Unexpected cast to AppCompatButton: layout tag was Button

问题

From AppCompatButton reference page:

This will automatically be used when you use Button in your layouts. You should only need to manually use this class when writing custom views.

I'm casting a normal Button to AppCompatButton, so that I can use setSupportBackgroundTintList method:

AppCompatButton button = (AppCompatButton) findViewById(R.id.normalButton);
button.setSupportBackgroundTintList(ColorStateList.valueOf(tintColor));

It builds and runs without any problem, but Android Studio 1.4 gives me the annoying red highlight on casting line:

Unexpected cast to AppCompatButton: layout tag was Button

Any ideas?

回答1:

It looks like a bug in the IDE type checking - Button is direct ancestor of AppCompatButton, so casting to AppCompatButton should be okay. I believe you can safely call it like this:

Button button = (Button) findViewById(R.id.normalButton);
((AppCompatButton)button).setSupportBackgroundTintList(ColorStateList.valueOf(tintColor));

or better

((TintableBackgroundView)button).setSupportBackgroundTintList(ColorStateList.valueOf(tintColor));

If you use Butterknife, everything works as expected without any warning:

@Bind(R.id.normalButton)
AppCompatButton button;

来源：https://stackoverflow.com/questions/33495164/unexpected-cast-to-appcompatbutton-layout-tag-was-button