[SOLVED] Android: <declare-styleable> method attributes

Android: <declare-styleable> method attributes

How does one accept methods as values, in attributes? Like in the onClick attribute for a View:

<Button android:onClick="onClickMethod"/>

How to define custom attributes that accept methods?

I know we use <declare-styleable> in resources, but how do we make it accept methods?

Solution

Android uses reflection to find the name of the method and invoke it. You can see an example in the source starting at line 4209 https://github.com/android/platform_frameworks_base/blob/master/core%2Fjava%2Fandroid%2Fview%2FView.java#L4209

             case R.styleable.View_onClick:
                if (context.isRestricted()) {
                    throw new IllegalStateException("The android:onClick attribute cannot "
                            + "be used within a restricted context");
                }

                final String handlerName = a.getString(attr);
                if (handlerName != null) {
                    setOnClickListener(new DeclaredOnClickListener(this, handlerName));
                }
                break;

If the method name isn't null, it creates a new DeclareOnClickListener() class and initializes it with the method name.

The DeclareOnClickListener() class is defined at line 4435 https://github.com/android/platform_frameworks_base/blob/master/core%2Fjava%2Fandroid%2Fview%2FView.java#L4435