mLastMotionY = y;mActivePointerId = ev.getPointerId(0);ensureVelocityTracker();}break;}//move如果達到要求，攔截case MotionEvent.ACTION_MOVE: {//沒有有效pointid直接結束final int activePointerId = mActivePointerId;if (activePointerId == INVALID_POINTER) {// If we don't have a valid id, the touch down wasn't on content.break;}final int pointerIndex = ev.findPointerIndex(activePointerId);if (pointerIndex == -1) {break;}//大于閥值則認為拖動，攔截final int y = (int) ev.getY(pointerIndex);final int yDiff = Math.abs(y - mLastMotionY);if (yDiff > mTouchSlop) {mIsBeingDragged = true;mLastMotionY = y;}break;}case MotionEvent.ACTION_CANCEL:case MotionEvent.ACTION_UP: {mIsBeingDragged = false;mActivePointerId = INVALID_POINTER;if (mVelocityTracker != null) {mVelocityTracker.recycle();mVelocityTracker = null;}break;}}if (mVelocityTracker != null) {mVelocityTracker.addMovement(ev);}return mIsBeingDragged; }

現在看具體的AppBarLayout#Behavior，CoordinatorLayout下的ns控件發起ns事件，CoordinatorLayout進行對應的ns事件回調。

@Override public boolean onStartNestedScroll(CoordinatorLayout parent, AppBarLayout child,View directTargetChild, View target, int nestedScrollAxes) {//如果是豎直方向的滾動，并且AppBarLayout內有可滾動控件（前面的滾動標記），并且滾動區域足夠大，如果不夠大，不協同處理。這就是為什么cl+apb，如果cl內沒有ns控件，或者ns不能有效滾動時apb 不能折疊的原因final boolean started = (nestedScrollAxes & ViewCompat.SCROLL_AXIS_VERTICAL) != 0&& child.hasScrollableChildren()&& parent.getHeight() - directTargetChild.getHeight() <= child.getHeight();if (started && mOffsetAnimator != null) {// Cancel any offset animationmOffsetAnimator.cancel();}// A new nested scroll has started so clear out the previous refmLastNestedScrollingChildRef = null;return started; }

后面都是根據計算出的范圍進行處理，eg

@Override public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child,View target, int dx, int dy, int[] consumed) {if (dy != 0 && !mSkipNestedPreScroll) {int min, max;if (dy < 0) {// We're scrolling downmin = -child.getTotalScrollRange();max = min + child.getDownNestedPreScrollRange();} else {// We're scrolling upmin = -child.getUpNestedPreScrollRange();max = 0;}consumed[1] = scroll(coordinatorLayout, child, dy, min, max);} }

最后簡單看下ScrollingViewBehavior,這就是為什么需要指定app:layout_behavior="@string/appbar_scrolling_view_behavior"的緣故。定位。

@Override public boolean layoutDependsOn(CoordinatorLayout parent, View child, View dependency) {// We depend on any AppBarLayoutsreturn dependency instanceof AppBarLayout; }@Override public boolean onDependentViewChanged(CoordinatorLayout parent, View child,View dependency) {offsetChildAsNeeded(parent, child, dependency);return false; }

總結

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