Overlapping Views in Android

问题

Is it possible to have overlapping views in Android? I would like to have an ImageView with a transparent png in the front and another view in the background.

edit:

This is what I have at the moment, the problem is that the image in the imageView is not transparent, the parts that should be transparent are just black.

<RelativeLayout xmlns:android=\"http://schemas.android.com/apk/res/android\" 
    android:orientation=\"vertical\"
    android:layout_width=\"wrap_content\"
    android:layout_height=\"wrap_content\"
    android:id=\"@+id/gallerylayout\"
>
<Gallery android:id=\"@+id/overview\"
    android:layout_width=\"fill_parent\"
    android:layout_height=\"wrap_content\"
    />

 <ImageView android:id=\"@+id/navigmaske\"
    android:layout_width=\"fill_parent\"
    android:layout_height=\"wrap_content\"
    android:src=\"@drawable/navigmask\"
    /> 

</RelativeLayout>

edit:

I got it to work, it was a theme file from another programmer on the team. Just changed this

<item name=\"android:background\">#FF000000</item>

to this

<item name=\"android:background\">#00000000</item>

回答1:

Android handles transparency across views and drawables (including PNG images) natively, so the scenario you describe (a partially transparent ImageView in front of a Gallery) is certainly possible.

If you're having problems it may be related to either the layout or your image. I've replicated the layout you describe and successfully achieved the effect you're after. Here's the exact layout I used.

<RelativeLayout 
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:id="@+id/gallerylayout"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent">
  <Gallery
    android:id="@+id/overview"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content"
  />
  <ImageView
    android:id="@+id/navigmaske"
    android:background="#0000"      
    android:src="@drawable/navigmask"
    android:scaleType="fitXY"
    android:layout_alignTop="@id/overview"
    android:layout_alignBottom="@id/overview"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content"
  />
</RelativeLayout>

Note that I've changed the parent RelativeLayout to a height and width of fill_parent as is generally what you want for a main Activity. Then I've aligned the top and bottom of the ImageView to the top and bottom of the Gallery to ensure it's centered in front of it.

I've also explicitly set the background of the ImageView to be transparent.

As for the image drawable itself, if you put the PNG file somewhere for me to look at I can use it in my project and see if it's responsible.

回答2:

Also, take a look at FrameLayout, that's how the Camera's Gallery application implements the Zoom buttons overlay.

回答3:

If you want to add you custom Overlay screen on Layout, you can create a Custom Linear Layout and get control of drawing and key events. You can my tutorial- Overlay on Android Layout- http://prasanta-paul.blogspot.com/2010/08/overlay-on-android-layout.html

回答4:

Visible gallery changes visibility which is how you get the gallery over other view overlap. the Home sample app has some good examples of this technique.

回答5:

The simples way arround is to put -40dp margin at the buttom of the top imageview

回答6:

Yes, that is possible. The challenge, however, is to do their layout properly. The easiest way to do it would be to have an AbsoluteLayout and then put the two images where you want them to be. You don't need to do anything special for the transparent png except having it added later to the layout.

来源：https://stackoverflow.com/questions/961944/overlapping-views-in-android