Android: replacing text in activity after click event on fragment button

Question

I got lots of NPEs and was wondering how you manage this common task.

There is a button in my fragment, here the WelcomeFragment.
The button will clicked and the event is handled in the MainActivity class.
The fragment is a NPE, the view, too ...

Here is my code snippet of my MainActivity:

@Override
public void onClick(View v) { 
    switch (v.getId()) {
        case R.id.button1:
            ...
            WelcomeFragment welcomeFragment = (WelcomeFragment) getFragmentManager().findFragmentByTag(WelcomeFragment.WELCOME_FRAGMENT_TAG);
            if (welcomeFragment == null){
                welcomeFragment = new WelcomeFragment();
            }
            View view = welcomeFragment.getView();
            if (view == null){
                view = new View(this);
            }
            TextView text1 = (TextView) view.findViewById(R.id.welcomeFragmentHeader);
            text1.setText(newTextToShow + resStr);
            break;

...

where is the NPE fired from? some more details? .. – Pier Giorgio Misley Dec 27 '16 at 15:10 — Pier Giorgio Misley, Dec 27 '16 at 15:10

score 0 · Answer 1 · edited May 23 '17 at 12:16

I'm assuming your app crashes with an NPE the first time you click this button, when there is no WelcomeFragment instance:

(WelcomeFragment) getFragmentManager().findFragmentByTag(WelcomeFragment.WELCOME_FRAGMENT_TAG);

returns null, so you enter the if statement and construct a WelcomeFragment.

This is not the right way to make a fragment. It's contents are not inflated this way, thus it has no views in it. Therefore, your later call to (TextView) view.findViewById(R.id.welcomeFragmentHeader); also returns null. Therefore you are calling setText() on a null object in the next line, and getting an NPE.

You need to properly inflate add your fragment to your activity as outline in here, or change your app logic.

Android: replacing text in activity after click event on fragment button

1 Answers1