嵌套系列導(dǎo)航
- 1.淺析NestedScrolling嵌套滑動機(jī)制之基礎(chǔ)篇
- 2.淺析NestedScrolling嵌套滑動機(jī)制之實踐篇-仿寫?zhàn)I了么商家詳情頁
- 3.淺析NestedScrolling嵌套滑動機(jī)制之CoordinatorLayout.Behavior
- 4.淺析NestedScrolling嵌套滑動機(jī)制之實踐篇-自定義Behavior實現(xiàn)小米音樂歌手詳情
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概述
在前面《淺析NestedScrolling嵌套滑動機(jī)制之基礎(chǔ)篇》里的常見效果提到Behavior也是走NestedScrolling機(jī)制來實現(xiàn)各種神奇的滑動效果泳唠，它伴隨CoordinatorLayout在Revision 24.1.0的android.support.v4兼容包被引入，和CoordinatorLayout結(jié)合實現(xiàn)各個控件聯(lián)動，可以攔截代理CoordinatorLayout的測量、布局、WindowInsets躯肌、觸摸事件、嵌套滑動破衔。
Behavior簡介
Behavior是作用于 CoordinatorLayout的直接子View 的交互行為插件清女。一個Behavior 實現(xiàn)了用戶的一個或者多個交互行為，它們可能包括拖拽晰筛、滑動嫡丙、快滑或者其他一些手勢。
/**
* 泛型<V>是Behavior關(guān)聯(lián)的View
*/
public static abstract class Behavior<V extends View> {
/**
* 默認(rèn)構(gòu)造方法,用于注解的方式創(chuàng)建或者在代碼中創(chuàng)建
*/
public Behavior() {}
/**
* 用于xml解析layout_Behavior屬性的構(gòu)造方法,如果需要Behavior支持在xml中使用,則必須有此構(gòu)造方法
*/
public Behavior(Context context, AttributeSet attrs) {}
/**
* 在LayoutParams實例化后調(diào)用,或者在調(diào)用了LayoutParams.setBehavior(behavior)時調(diào)用.
*/
public void onAttachedToLayoutParams(@NonNull CoordinatorLayout.LayoutParams params) {}
/**
* 同上面onAttachedToLayoutParams相反
* 當(dāng)LayoutParams移除Behavior時調(diào)用,例如調(diào)用了LayoutParams.setBehavior(null).
* View被從View Tree中移除時不會調(diào)用此方法.
*/
public void onDetachedFromLayoutParams() {}
/**
* 在CoordinatorLayout分發(fā)給子View前攔截Touch事件
*/
public boolean onInterceptTouchEvent(CoordinatorLayout parent, V child, MotionEvent ev) {
return false;
}
/**
* 在CoordinatorLayout分發(fā)給子View前消費(fèi)Touch事件
*/
public boolean onTouchEvent(CoordinatorLayout parent, V child, MotionEvent ev) {
return false;
}
/**
* 阻斷此Behavior所關(guān)聯(lián)View下層的View的交互
*/
public boolean blocksInteractionBelow(CoordinatorLayout parent, V child) {
return getScrimOpacity(parent, child) > 0.f;
}
/**
* 當(dāng)blocksInteractionBelow返回為true時读第，CoordinatorLayout將會在View的上層繪制
* 一個屏蔽的getScrimColor()顏色來顯示無法進(jìn)行交互的區(qū)域
*/
@ColorInt
public int getScrimColor(CoordinatorLayout parent, V child) {
return Color.BLACK;
}
/**
* getScrimColor()繪制顏色的透明度
*/
@FloatRange(from = 0, to = 1)
public float getScrimOpacity(CoordinatorLayout parent, V child){
return 0.f;
}
/**
* 關(guān)聯(lián)的View和感興趣的View進(jìn)行依賴
*/
public boolean layoutDependsOn(CoordinatorLayout parent, V child, View dependency) {
return false;
}
/**
* 依賴View的位置曙博、大小改變時回調(diào)
*/
public boolean onDependentViewChanged(CoordinatorLayout parent, V child, View dependency) {
return false;
}
/**
* 依賴View從布局移除時回調(diào)
*/
public void onDependentViewRemoved(CoordinatorLayout parent, V child, View dependency) {}
/**
* 代理CoordinatorLayout子View的測量，注意這個子View是關(guān)聯(lián)了當(dāng)前Behavior,
* 返回true表示使用Behavior的*onMeasureChild()來測量參數(shù)里child的這個子View怜瞒，
* 返回false則使用*CoordinatorLayout的默認(rèn)測量子View的方法父泳。
*/
public boolean onMeasureChild(CoordinatorLayout parent, V child,
int parentWidthMeasureSpec, int widthUsed,
int parentHeightMeasureSpec, int heightUsed) {
return false;
}
/**
* 代理CoordinatorLayout子View的布局
* 返回true表示使用Behavior的onLayoutChild()來布局子View
* 返回false則使用CoordinatorLayout的默認(rèn)測量子View的方法。
*/
public boolean onLayoutChild(CoordinatorLayout parent, V child, int layoutDirection) {
return false;
}
/**
*代理消費(fèi)CoordinatorLayout的WindowInsets
*/
@NonNull
public WindowInsetsCompat onApplyWindowInsets(CoordinatorLayout coordinatorLayout,
V child, WindowInsetsCompat insets) {
return insets;
}
//以下是NestedScrolling相關(guān)方法//
@Deprecated
public boolean onStartNestedScroll(@NonNull CoordinatorLayout coordinatorLayout,
@NonNull V child, @NonNull View directTargetChild, @NonNull View target,
@ScrollAxis int axes) {
return false;
}
public boolean onStartNestedScroll(@NonNull CoordinatorLayout coordinatorLayout,
@NonNull V child, @NonNull View directTargetChild, @NonNull View target,
@ScrollAxis int axes, @NestedScrollType int type) {
if (type == ViewCompat.TYPE_TOUCH) {
return onStartNestedScroll(coordinatorLayout, child, directTargetChild,
