Android 5.0 - ProgressBar cannot be displayed over a Button

问题

I think the title is pretty explicit about my problem... So here is my layout :

            <RelativeLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content">

                <Button
                    android:id="@+id/button_action"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:text="Login" />

                <ProgressBar
                    android:id="@+id/progress_bar"
                    android:layout_width="50dp"
                    android:layout_height="50dp"
                    android:layout_centerInParent="true"/>

            </RelativeLayout>

On android SDKs < 21, no problem, the ProgressBar is correctly displayed over the Button and centered in the Button. But on Android 5.0, the ProgressBar is displayed behind the Button.

So you can see it's correctly positionned it when you activate the option "Show layout bounds" in Developer Options settings, but you can't see anything on the screen without that option.

Would anybody know how to fix this? I guess it's a matter of elevation recently introduced, but I really don't know how to take care of it. For the record, I'm using the recently released Theme.AppCompat style from the support.v7.

EDIT:

I also tried to apply setElevation(0) and setTranslationY(0) to the Button programmatically but it didn't change anything. So I wonder if it has to deal with the elevation.

Thanks in advance guys

Mathieu

回答1:

You can use android:translationZ attribute in ProgressBar:

        <ProgressBar
            android:id="@+id/progress_bar"
            android:layout_width="50dp"
            android:layout_height="50dp"
            android:translationZ="2dp"
            android:layout_centerInParent="true"/>

回答2:

Same issue here, my simple "hack" was too wrap the Button into another FrameLayout. This way I don't care about the api version and other elevation issue ;)

<FrameLayout
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center" >

        <FrameLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content">
                <Button
                    android:id="@+id/button_action"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:text="Login" />
        </FrameLayout>

        <ProgressBar
            android:id="@+id/progress_bar"
            android:layout_width="50dp"
            android:layout_height="50dp" />
</FrameLayout>

回答3:

Same question being asked here, with a better explanation of the issue:

https://stackoverflow.com/a/27216368/235910

To quote @CommonsWare:

The problem appears Android 5.0's elevation property. Apparently, the RelativeLayout Z-axis ordering is tied into elevation. If both widgets have the same elevation, the RelativeLayout will determine the Z-axis order -- you can see that if you were to switch your layout to be both Button widgets, for example. However, if one widget (Button) has an elevation, and another widget (ImageView) does not, the elevation will take precedence.

You can remove the Button elevation via android:stateListAnimator="@null" or by defining your own custom animator. Or, you can add some elevation to your ImageView to get it to be higher on the Z axis than is the Button.

回答4:

It is better to set android:translationZ more than 2dp. Your view/widget will disappear when you press the button. I explained the reason here.

<!-- Elevation when button is pressed -->
<dimen name="button_elevation_material">1dp</dimen>
<!-- Z translation to apply when button is pressed -->
<dimen name="button_pressed_z_material">2dp</dimen>

Button have these two values and defined in the framework.

回答5:

If you add 'androidx.core:core' to your build.gradle, you can use this code for API < 21:

ViewCompat.setTranslationZ(viewToElevate, 5);

回答6:

Probably the simplest way is to use the FrameLayout since it was created to make layouts whose child views are ordered by z-index:

    <FrameLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center" >

            <Button
                android:id="@+id/button_action"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="Login" />

            <ProgressBar
                android:id="@+id/progress_bar"
                android:layout_width="50dp"
                android:layout_height="50dp" />
    </FrameLayout>

I'm not sure what does your layout look like, so maybe you'll need to play with android:layout_gravity.

来源：https://stackoverflow.com/questions/26524552/android-5-0-progressbar-cannot-be-displayed-over-a-button