Prevent DialogFragment from dismissing when button is clicked

Override the default button handlers in OnStart() to do this.

@Override
public Dialog onCreateDialog(Bundle savedInstanceState)
{
    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
    builder.setMessage("Test for preventing dialog close");
    builder.setPositiveButton("Test", 
        new DialogInterface.OnClickListener()
        {
            @Override
            public void onClick(DialogInterface dialog, int which)
            {
                //Do nothing here because we override this button later to change the close behaviour. 
                //However, we still need this because on older versions of Android unless we 
                //pass a handler the button doesn't get instantiated
            }
        });
    return builder.create();
}

@Override
public void onStart()
{
    super.onStart();    //super.onStart() is where dialog.show() is actually called on the underlying dialog, so we have to do it after this point
    AlertDialog d = (AlertDialog)getDialog();
    if(d != null)
    {
        Button positiveButton = (Button) d.getButton(Dialog.BUTTON_POSITIVE);
        positiveButton.setOnClickListener(new View.OnClickListener()
                {
                    @Override
                    public void onClick(View v)
                    {
                        Boolean wantToCloseDialog = false;
                        //Do stuff, possibly set wantToCloseDialog to true then...
                        if(wantToCloseDialog)
                            dismiss();
                        //else dialog stays open. Make sure you have an obvious way to close the dialog especially if you set cancellable to false.
                    }
                });
    }
}

See my answer here https://stackoverflow.com/a/15619098/579234 for more explanation and examples on other dialog types too.