target, axes);
}
return false;
}
@Deprecated
public void onNestedScrollAccepted(@NonNull CoordinatorLayout coordinatorLayout,
@NonNull V child, @NonNull View directTargetChild, @NonNull View target,
@ScrollAxis int axes) {
}
public void onNestedScrollAccepted(@NonNull CoordinatorLayout coordinatorLayout,
@NonNull V child, @NonNull View directTargetChild, @NonNull View target,
@ScrollAxis int axes, @NestedScrollType int type) {
if (type == ViewCompat.TYPE_TOUCH) {
onNestedScrollAccepted(coordinatorLayout, child, directTargetChild,
target, axes);
}
}
@Deprecated
public void onStopNestedScroll(@NonNull CoordinatorLayout coordinatorLayout,
@NonNull V child, @NonNull View target) {
}
public void onStopNestedScroll(@NonNull CoordinatorLayout coordinatorLayout,
@NonNull V child, @NonNull View target, @NestedScrollType int type) {
if (type == ViewCompat.TYPE_TOUCH) {
onStopNestedScroll(coordinatorLayout, child, target);
}
}
@Deprecated
public void onNestedScroll(@NonNull CoordinatorLayout coordinatorLayout, @NonNull V child,
@NonNull View target, int dxConsumed, int dyConsumed,
int dxUnconsumed, int dyUnconsumed) {
}
public void onNestedScroll(@NonNull CoordinatorLayout coordinatorLayout, @NonNull V child,
@NonNull View target, int dxConsumed, int dyConsumed,
int dxUnconsumed, int dyUnconsumed, @NestedScrollType int type) {
if (type == ViewCompat.TYPE_TOUCH) {
onNestedScroll(coordinatorLayout, child, target, dxConsumed, dyConsumed,
dxUnconsumed, dyUnconsumed);
}
}
@Deprecated
public void onNestedPreScroll(@NonNull CoordinatorLayout coordinatorLayout,
@NonNull V child, @NonNull View target, int dx, int dy, @NonNull int[] consumed) {
}
public void onNestedPreScroll(@NonNull CoordinatorLayout coordinatorLayout,
@NonNull V child, @NonNull View target, int dx, int dy, @NonNull int[] consumed,
@NestedScrollType int type) {
if (type == ViewCompat.TYPE_TOUCH) {
onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed);
}
}
public boolean onNestedFling(@NonNull CoordinatorLayout coordinatorLayout,
@NonNull V child, @NonNull View target, float velocityX, float velocityY,
boolean consumed) {
return false;
}
public boolean onNestedPreFling(@NonNull CoordinatorLayout coordinatorLayout,
@NonNull V child, @NonNull View target, float velocityX, float velocityY) {
return false;
}
//省略部分非常用方法
...
}
View設(shè)置Behavior
xml布局文件設(shè)置
<!-- 布局文件 -->
<android.support.design.widget.CoordinatorLayout>
<android.support.v4.widget.NestedScrollView
app:layout_behavior="@string/appbar_scrolling_view_behavior"/>
</android.support.design.widget.CoordinatorLayout>
<!-- values.xml -->
<string name="appbar_scrolling_view_behavior" translatable="false">
android.support.design.widget.AppBarLayout$ScrollingViewBehavior
</string>
在布局文件對CoordinatorLayout的直接子View添加app:layout_behavio屬性，屬性是Behavior類全限包名惠窄，你可以把值放在values文件里蒸眠，也可以直接寫在布局文件里。在CoordinatorLayout的parseBehavior()調(diào)用Behavior兩個參數(shù)的構(gòu)造方法創(chuàng)建杆融。
代碼動態(tài)設(shè)置
AppBarLayout.ScrollingViewBehavior behavior = new AppBarLayout.ScrollingViewBehavior();
CoordinatorLayout.LayoutParams params =(CoordinatorLayout.LayoutParams) view.getLayoutParams();
params.setBehavior(behavior);
注解方式
@CoordinatorLayout.DefaultBehavior(AppBarLayout.Behavior.class)
public class AppBarLayout extends LinearLayout {}
注意如果同時使用注解和xml布局文件為同一個view設(shè)置Behavior楞卡，生效的是注解方式的Behavior,若在自定義Behavior使用此方式需要一個無參的構(gòu)造函數(shù)，因為CoordinatorLayout在getResolvedLayoutParams()解析時調(diào)用反射Behavior的無參構(gòu)造函數(shù)創(chuàng)建擒贸，而這種注解方式在support27.1.0版本打上了@Deprecated過時標(biāo)簽臀晃。
接口實現(xiàn)返回
View實現(xiàn)CoordinatorLayout.AttachedBehavior接口并復(fù)寫getBehavior()返回Behavior觉渴。在CoordinatorLayout在getResolvedLayoutParams()解析時調(diào)用getBehavior()獲取Behavior介劫，然后調(diào)用CoordinatorLayout.LayoutParams.setBehavior()傳入。
public class MyLayout extends LinearLayout implements CoordinatorLayout.AttachedBehavior{
@NonNull
@Override
Behavior getBehavior(){
