前言：項目中在開發吸頂布局的時候使用了CoordinatorLayout和AppBarLayout實作，布局包括CoordinatorLayout、CollapsingToolbarLayout 、AppBarLayout、ToolBar和RecyclerView這五個類，
但是給CollapsingToolbarLayout 添加了app:layout_scrollFlags=snap屬性之後，輕輕滑動的時候在snap閥值的地方會有一個卡頓的過程然後會繼續滑動到結束。
1.首先看下xml布局檔案：
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">
android:id="@+id/AppFragment_AppBarLayout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
app:layout_behavior="com.boco.whl.funddemo.module.adapter.behavior.WhlBehavior">
android:id="@+id/AppFragment_CollapsingToolbarLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:contentScrim="@color/colorPrimary"
app:layout_scrollFlags="scroll|exitUntilCollapsed|snap">
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_collapseMode="parallax"
app:layout_collapseParallaxMultiplier="0.7">
android:id="@+id/AppFragment_Toolbar"
android:layout_width="match_parent"
android:layout_height="76dp"
android:paddingTop="20dp"
app:layout_collapseMode="pin">
android:layout_width="match_parent"
android:layout_height="56dp">
android:id="@+id/MyFragment_recyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginBottom="20dp"
android:background="@android:color/white"
app:layout_behavior="@string/appbar_scrolling_view_behavior" />
重點是
1.AppBarLayout中增加如下命名空間：
app:layout_behavior="com.boco.whl.funddemo.module.adapter.behavior.WhlBehavior"；
用來解決滑動回彈的bug；
2.CollapsingToolBarLayout中增加如下命名空間：
app:layout_scrollFlags="scroll|exitUntilCollapsed|snap"；
(5個scrollFlag關聯源碼)
* The view will be scroll in direct relation to scroll events. This flag needs to be
* set for any of the other flags to take effect. If any sibling views
* before this one do not have this flag, then this value has no effect.
public static final int SCROLL_FLAG_SCROLL = 0x1;
* When exiting (scrolling off screen) the view will be scrolled until it is
* 'collapsed'. The collapsed height is defined by the view''s minimum height.
* @see ViewCompat#getMinimumHeight(View)
* @see View#setMinimumHeight(int)
public static final int SCROLL_FLAG_EXIT_UNTIL_COLLAPSED = 0x2;
* When entering (scrolling on screen) the view will scroll on any downwards
* scroll event, regardless of whether the scrolling view is also scrolling. This
* is commonly referred to as the 'quick return' pattern.
public static final int SCROLL_FLAG_ENTER_ALWAYS = 0x4;
* An additional flag for 'enterAlways' which modifies the returning view to
* only initially scroll back to it''s collapsed height. Once the scrolling view has
* reached the end of it''s scroll range, the remainder of this view will be scrolled
* into view. The collapsed height is defined by the view''s minimum height.
* @see ViewCompat#getMinimumHeight(View)
* @see View#setMinimumHeight(int)
public static final int SCROLL_FLAG_ENTER_ALWAYS_COLLAPSED = 0x8;
* Upon a scroll ending, if the view is only partially visible then it will be snapped
* and scrolled to it''s closest edge. For example, if the view only has it''s bottom 25%
* displayed, it will be scrolled off screen completely. Conversely, if it''s bottom 75% * is visible then it will be scrolled fully into view.
