What does ActionBar#setDefaultDisplayHomeAsUpEnabled in Android Support library?

问题

I know what setDisplayHomeAsUpEnabled does, but what is setDefaultDisplayHomeAsUpEnabled for I can only wonder. No documentation found, cannot find anything except it is being used.

回答1:

This method is only available in the Support Action Bar, not in the "native" ActionBar class available since Android 3. More importantly, it is annotated with @hide in the source, meaning it is not part of the official API for third-party developers. That is why it is nowhere documented by Google. You should just not use it.

Having a deeper look into the sources, I found the method implemented in WindowDecorActionBar:

public void setDefaultDisplayHomeAsUpEnabled(boolean enable) {
    if (!mDisplayHomeAsUpSet) {
        setDisplayHomeAsUpEnabled(enable);
    }
}

So basically it does exactly the same as using setDisplayHomeAsUpEnabled, but only if the value has not yet been set manually using the said function.

tldr: you should always use setDisplayHomeAsUpEnabled and ignore the default method.

来源：https://stackoverflow.com/questions/36398448/what-does-actionbarsetdefaultdisplayhomeasupenabled-in-android-support-library