return new AppBarLayout.ScrollingViewBehavior()
};
}
Behavior中的代理
代理CoordinatorLayout子View的測量
Behavior的onMeasureChild()可以代理CoordinatorLayout子View的測量案淋，注意這個子View是關(guān)聯(lián)了當(dāng)前Behavior座韵，它的返回值為Boolean類型，返回true表示使用Behavior的onMeasureChild()來測量參數(shù)里child的這個子View踢京，返回false則使用CoordinatorLayout的默認(rèn)測量子View的方法誉碴。
//CoordinatorLayout.Behavior
public boolean onMeasureChild(CoordinatorLayout parent, V child,
int parentWidthMeasureSpec, int widthUsed,
int parentHeightMeasureSpec, int heightUsed) {
return false;
}
在CoordinatorLayout的onMeasure()里可以看出Behavior中的代理子View的測量：
//CoordinatorLayout
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
...
final int childCount = mDependencySortedChildren.size();
for (int i = 0; i < childCount; i++) {
final View child = mDependencySortedChildren.get(i);
...
final LayoutParams lp = (LayoutParams) child.getLayoutParams();
...
//Behavior判空檢測是否可以代理measure
final Behavior b = lp.getBehavior();
if (b == null || !b.onMeasureChild(this, child, childWidthMeasureSpec, keylineWidthUsed,
childHeightMeasureSpec, 0)) {
onMeasureChild(child, childWidthMeasureSpec, keylineWidthUsed,
childHeightMeasureSpec, 0);
}
...
}
}
代理CoordinatorLayout子View的布局
和上面類似，Behavior的onLayoutChild()可以代理CoordinatorLayout子View的布局瓣距，它的返回值為Boolean類型黔帕，返回true表示使用Behavior的onLayoutChild()來布局子View，返回false則使用CoordinatorLayout的默認(rèn)測量子View的方法蹈丸。
//CoordinatorLayout.Behavior
public boolean onLayoutChild(CoordinatorLayout parent, V child, int layoutDirection) {
return false;
}
在CoordinatorLayout的onLayout()里可以看出Behavior中的代理子View的布局：
//CoordinatorLayout
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
...
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();
//Behavior判空檢測是否可以代理layout
if (behavior == null || !behavior.onLayoutChild(this, child, layoutDirection)) {
onLayoutChild(child, layoutDirection);
}
}
}
代理CoordinatorLayout的WindowInsets
Behavior的onApplyWindowInsets()可以代理消費(fèi)CoordinatorLayout的WindowInsets成黄。
//CoordinatorLayout.Behavior
public WindowInsetsCompat onApplyWindowInsets(CoordinatorLayout coordinatorLayout,
V child, WindowInsetsCompat insets) {
return insets;
}
在CoordinatorLayout的onLayout()里可以看出Behavior中的消費(fèi)CoordinatorLayout的WindowInsets：
setFitsSystemWindows()->setupForInsets()->setWindowInsets()->dispatchApplyWindowInsetsToBehaviors()
//CoordinatorLayout
private WindowInsetsCompat dispatchApplyWindowInsetsToBehaviors(WindowInsetsCompat insets) {
...
for (int i = 0, z = getChildCount(); i < z; i++) {
final View child = getChildAt(i);
if (ViewCompat.getFitsSystemWindows(child)) {
final LayoutParams lp = (LayoutParams) child.getLayoutParams();
final Behavior b = lp.getBehavior();
if (b != null) {
// If the view has a behavior, let it try first
insets = b.onApplyWindowInsets(this, child, insets);
if (insets.isConsumed()) {
// If it consumed the insets, break
break;
}
}
}
}
return insets;
}
代理CoordinatorLayout的Touch事件
Behavior的onInterceptTouchEvent()、onTouchEvent()可以在CoordinatorLayout分發(fā)給子View前被攔截消費(fèi)逻杖，若Behavior攔截了來自CoordinatorLayout的Touch事件奋岁，CoordinatorLayout的各個子View自然就接受不到Touch事件，Behavior的blocksInteractionBelow()表示是否阻斷此Behavior所關(guān)聯(lián)View下層的View的交互荸百，則這個方法能影響Touch事件的攔截闻伶，若blocksInteractionBelow()為true時，getScrimOpacity()返回值大于0够话，CoordinatorLayout將會在View的上層繪制一個屏蔽的getScrimColor()顏色來顯示無法進(jìn)行交互的區(qū)域：
//CoordinatorLayout.Behavior
public boolean onInterceptTouchEvent(CoordinatorLayout parent, V child, MotionEvent ev) {
return false;
}
public boolean onTouchEvent(CoordinatorLayout parent, V child, MotionEvent ev) {
return false;
}
public boolean blocksInteractionBelow(CoordinatorLayout parent, V child) {
return getScrimOpacity(parent, child) > 0.f;
}
public float getScrimOpacity(CoordinatorLayout parent, V child) {
return 0.f;
}
public int getScrimColor(CoordinatorLayout parent, V child) {
return Color.BLACK;
}
接下來看看CoordinatorLayout的onInterceptTouchEvent()蓝翰、onTouchEvent()如何被Behavior代理：
//CoordinatorLayout
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
...
