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Attribute Adapters

Attribute adapters handle attributes for a specific view.

Implementing an Adapter

Basic

To implment an adapter, you'll have to write a class extending one of the existing adapters.

Adapters extend other adapters in the same way as Android's view classes extend other views. For example, android.widget.CompoundButton extends android.widget.Button, in the same way com.itsaky.layoutinflater.adapters.android.widget.CompoundButtonAttrAdapter extends com.itsaky.layoutinflater.adapters.android.widget.ButtonAttrAdapter. In this way, we don't have to rewrite whole logic again to implement adapters for every other widget.

Naming an adapter

If you look at the package name and the simple name of the adapter classes mentioned above, you'll find that there is a specific way an adapter is named.

An adpater should be named in the following way : com.itsaky.layoutinflater.adapters.<package_name>.<simple_name>AttrAdapter, where, <package_name> is the package name of the widget you are implementing an adapter for and <simple_name> is the simple name of the widget. The simple name is then suffixed with AttrAdapter.

Here is an example : Assume we have to implement an adapter for android.widget.Button. Here, <package_name> is android.widget and <simple_name> is Button.

So, the adapter implentation class should be com.itsaky.layoutinflater.adapters.android.widget.ButtonAttrAdapter.

Why such naming?

We use reflection to automatically create an adapter when inflating a view. For example, if android.widget.Button instance is being created, we could simply create an adapter instance using reflection by getting the package name and simple name of the widget.

See XMLLayoutInflater#onCreateAttributeAdapter(View).

Precautions

  • Make sure you correctly spell the file names. As you might already know, file names are case sensitive.
  • Some methods (or even classes) are not available for earlier versions of Android. The classes or methods you're using must be compatible with API 24.

You could also check if you can use a method. Some methods are already implemented in ViewAttrAdapter so you won't have to rewrite them. For example:

isApi26() // Android 8 (Oreo)
isApi28() // Android 9 (Pie)
isApi29() // Android 10 (Q)
isApi30() // Android 11 (R)