user3420815 user3420815 - 5 months ago 18
Android Question

Using <include> tag with ?attr/myAttr

I'm trying to include different layouts in my View depending on the parent

Theme
.

Following the idea:

attrs.xml

<attr name="themeLayout" format="reference" />


styles.xml

<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
<item name="themeLayout">@layout/layout_a</item>
</style>

<style name="AppThemeSecond" parent="Theme.AppCompat.Light.DarkActionBar">
<item name="themeLayout">@layout/layout_b</item>
</style>


activity.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<include layout="?attr/themeLayout" />

</RelativeLayout>


When I run the Code above I'll get the following Exception:

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.my.package/com.my.package.MainActivity}: android.view.InflateException: You must specifiy a valid layout reference. The layout ID ?attr/themeLayout is not valid.
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: android.view.InflateException: You must specifiy a valid layout reference. The layout ID ?attr/themeLayout is not valid.
at android.view.LayoutInflater.parseInclude(LayoutInflater.java:866)


What am I doing wrong? Is it possible to do this at all?

Note #1: I set the
Theme
of my
MainActivity
to
android:theme="@style/AppTheme"


Note #2: In the Design-View of the Layout Editor everything works as expected. If I switch the Theme, the include gets updated properly.

See the following Screenshots as well:

preview design tab android studio

Answer

Unfortunately this is not possible but I really like the idea. I have tracked the flow of LayoutInflater and it requieres the layout attribute to be TypedValue.TYPE_REFERENCE which means ?attr is not allowed. They even left a comment in the method to explain.

public int getAttributeResourceValue(int idx, int defaultValue) {
    int t = nativeGetAttributeDataType(mParseState, idx);
    // Note: don't attempt to convert any other types, because
    // we want to count on aapt doing the conversion for us.
    if (t == TypedValue.TYPE_REFERENCE) {
        return nativeGetAttributeData(mParseState, idx);
    }
    return defaultValue;
}

android.content.res.XmlBlock.java:385

Basically you have done nothing wrong -- the inflation in Preview works differently which caused the confusion.

Comments