final boolean intercepted = performIntercept(ev, TYPE_ON_INTERCEPT);
...
return intercepted;
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
boolean handled = false;
boolean cancelSuper = false;
MotionEvent cancelEvent = null;
...
if (mBehaviorTouchView != null || (cancelSuper = performIntercept(ev, TYPE_ON_TOUCH))) {
// Safe since performIntercept guarantees that
// mBehaviorTouchView != null if it returns true
final LayoutParams lp = (LayoutParams) mBehaviorTouchView.getLayoutParams();
final Behavior b = lp.getBehavior();
//Behavior不為空，事件分發(fā)給Behavior
if (b != null) {
handled = b.onTouchEvent(this, mBehaviorTouchView, ev);
}
}
// Keep the super implementation correct(走CoordinatorLayout默認(rèn)方法)
if (mBehaviorTouchView == null) {
handled |= super.onTouchEvent(ev);
} else if (cancelSuper) {
if (cancelEvent == null) {
final long now = SystemClock.uptimeMillis();
cancelEvent = MotionEvent.obtain(now, now,
MotionEvent.ACTION_CANCEL, 0.0f, 0.0f, 0);
}
super.onTouchEvent(cancelEvent);
}
...
return handled;
}
private boolean performIntercept(MotionEvent ev, final int type) {
boolean intercepted = false;
//記錄是否Behavior的blocksInteractionBelow()返回true女嘲，根據(jù)這個標(biāo)
//識來給剩余遍歷的Behavior分發(fā)個CANCEL的MotionEvent
boolean newBlock = false;
MotionEvent cancelEvent = null;
final int action = ev.getActionMasked();
//根據(jù)View的層級由高到低排序畜份，儲放在臨時的容器
final List<View> topmostChildList = mTempList1;
getTopSortedChildren(topmostChildList);
//(先遍歷最外層View的Behavior的Touch事件代理)
// Let topmost child views inspect first
final int childCount = topmostChildList.size();
for (int i = 0; i < childCount; i++) {
final View child = topmostChildList.get(i);
final LayoutParams lp = (LayoutParams) child.getLayoutParams();
final Behavior b = lp.getBehavior();
//若Touch事件已經(jīng)被前面遍歷的Behavior攔截或者newBlock為true表示前面遍歷的Behavior已阻斷交互、且action不是DOWN時
//那么后面剩余遍歷的Behavior分發(fā)個CANCEL的MotionEvent
if ((intercepted || newBlock) && action != MotionEvent.ACTION_DOWN) {
// Cancel all behaviors beneath the one that intercepted.
// If the event is "down" then we don't have anything to cancel yet.
if (b != null) {
if (cancelEvent == null) {
final long now = SystemClock.uptimeMillis();
cancelEvent = MotionEvent.obtain(now, now,
MotionEvent.ACTION_CANCEL, 0.0f, 0.0f, 0);
}
switch (type) {
case TYPE_ON_INTERCEPT:
b.onInterceptTouchEvent(this, child, cancelEvent);
break;
case TYPE_ON_TOUCH:
b.onTouchEvent(this, child, cancelEvent);
break;
}
}
continue;
}
//沒有攔截Touch事件澡为，Behavior不為空漂坏，事件分發(fā)給Behavior
if (!intercepted && b != null) {
switch (type) {
case TYPE_ON_INTERCEPT:
intercepted = b.onInterceptTouchEvent(this, child, ev);
break;
case TYPE_ON_TOUCH:
intercepted = b.onTouchEvent(this, child, ev);
break;
}
//如果Behavior攔截了Touch事件，標(biāo)記其關(guān)聯(lián)的View
if (intercepted) {
mBehaviorTouchView = child;
}
}
// Don't keep going if we're not allowing interaction below this.
// Setting newBlock will make sure we cancel the rest of the behaviors.
final boolean wasBlocking = lp.didBlockInteraction();
final boolean isBlocking = lp.isBlockingInteractionBelow(this, child);
newBlock = isBlocking && !wasBlocking;
if (isBlocking && !newBlock) {
//這里要考慮onInterceptTouchEvent()進(jìn)入performIntercept()Behavior阻斷過，
//再到onTouchEvent()進(jìn)入performIntercept()就不必再遍歷
// Stop here since we don't have anything more to cancel - we already did
// when the behavior first started blocking things below this point.
