Access resource defined in theme and attrs.xml android

Question

I have a scenario in which I want to set a Drawable depending upon the theme defined.

To explain this further, Here is what I have in code:

\res\values\attrs.xml

<resources>
    <declare-styleable name="AppTheme">
        <attr name="homeIcon" format="reference" />
    </declare-styleable>
</resources>

res\values\styles.xml

<resources>
    <style name="AppTheme" parent="android:style/Theme">
        <item name="attr/homeIcon">@drawable/ic_home</item>
    </style>
</resources>

AndroidManifest.xml

    <application android:label="@string/app_name"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity" android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

So as you have noticed I am defining a custom attr homeIcon and setting the attribute value in AppTheme.

When I define this attribute in a layout XML and try to access it it works smoothly

<ImageView android:id="@+id/img"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:src="?attr/homeIcon" />

and renders the Drawable ic_home in an ImageView.

But I am not able to figure out how to access the Drawable programmatically.

I tried to do this with a work around, by defining a holder LayerList Drawable, which results in resource not found exception:

<?xml version="1.0" encoding="utf-8"?>
<layer-list
    xmlns:android="http://schemas.android.com/apk/res/android" >
    <item
        android:drawable="?attr/homeIcon" />
</layer-list>

Summary I want to access the Drawable defined in a custom defined Theme programmatically.

Answer 1

I think you can get the Drawable with this code:

TypedArray a = getTheme().obtainStyledAttributes(R.style.AppTheme, new int[] {R.attr.homeIcon});     
int attributeResourceId = a.getResourceId(0, 0);
Drawable drawable = getResources().getDrawable(attributeResourceId);
a.recycle();

Answer 2

Another possible way to do it:

  public static int getResIdFromAttribute(final Activity activity,final int attr)
    {
    if(attr==0)
      return 0;
    final TypedValue typedvalueattr=new TypedValue();
    activity.getTheme().resolveAttribute(attr,typedvalueattr,true);
    return typedvalueattr.resourceId;
    }

Or in Kotlin:

@JvmStatic
fun getResIdFromAttribute(activity: Activity, attr: Int): Int {
    if (attr == 0)
        return 0
    val typedValue = TypedValue()
    activity.theme.resolveAttribute(attr, typedValue, true)
    return typedValue.resourceId
}

no need to recycle anything here...

usage:

int drawableResId=getResIdFromAttribute(this,R.attr.homeIcon);
Drawable drawable = getResources().getDrawable(drawableResId);

Answer 3

I used below method to get resource id form style attribute. Then it can be used for drawable, string, dimension so on.

TypedArray typedArray = context.getTheme().obtainStyledAttributes(new int[] { R.attr.attrName });   
int resourceId = typedArray.getResourceId(0, defaultResourceId);
typedArray.recycle();

cheers :-)

Answer 4

If you are using support / design library easier way to get drawables now is -

Context.getDrawable(int)

or

ContextCompat.getDrawable(Context, int)

reference - https://plus.google.com/+BenjaminWeiss/posts/M1dYFaobyBM

Answer 5

Here are the results of my investigation, regarding this topic. If we have declare-stylable then we can override those values in themes.

So far the best way that I found how to get them is the following.

TypedArray a = context.getTheme().obtainStyledAttributes(R.styleable.AppTheme);
a.getDrawable(R.styleable.AppTheme_homeIcon);

By using R.styleable.AppTheme_homeIcon we are referencing exactly that attribute that we want. For example if we would have few more attributes, then we can reference them as follows:

a.getColor(R.styleable.AppTheme_color,defaultValue);
a.getDimension(R.styleable.AppTheme_width,defaultWidth);

And if in current theme those attributes were not defined you will get default values and no Exceptions.