android: how do I check if dialogfragment is showing

问题

I launch my dialog fragment using

FragmentTransaction ft = 
getFragmentManager().beginTransaction();
MyDialogFragment dialog = new MyDialogFragment()
dialog.show(ft, "dialog");

then to get a handle on it I do

Fragment prev = getFragmentManager().findFragmentByTag("dialog");

but once I get prev, how do I check if it is showing?

Back Story

My problem is that my looping code keeps launching the dialog again and again. But if the dialog is already showing, I don't want it to launch again. This back story is just for context. The answer I seek is not: "move it out of the loop."

回答1:

simply check if it's null

if(prev == null)
    //There is no active fragment with tag "dialog"
else
    //There is an active fragment with tag "dialog" and "prev" variable holds a reference to it.

Alternatively, you could check the activity the fragment prev is currently associated with, however, make sure you ask that after you make sure it's not null or you'll get a NullPointerException. Like this:

if(prev == null)
    //There is no active fragment with tag "dialog"
else
    if(prev.getActivity() != this) //additional check
        //There is a fragment with tag "dialog", but it is not active (shown) which means it was found on device's back stack.
    else
        //There is an active fragment with tag "dialog"

回答2:

 if (dialogFragment != null
     && dialogFragment.getDialog() != null
     && dialogFragment.getDialog().isShowing()
     && !dialogFragment.isRemoving()) {
            //dialog is showing so do something 
 } else {
     //dialog is not showing
 }

回答3:

I added this to be inside my custom dialog fragment, so I don't have to worry about any logic on the outside. Override the show() and onDismiss() methods, with a boolean shown field:

  private static boolean shown = false;

    @Override
    public void show(FragmentManager manager, String tag) {
        if (shown) return;

        super.show(manager, tag);
        shown = true;
    }

    @Override
    public void onDismiss(DialogInterface dialog) {
        shown = false;
        super.onDismiss(dialog);
    }

If you want to check whether it is shown or not, you can create a getter for the shown boolean.

来源：https://stackoverflow.com/questions/21352571/android-how-do-i-check-if-dialogfragment-is-showing