break;
}
}
topmostChildList.clear();
return intercepted;
}
//CoordinatorLayout.LayoutParams
/**
* Behavior是否之前已經(jīng)阻斷過此Behavior所關(guān)聯(lián)View下層的View的交互
*/
boolean didBlockInteraction() {
if (mBehavior == null) {
mDidBlockInteraction = false;
}
return mDidBlockInteraction;
}
/**
* Behavior已經(jīng)阻斷過此Behavior所關(guān)聯(lián)View下層的View的交互返回true顶别，
* 否則返回調(diào)用Behavior的blocksInteractionBelow并記錄已阻斷過
*/
boolean isBlockingInteractionBelow(CoordinatorLayout parent, View child) {
if (mDidBlockInteraction) {
return true;
}
return mDidBlockInteraction |= mBehavior != null
? mBehavior.blocksInteractionBelow(parent, child)
: false;
}
CoordinatorLayout的onInterceptTouchEvent()執(zhí)行攔截主要邏輯在performIntercept()里：
- 1.首先根據(jù)子View的層級由高到低排序后按順序遍歷子View的Behavior谷徙；
- 2.在遍歷中先判斷Touch事件已經(jīng)被前面遍歷的Behavior攔截或者阻斷、且不是DOWN事件驯绎，若符合這些條件則給剩余遍歷的Behavior分發(fā)個CANCEL的MotionEvent完慧；
- 3.然后將根據(jù)參數(shù)type調(diào)用Behavior對應(yīng)的事件攔截、消費(fèi)的方法剩失，如果Behavior攔截了Touch事件則以變量mBehaviorTouchView記錄其關(guān)聯(lián)的View屈尼；
- 4.接著調(diào)用CoordinatorLayout.LayoutParams的兩個判斷阻斷交互方法用變量newBlock記錄Behavior的阻斷交互。
CoordinatorLayout的onTouchEvent()邏輯如下：
- 1.先判斷之前在onInterceptTouchEvent()是否有記錄mBehaviorTouchView拴孤，若有則直接調(diào)用Behavior的onTouchEvent()脾歧；若無則調(diào)用performIntercept()且返回值賦值變量cancelSuper；
- 2.若cancelSuper為true說明已有Behavior調(diào)用onTouchEvent()消費(fèi)Touch事件了并記錄mBehaviorTouchView,然后通過mBehaviorTouchView的LayoutParam 再次調(diào)用Behavior的onTouchEvent()（ps:雖然根據(jù)源碼注釋說在這調(diào)用performIntercept()返回true是為了確保mBehaviorTouchView不為空演熟，但按邏輯理解Behavior的onTouchEvent()被執(zhí)行2次）鞭执；
- 3.接著如果沒有Behavior做出攔截,則會調(diào)用父類的onTouchEvent()，如果沒則判讀前面的變量cancelSuper是否為true芒粹，若true則為了防止之前已經(jīng)給父類傳了事件給父類的onTouchEvent傳一個cancel事件兄纺。
這里小結(jié)一下：如果重寫B(tài)ehavior的onInterceptTouchEvent()、onTouchEvent()應(yīng)當(dāng)非常注意其邏輯在 CoordinatorLayout中onInterceptTouchEvent()化漆、onTouchEvent()的合理性估脆，因為在Behavior代理觸摸事件的處理顯得有點復(fù)雜而且繁瑣,而且會有大量的非正常的cancel事件出現(xiàn)。
代理CoordinatorLayout的嵌套滑動
CoordinatorLayout實現(xiàn)了NestedScrollingParent2接口并也覆寫兼容NestedScrollingParent座云，但它本身并沒有處理嵌套滑動而是全部給Behavior代理疙赠，Behavior代理嵌套滑動是通過NestedScrollingParent2、NestedScrollingParent對應(yīng)的方法多了兩個參數(shù)：一個是CoordinatorLayout疙教，一個是Behavior關(guān)聯(lián)的View棺聊。因為涉及到方法比較多，這里不宜展開贞谓，關(guān)于嵌套滑動可以參考我之前寫的的《淺析NestedScrolling嵌套滑動機(jī)制之基礎(chǔ)篇》
//CoordinatorLayout.Behavior
public void onNestedPreScroll(@NonNull CoordinatorLayout coordinatorLayout,
@NonNull V child, @NonNull View target, int dx, int dy, @NonNull int[] consumed,
@NestedScrollType int type) {
if (type == ViewCompat.TYPE_TOUCH) {
onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed);
}
}
@Deprecated
public void onNestedPreScroll(@NonNull CoordinatorLayout coordinatorLayout,
@NonNull V child, @NonNull View target, int dx, int dy, @NonNull int[] consumed) {
// Do nothing
}
接下來看看CoordinatorLayout的嵌套滑動讓Behavior代理限佩，這里分析只兩個方法，其他的方法十分類似：
//CoordinatorLayout
@Override
public boolean onStartNestedScroll(View child, View target, int axes, int type) {
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) {
//Behavior代理onStartNestedScroll
final boolean accepted = viewBehavior.onStartNestedScroll(this, view, child,
target, axes, type);
handled |= accepted;
//在Behavior關(guān)聯(lián)的View的LayoutParams記錄是否接受嵌套滑動
lp.setNestedScrollAccepted(type, accepted);
} else {
lp.setNestedScrollAccepted(type, false);
}
}
return handled;
}
//CoordinatorLayout.LayoutParams
void setNestedScrollAccepted(int type, boolean accept) {
switch (type) {
case ViewCompat.TYPE_TOUCH:
mDidAcceptNestedScrollTouch = accept;
break;
case ViewCompat.TYPE_NON_TOUCH:
mDidAcceptNestedScrollNonTouch = accept;
break;
}
}
在CoordinatorLayout的onStartNestedScroll()里遍歷子View裸弦，獲取子View的Behavior并調(diào)用onStartNestedScroll()并在LayoutParams記錄是否接受嵌套滑動祟同。
//CoordinatorLayout
@Override
public void onNestedPreScroll(View target, int dx, int dy, int[] consumed, int type) {
...
