不幸的是，如果我将PaintDrawable强制转换为Drawable，则在调试时应用程序已停止

Question

I'm studying and trying to make some Android application with android studio. But I found something that I can't understand.

If I write the sentence below, there is no problem:

TextView vm = new TextView(this);

Drawable pnt = vm.getBackground();

but, if I write a sentence like below, where I cast PaintDrawable to the righthand, and build this app and install apk to my device, app doesn't work showing message "Unfortunately, the app has stopped".

TextView vm = new TextView(this);

PaintDrawable pnt = (PaintDrawable) vm.getBackground();

Answer 1

TextView::getBackground returns a Drawable , not necessarily a PaintDrawable.

You are attempting to downcast to PaintDrawable without checking whether you can do so. Try this:

TextView vm = new TextView(this);

if (vm.getBackground() instanceof PainDrawable) {
    PaintDrawable pnt = (PaintDrawable) vm.getBackground();
    // ...
}
else {
    Log.d("SomeTag", vm.getBackground().getClass());
}