我可以在Android中将FloatingActionButton投射到ImageButton吗？

Question

My app has a floating-action-button, but it needs to support KitKat (API 19). For the floating-action-button, I use an ImageButton by default and swap it (in the layout) for the real FloatingActionButton for API 21 or higher.

In my activity, I have the code to get the fab as this...

ImageButton mAddProject;

...

mAddProject = (ImageButton) findViewById(R.id.new_project_fab);

Of course, this works fine in Android 20 or lower, but when being run in Android 21 or higher, it throws an error

Caused by: java.lang.ClassCastException: android.support.design.widget.FloatingActionButton cannot be cast to android.widget.ImageButton

The doc says that FloatingActionButton is extended from ImageButton . I imagine this would allow me to cast it to ImageButton . I guess I'm wrong and don't understand how casting works.

Is it possible to cast FloatingActionButton to ImageButton ?

Answer 1

Explanation

The casting is actually working. It just is that the button does not exist yet. I think that the following code should work:

FloatingActionButton mAddProject = (FloatingActionButton) findViewById(R.id.new_project_fab);
ImageButton mAddProjectImageButton = (ImageButton) mAddProject

Since this code won't run below API 19, I suggest the following:

Suggestion

I would suggest that you add the button programmatically. You should check the version and whenever it is API21+, you add the FAB. Whenever it is 20-, you add the ImageButton. This way you are sure that you have the correct button working for the correct API.

Example:

int currentapiVersion = android.os.Build.VERSION.SDK_INT;
if (currentapiVersion >= android.os.Build.VERSION_CODES.LOLLIPOP){
    // Add the FAB button
} else{
    // Add the ImageButton
}