final int childCount = getChildCount();
for (int i = 0; i < childCount; i++) {
final View view = getChildAt(i);
...
final LayoutParams lp = (LayoutParams) view.getLayoutParams();
//判斷Behavior是否接受嵌套滑動
if (!lp.isNestedScrollAccepted(type)) {
continue;
}
final Behavior viewBehavior = lp.getBehavior();
if (viewBehavior != null) {
...
////Behavior代理onNestedPreScroll
viewBehavior.onNestedPreScroll(this, view, target, dx, dy, mTempIntPair, type);
...
}
}
...
}
在CoordinatorLayout的onNestedPreScroll()里遍歷子View，獲取子View的LayoutParams判斷Behavior是否接受嵌套滑動理疙，若接受則獲取子View的Behavior并調(diào)用onNestedPreScroll()晕城。
小結(jié)
Behavior很強(qiáng)大，但是一般而言子View的測量窖贤、布局這部分邏輯可以放在自定義View內(nèi)部處理砖顷，而CoordinatorLayout的分發(fā)WindowInsets贰锁、Touch事件給子View都有固定的順序，如果你在Behavior處理時應(yīng)該注意其邏輯在CoordinatorLayout的合理性滤蝠，沒必要為了使用Behavior而是用它豌熄，嵌套滑動在實現(xiàn)神奇滑動的效果卻是十分有用，也可以解耦自定義NestedScrollParent的邏輯物咳。
Behavior的View依賴關(guān)系
建立View之間的依賴關(guān)系
Behavior可以通過layoutDependsOn()讓其關(guān)聯(lián)的View和感興趣的View進(jìn)行依賴锣险，從而可以監(jiān)聽依賴View的位置、大小改變時回調(diào)onDependentViewChanged()览闰，依賴View從布局移除時回調(diào)onDependentViewRemoved()芯肤。
<android.support.design.widget.CoordinatorLayout>
<android.support.design.widget.AppBarLayout
android:id="@+id/app_bar"/>
<android.support.design.widget.FloatingActionButton
app:layout_anchor="@id/app_bar"
app:layout_anchorGravity="bottom|end"
/>
</android.support.design.widget.CoordinatorLayout>
還有一種就是在布局文件添加layout_anchor設(shè)置錨點來建立依賴關(guān)系，不過這種依賴關(guān)系 只能監(jiān)聽依賴View的位置压鉴、大小改變時回調(diào)onDependentViewChanged()崖咨。
//CoordinatorLayout.Behavior
/**
* 返回值表示child是否依賴dependency
*/
public boolean layoutDependsOn(CoordinatorLayout parent, V child,
View dependency) {
return false;
}
/**
* 返回值表示Behavior是否改變child的大小或者位置
*/
public boolean onDependentViewChanged(CoordinatorLayout parent, V child,
View dependency) {
return false;
}
public void onDependentViewRemoved(CoordinatorLayout parent, V child,
View dependency) {
}
排序View的依賴關(guān)系
CoordinatorLayout對View的依賴關(guān)系通過support包的DirectedAcyclicGraph有向無環(huán)圖進(jìn)行拓?fù)渑判颉?/p>
在圖論中，如果一個有向圖從任意頂點出發(fā)無法經(jīng)過若干條邊回到該點晴弃，則這個圖是一個有向無環(huán)圖（DAG,directed acyclic graph）--維基百科
在CoordinatorLayout的onMeasure()里的prepareChildren()就是對View依賴關(guān)系進(jìn)行排序:
private final List<View> mDependencySortedChildren = new ArrayList<>();
private final DirectedAcyclicGraph<View> mChildDag = new DirectedAcyclicGraph<>();
private void prepareChildren() {
mDependencySortedChildren.clear();
mChildDag.clear();
for (int i = 0, count = getChildCount(); i < count; i++) {
final View view = getChildAt(i);
//找到View的Anchor錨點
final LayoutParams lp = getResolvedLayoutParams(view);
lp.findAnchorView(this, view);
//將view當(dāng)節(jié)點添加進(jìn)有向無環(huán)圖
mChildDag.addNode(view);
// Now iterate again over the other children, adding any dependencies to the graph
for (int j = 0; j < count; j++) {
if (j == i) {
continue;
}
final View other = getChildAt(j);
if (lp.dependsOn(this, view, other)) {//判斷view與other是否存在的依賴關(guān)系
if (!mChildDag.contains(other)) {
//(如果other沒在圖里則添加才能確保view與other在圖建立依賴)
// Make sure that the other node is added
mChildDag.addNode(other);
}
//(將view與other在圖添加邊建立依賴)
// Now add the dependency to the graph
mChildDag.addEdge(other, view);
}
}
}
//(將圖節(jié)點以深度優(yōu)先排序的list存放在list容器里)
// Finally add the sorted graph list to our list
mDependencySortedChildren.addAll(mChildDag.getSortedList());
