CoordinatorLayout和AppBarLayout海拔

Question

我創建了一個AppBar佈局這樣

<android.support.design.widget.AppBarLayout 
    xmlns:app="http://schemas.android.com/apk/res-auto" 
    xmlns:android="http://schemas.android.com/apk/res/android" 
    android:id="@+id/appbar_layout" 
    android:layout_height="@dimen/app_bar_height" 
    android:layout_width="match_parent" 
    android:fitsSystemWindows="true" 
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar" 
    app:elevation="20dp"> 

    <android.support.design.widget.CollapsingToolbarLayout...> 
</android.support.design.widget.AppBarLayout> 

它的工作原理，並施放在的LinearLayout陰影：

<LinearLayout 
    xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent"> 

    <include layout="@layout/app_bar_large" /> 
</LinearLayout> 

然而，當我把它放到CoordinatorLayout陰影消失：

<android.support.design.widget.CoordinatorLayout 
    xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent"> 

    <include layout="@layout/app_bar_large" /> 
</android.support.design.widget.CoordinatorLayout> 

我該如何讓appbar再次顯示其陰影？

Answer 1

這實際上是CollapsingToolbarLayout一個實現細節，如見於source code：

if (Math.abs(verticalOffset) == scrollRange) { 
    // If we have some pinned children, and we're offset to only show those views, 
    // we want to be elevate 
    ViewCompat.setElevation(layout, layout.getTargetElevation()); 
} else { 
    // Otherwise, we're inline with the content 
    ViewCompat.setElevation(layout, 0f); 
} 

當CollapsingToolbarLayout是顯示非釘扎元素其去除高程 - 缺省值，它只有當只有固定的孩子可見時纔會升高。

Answer 2

的原因是上面，試試這個解決：

appBarLayout.addOnOffsetChangedListener(new AppBarLayout.OnOffsetChangedListener() { 
     @Override 
     public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) { 
      //some other code here 
      ViewCompat.setElevation(appBarLayout, The Elevation In Px); 
     } 
    });