为什么 Android drawable 不显示为列表项背景？

Question

I cannot figure out why the drawable I'm using is not showing up as the background, with border, for list items. Here is the drawable in a file named ticketborder.xml:

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <solid android:color="#ff00ff00"/>
    <stroke android:width="4dp" android:color="#ffff0000"/>
</shape>

In the designer, I see a rendering of this. It looks correct. I also use this as the background in the XML for the layout for the items and it looks good there.

In the getView() function in the adapter, I tried to get around any XML issues and have this line:

v.setBackground( ContextCompat.getDrawable(context, R.drawable.ticketborder ) );

This does nothing and the border doesn't show up and neither does the background color. To test that the code can even set the background of this view, I did this:

v.setBackgroundColor( Color.RED );

This works just fine. Somehow, it is only the drawable that won't work. Or maybe it's something to do with this being a list item that gets used when the getView() function is calledin the adapter. I know the drawable is valid because the designer shows it. The designer also shows a preview of the border and background in the layout for the list items. Here is the layout for the list item that uses the drawable:

?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.LinearLayoutCompat
    android:orientation="vertical"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="wrap_content"
    android:layout_width="match_parent"
    android:focusable="false"
    android:focusableInTouchMode="false"
    android:clickable="false"
    android:padding="44dp"
    android:descendantFocusability="blocksDescendants"
    android:background="@drawable/ticketborder">
    ...

One more thing I should mention is that when I wrote the code for this a few months ago, the borders were showing up fine. The only thing that happened that I can recall is an update to Android Studio. I'm sure I screwed up some code in the past few months but I can't for the life of me figure out how I could do anything that would make the background drawable not work right while a simple color works just fine.

Here is a shot of the designer when I'm working on the drawable:

Here is a picture of the design view when I am editing the layout of the list item:

And finally, a picture of the screen on the simulator (a physical phone has the same behavior) when using the red background color:

and using the drawable:

EDIT:

This worked but I don't know why and I am not sure how to modify the color and border color in code:

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle">
            <solid android:color="#00ff00"/>
            <stroke android:width="2dp" android:color="#ff0000"/>
        </shape>
    </item>
</layer-list>

I have no explanation as to why this is working and the previous shape definition did not work. I am fairly certain that I have other LinearLayout elements that have shapes because I have a few places where I add rounded corners on borders around UI elements. I'll need to check to see if those stopped working :(

Answer 1

I fixed it by adding a layer to the XML for the background and border shape:

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle">
            <solid android:color="#00ff00"/>
            <stroke android:width="2dp" android:color="#ff0000"/>
        </shape>
    </item>
</layer-list>

I am not at all happy with this since I need to get the background of the element in code and alter the colors to fit with what a server is delivering to this client app. I also still want an explanation about why this works.

Note that I did try something like this initially so I'm also not sure how I got it wrong the first time I tried it. But this does work.