//(反轉(zhuǎn)list讓沒有依賴關(guān)系的view排在list的前面)
// 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 that
Collections.reverse(mDependencySortedChildren);
}
- 1.CoordinatorLayout遍歷遍歷子view掩幢，調(diào)用CoordinatorLayout.LayoutParams.findAnchorView()找到View的Anchor錨點逊拍，并將當(dāng)前view作為節(jié)點添加到有向無環(huán)圖里上鞠。
- 2.在循環(huán)里在開啟循環(huán)遍歷其他子View,通過CoordinatorLayout.LayoutParams.dependsOn()判斷與外層循環(huán)的view是否存在依賴關(guān)系，若有則建立在圖添加邊建立依賴芯丧。
- 3.兩層循壞執(zhí)行完后芍阎，將有向無環(huán)圖的節(jié)點以深度優(yōu)先排序的list存放在mDependencySortedChildren里，然后反轉(zhuǎn)mDependencySortedChildren讓沒有依賴關(guān)系的view排在list的前面缨恒。
Behavior依賴View回調(diào)觸發(fā)過程
Behavior的onDependentViewChanged()和onDependentViewRemoved()被觸發(fā)在CoordinatorLayout的onChildViewsChanged()谴咸，這方法type參數(shù)有三個值：EVENT_PRE_DRAW(依賴view繪制之前事件類型)、EVENT_NESTED_SCROLL(依賴view嵌套滑動事件類型)骗露、EVENT_VIEW_REMOVED(依賴view從布局移除事件類型)岭佳。
final void onChildViewsChanged(@DispatchChangeEvent final int type) {
...
final int childCount = mDependencySortedChildren.size();
...
for (int i = 0; i < childCount; i++) {
final View child = mDependencySortedChildren.get(i);
final LayoutParams lp = (LayoutParams) child.getLayoutParams();
...
for (int j = 0; j < i; j++) {
final View checkChild = mDependencySortedChildren.get(j);
if (lp.mAnchorDirectChild == checkChild) {
//檢測view的anchor錨點位置是否發(fā)生變化來調(diào)整依賴view的位置
offsetChildToAnchor(child, layoutDirection);
}
}
...
for (int j = i + 1; j < childCount; j++) {
final View checkChild = mDependencySortedChildren.get(j);
final LayoutParams checkLp = (LayoutParams) checkChild.getLayoutParams();
final Behavior b = checkLp.getBehavior();
//判斷checkChild是否依賴child
if (b != null && b.layoutDependsOn(this, checkChild, child)) {
...
final boolean handled;
switch (type) {
case EVENT_VIEW_REMOVED:
//(分發(fā)依賴view從布局移除事件給Behavior)
b.onDependentViewRemoved(this, checkChild, child);
handled = true;
break;
default:
//(分發(fā)依賴view繪制之前事件或嵌套滑動事件給Behavior)
handled = b.onDependentViewChanged(this, checkChild, child);
break;
}
}
}
}
...
}
void offsetChildToAnchor(View child, int layoutDirection) {
...
//注意：這里view和anchor錨點位置都調(diào)整了，將這變化通知給Behavior
// If we have needed to move, make sure to notify the child's Behavior
final Behavior b = lp.getBehavior();
if (b != null) {
b.onDependentViewChanged(this, child, lp.mAnchorView);
}
...
}
在CoordinatorLayout的onNestedFling()萧锉、onNestedPreScroll()珊随、onNestedPreScroll()里如果NestedScrollingChild處理了嵌套滑動都會通過onChildViewsChanged(EVENT_NESTED_SCROLL)將依賴view嵌套滑動事件分發(fā)給Behavior,下面以onNestedScroll代碼為例。
//CoordiantorLayout.java
@Override
public void onNestedScroll(View target, int dxConsumed, int dyConsumed,
int dxUnconsumed, int dyUnconsumed, int type) {
...
if (accepted) {
onChildViewsChanged(EVENT_NESTED_SCROLL);
}
}
在CoordinatorLayout的構(gòu)造方法里通過setOnHierarchyChangeListener()注冊O(shè)nHierarchyChangeListener監(jiān)聽添加或移除View的層級變化柿隙，而CoordinatorLayout.OnHierarchyChangeListener在View被移除回調(diào)中調(diào)用onChildViewsChanged(EVENT_VIEW_REMOVED)將依賴view從布局移除事件類型分發(fā)給Behavior叶洞。
public CoordinatorLayout(Context context, AttributeSet attrs, int defStyleAttr) {
...
super.setOnHierarchyChangeListener(new HierarchyChangeListener();
}
private class HierarchyChangeListener implements OnHierarchyChangeListener {
...
@Override
public void onChildViewRemoved(View parent, View child) {
//將依賴view從布局移除事件類型分發(fā)給Behavior
onChildViewsChanged(EVENT_VIEW_REMOVED);
...
