移除 AppBarLayout 小部件下面的阴影

Simply use app:elevation="0dp" inside "AppBarLayout" to remove the shadow. It has always worked for me. Hope it works for you.

I tried app:elevation="0dp" but the toolbar desappear, but using app:elevation="0.1dp" made the trick.

Hope this helps somebody else.

this problem only occurs when api version >= 21, try below codes:

appBar.setOutlineProvider(null);

remember to check api version

EDIT :

Below is the source code of setOutlineProvider.

   /**
* Sets the {@link ViewOutlineProvider} of the view, which generates the Outline that defines
* the shape of the shadow it casts, and enables outline clipping.
* <p>
* The default ViewOutlineProvider, {@link ViewOutlineProvider#BACKGROUND}, queries the Outline
* from the View's background drawable, via {@link Drawable#getOutline(Outline)}. Changing the
* outline provider with this method allows this behavior to be overridden.
* <p>
* If the ViewOutlineProvider is null, if querying it for an outline returns false,
* or if the produced Outline is {@link Outline#isEmpty()}, shadows will not be cast.
* <p>
* Only outlines that return true from {@link Outline#canClip()} may be used for clipping.
*
* @see #setClipToOutline(boolean)
* @see #getClipToOutline()
* @see #getOutlineProvider()
*/
public void setOutlineProvider(ViewOutlineProvider provider) {
mOutlineProvider = provider;
invalidateOutline();
}

It is said that If the ViewOutlineProvider is null, if querying it for an outline returns false, or if the produced Outline is {@link Outline#isEmpty()}, shadows will not be cast.

So, if you want to remove shadow, you'd better use this method instead of setting app:elevation. It seems like that changing the elevation to remove shadow is a kind of side effect. And changing the elevation may cause some other problems in some cases.

This is the way that I came up with app:elevation="0dp" to remove the shadow.Perfectly works.

With latest appcompat versions, the trick setting app:elevation="0.1dp" in xml doesn't work any more.

So far I have found two solutions.

1. Instead of setting app:elevation, try to use a stateListAnimator. For example, in code:

   if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
   StateListAnimator stateListAnimator = new StateListAnimator();
   stateListAnimator.addState(new int[0], ObjectAnimator.ofFloat(appBarLayout, "elevation", 0.1f));
   appBarLayout.setStateListAnimator(stateListAnimator);
   }
   

2. An easier way is you still set app:elevation="0dp" in xml as normal, but in code:

   appBarLayout.bringToFront();
   

Credit goes to these two discussions:

ToolBar disappears when setting elevation for AppBarLayout

when set app:elevation="0dp" then hamburgermenu not showing to toolbar

Add app:elevation="0dp" on your AppBarLayout. like this example

<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:elevation="0dp"
android:theme="@style/AppTheme.AppBarOverlay">


<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/AppTheme.PopupOverlay" />


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

Programmatically you can use this : getSupportActionBar().setElevation(0.0f);

For all those who do not want to use bringToFront() and elevation="0dp" makes the toolbar disappear:

app:elevation="0dp" combinded with android:translationZ="0.1dp" worked for me.

<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay"
app:elevation="0dp"
android:translationZ="0.1dp"
>


<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="@null"
app:popupTheme="@style/AppTheme.PopupOverlay"/>


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

Use android:stateListAnimator="@null". No side effect.

<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:animateLayoutChanges="true"
android:stateListAnimator="@null"
>

I am doing this on Kotlin minSdkVersion 21 with AppBarLayout & TabLayout so: app:elevation="0dp" does indeed help me solve the shadow problem BUT using this solution make it so that I will not be able to press the button on the TabLayout.

so combine app:elevation="0.1dp" & app:elevation="0dp"i can fix the shadow and still be able to interact with my tab layout.