monodroid/xamarin custom attributes are empty using ObtainStyledAttributes

Question

Trying to pass a custom attribute from a parent layout to a child layout.

The TypedArray returned from ObtainStyledAttributes() doesn't seem to have the corresponding custom values for the custom properties I've created, although I can map their IDs to the values in Resource.designer.

---

Attr.xml:

<resources>
<declare-styleable name="HeaderView">
    <attr name="bgcolor" format="color" />
    <attr name="testing" format="string" />
</declare-styleable>

Main.xaml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:custom="http://schemas.android.com/apk/res">
    <LinearLayout
        android:orientation="vertical"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent">
        <views.HeaderView
            android:id="@+id/hdrWatchList"
            android:layout_width="fill_parent"
            android:layout_height="20.0dp"
            custom:bgcolor="@color/blue"
            custom:testing="testing text buddy" />

View Class:

    public HeaderView (Context context, IAttributeSet attrs) :
        base (context, attrs)
    {
        int[] styleAttrs = Resource.Styleable.HeaderView;
        TypedArray a = context.ObtainStyledAttributes(attrs, styleAttrs);

        string  sid = a.GetString(Resource.Styleable.HeaderView_testing);
        int  id = a.GetColor(Resource.Styleable.HeaderView_bgcolor, 555);

        Log.Info( "testing", "resource sid : " + sid); // RETURNS ''
        Log.Info( "testing", "resource id : " + id); // RETURNS DEF 555

Answer 1

I think the issue lies with how you specified your xmlns:custom namespace. You need to add your applications namespace at the end of the string your already have like so:

xmlns:custom="http://schemas.android.com/apk/res/my.awesome.namespace"

You also need to have a AndroidManifest.xml defined for your Android project, where you have defined the same namespace.

Also the lines:

int[] styleAttrs = Resource.Styleable.HeaderView;
TypedArray a = context.ObtainStyledAttributes(attrs, styleAttrs);

Look a bit strange to me and I would just write:

var a = context.ObtainStyledAttributes(attrs, Resource.Styleable.HeaderView);

Especially if you are not using styleAttrs later on.

EDIT: since Android SDK rev 17 it is possible to use:

xmlns:custom="http://schemas.android.com/apk/res-auto"

instead of having to write the entire namespace.