}
}
在CoordinatorLayout的onAttachedToWindow()中往ViewTreeObserver注冊個CoordinatorLayout.OnPreDrawListener，它會在每次刷新確定各View大小位置后并繪制之前回調(diào)禀崖，而在回調(diào)里調(diào)用onChildViewsChanged()將依賴view繪制之前事件類型分發(fā)給對應(yīng)的Behavior衩辟。
//是否需要注冊mOnPreDrawListener標(biāo)識
private boolean mNeedsPreDrawListener;
//是否已經(jīng)執(zhí)行onAttachedToWindow()標(biāo)識
private boolean mIsAttachedToWindow;
private OnPreDrawListener mOnPreDrawListener;
@Override
public void onAttachedToWindow() {
...
if (mNeedsPreDrawListener) {
if (mOnPreDrawListener == null) {
mOnPreDrawListener = new OnPreDrawListener();
}
final ViewTreeObserver vto = getViewTreeObserver();
vto.addOnPreDrawListener(mOnPreDrawListener);
}
...
mIsAttachedToWindow = true;
}
class OnPreDrawListener implements ViewTreeObserver.OnPreDrawListener {
@Override
public boolean onPreDraw() {
//分發(fā)依賴view繪制之前事件類型
onChildViewsChanged(EVENT_PRE_DRAW);
return true;
}
雖然onAttachedToWindow()會被調(diào)用在onDraw()之前，但也可能在onMeasure()之前調(diào)用波附，如果View之間不存在依賴關(guān)系則mOnPreDrawListener從ViewTree移除防止內(nèi)存泄露艺晴，所以在onMeasure()的ensurePreDrawListener()里檢測View之間是否存在依賴關(guān)系對mOnPreDrawListener進(jìn)行注冊或注銷昼钻。
void ensurePreDrawListener() {
boolean hasDependencies = false;
final int childCount = getChildCount();
//遍歷子View，看它們是否存在依賴關(guān)系
for (int i = 0; i < childCount; i++) {
final View child = getChildAt(i);
if (hasDependencies(child)) {
hasDependencies = true;
break;
}
}
if (hasDependencies != mNeedsPreDrawListener) {
if (hasDependencies) {
//存在依賴封寞，注冊mOnPreDrawListener
addPreDrawListener();
} else {
////不存在依賴换吧，注銷mOnPreDrawListener
removePreDrawListener();
}
}
}
void addPreDrawListener() {
//如果已經(jīng)執(zhí)行onAttachedToWindow()
if (mIsAttachedToWindow) {
// Add the listener
if (mOnPreDrawListener == null) {
mOnPreDrawListener = new OnPreDrawListener();
}
final ViewTreeObserver vto = getViewTreeObserver();
vto.addOnPreDrawListener(mOnPreDrawListener);
}
//(因為onMeasure()與onAttachedToWindow()調(diào)用順序不確定，
//所以這里標(biāo)識mNeedsPreDrawListener變量來處理注冊mOnPreDrawListener)
// Record that we need the listener regardless of whether or not we're attached.
// We'll add the real listener when we become attached.
mNeedsPreDrawListener = true;
}
void removePreDrawListener() {
if (mIsAttachedToWindow) {
if (mOnPreDrawListener != null) {
final ViewTreeObserver vto = getViewTreeObserver();
vto.removeOnPreDrawListener(mOnPreDrawListener);
}
}
mNeedsPreDrawListener = false;
}
}
自定義Behavior
-
1.在自定義Behavior之前您可以參考系統(tǒng)自帶的Behavior能否滿足需求钥星，如FloatActionButton內(nèi)部的Behavior能保證Snackbar彈出的時候不被FAB遮擋等：
Behavior繼承樹 2.是否有必要為子View的測量沾瓦、布局、分發(fā)WindowInsets和Touch事件而使用CoordinatorLayout+Behavior谦炒，這部分邏輯是否可以放在自定義View內(nèi)部處理贯莺。
-
3.Behavior的View依賴關(guān)系與NestedScrolling結(jié)合實現(xiàn)滑動更為方便。
image
image
上圖是我之前寫過的《淺析NestedScrolling嵌套滑動機(jī)制之實踐篇-仿寫?zhàn)I了么商家詳情頁》效果宁改，如果改成通過自定義Behavior實現(xiàn)思路：Content部分處理嵌套滑動邏輯缕探，而Header部分、Collapse Content部分还蹲、TopBar部分爹耗、Shop Bar部分通過Behavior.layoutDependsOn()都與Content部分建立依賴，監(jiān)聽Content部分的滑動回調(diào)Behavior.onDependentViewChanged()進(jìn)行各自部分的動畫谜喊、alpha潭兽、Transition等效果，相對于之前自定義View斗遏，這種實現(xiàn)邏輯更加解耦清晰山卦。
總結(jié)
CoordinatorLayout和Behavior結(jié)合很強(qiáng)大，但本文偏向概念性內(nèi)容诵次，難免有些枯燥账蓉，下篇文章實踐自定義Behavior，由于本人水平有限僅給各位提供參考逾一，希望能夠拋磚引玉铸本，如果有什么可以討論的問題可以在評論區(qū)留言或聯(lián)系本人。