public static final int SCROLL_FLAG_SNAP = 0x10;
用來使ToolBarLayout滑動時有個緊貼效果
3.以及Recyclerview中增加如下命名空間：
app:layout_behavior="@string/appbar_scrolling_view_behavior"
用來綁定和AppBarLayout的關聯滾動效果；
2.解題思路：
1.前情提要:
AppBarLayout類結構：.png
其中Behavior類結構：.png
繼承關系如下：
1.public static class Behavior extends HeaderBehavior
2.abstract class HeaderBehavior extends ViewOffsetBehavior
3.class ViewOffsetBehavior extends CoordinatorLayout.Behavior
2.在AppBarLayout.Behavior中我們發現這個方法用來實作貼緊效果的
private void snapToChildIfNeeded(CoordinatorLayout coordinatorLayout, AppBarLayout abl) {
final int offset = getTopBottomOffsetForScrollingSibling();
final int offsetChildIndex = getChildIndexOnOffset(abl, offset);
if (offsetChildIndex >= 0) {
final View offsetChild = abl.getChildAt(offsetChildIndex);
final LayoutParams lp = (LayoutParams) offsetChild.getLayoutParams();
final int flags = lp.getScrollFlags();
if ((flags & LayoutParams.FLAG_SNAP) == LayoutParams.FLAG_SNAP) {
// We're set the snap, so animate the offset to the nearest edge
int snapTop = -offsetChild.getTop();
int snapBottom = -offsetChild.getBottom();
if (offsetChildIndex == abl.getChildCount() - 1) {
// If this is the last child, we need to take the top inset into account
snapBottom += abl.getTopInset();
}
if (checkFlag(flags, LayoutParams.SCROLL_FLAG_EXIT_UNTIL_COLLAPSED)) {
// If the view is set only exit until it is collapsed, we'll abide by that
snapBottom += ViewCompat.getMinimumHeight(offsetChild);
} else if (checkFlag(flags, LayoutParams.FLAG_QUICK_RETURN
| LayoutParams.SCROLL_FLAG_ENTER_ALWAYS)) {
// If it's set to always enter collapsed, it actually has two states. We
// select the state and then snap within the state
final int seam = snapBottom + ViewCompat.getMinimumHeight(offsetChild);
if (offset < seam) {
snapTop = seam;
} else {
snapBottom = seam;
}
}
final int newOffset = offset < (snapBottom + snapTop) / 2
? snapBottom
: snapTop;
animateOffsetTo(coordinatorLayout, abl,
MathUtils.clamp(newOffset, -abl.getTotalScrollRange(), 0), 0);
}
}
}
在兩個地方執行：
1.
@Override
void onFlingFinished(CoordinatorLayout parent, AppBarLayout layout) {
// At the end of a manual fling, check to see if we need to snap to the edge-child
snapToChildIfNeeded(parent, layout);
}
2.
@Override
public void onStopNestedScroll(CoordinatorLayout coordinatorLayout, AppBarLayout abl,
View target, int type) {
if (type == ViewCompat.TYPE_TOUCH) {
// If we haven't been flung then let's see if the current view has been set to snap
snapToChildIfNeeded(coordinatorLayout, abl);
}
// Keep a reference to the previous nested scrolling child
mLastNestedScrollingChildRef = new WeakReference<>(target);
}
明顯我們需要對第二種執行情況進行修改，使得正在滑動的時候不執行貼緊操作，實作方式就是繼承Behavior類重寫其onStopNestedScroll方法，判斷目前是否處于慣性滑動操作之中。
3.自定義Behevior源碼如下：
public class WhlBehavior extends AppBarLayout.Behavior {
private boolean isFlinging = false;
public WhlBehavior() {}
public WhlBehavior(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
public void onStopNestedScroll(CoordinatorLayout coordinatorLayout, AppBarLayout abl, View target, int type) {
//如果不是慣性滑動,讓他可以執行緊貼操作
if (!isFlinging) {
super.onStopNestedScroll(coordinatorLayout, abl, target, type);
}
}
@Override
public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target, int dx, int dy, int[] consumed, int type) {
super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed, type);
//type==1時處于非慣性滑動
if (type == 1) {
isFlinging = false;
}
}
@Override
public boolean onNestedFling(@NonNull CoordinatorLayout coordinatorLayout, @NonNull AppBarLayout child, @NonNull View target, float velocityX, float velocityY, boolean consumed) {
//慣性滑動的時候設定為true
isFlinging = true;
return super.onNestedFling(coordinatorLayout, child, target, velocityX, velocityY, consumed);
}
}
附上執行效果圖：
執行效果圖.gif