java – Refreshing a view inside a fragment-ThrowExceptions

Exception or error:

I have searched the numerous questions that look like this one, but haven’t found my answer in any of them.

I have an activity that has 3 tabs accessible through the action bar. I achieved this by adding 3 fragments that inflate a custom view I made extending the view class.

At the moment the database changes, I try to refresh the view in my tab by calling invalidate()/postinvalidate(), but this does not work. The same is true for calling onCreateView of the fragment just as many other options I considered.

When I go to another tab and go back, however, the change has been made and my view is updated as it should be.

How can I simulate the same thing that happens when changing to another tab? What does happen. I tried to look at the Fragment lifecycle (tried to call onCreateView()) to figure it out but it just doesn’t want to refresh/redraw as it should.

The data is loaded properly, as the data is changed when I change to another tab.

I deleted some of the code as it is no longer relevant. I implemented Cursorloaders instead of my own Observer pattern to notify a change. This is my main activity right now.

The question is what should I do now if I want to redraw the view inside these fragments. If I apply fragmentObject.getView().invalidate() it does not work. I’m having the same problem as before, but now my Observer to notify a change in the database is properly implemented with loaders.

public class ArchitectureActivity extends Activity implements LoaderManager.LoaderCallbacks<Cursor> {

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);     
    setContentView(R.layout.main);

    ActionBar actionbar = getActionBar();
    actionbar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    ActionBar.Tab EditTab = actionbar.newTab().setText("Edit");
    ActionBar.Tab VisualizeTab = actionbar.newTab().setText("Visualize");
    ActionBar.Tab AnalyseTab = actionbar.newTab().setText("Analyse");

    Fragment editFragment = new EditFragment();
    Fragment visualizeFragment = new VisualizeFragment();
    Fragment analyseFragment = new AnalyseFragment();

    EditTab.setTabListener(new MyTabsListener(editFragment));
    VisualizeTab.setTabListener(new MyTabsListener(visualizeFragment));
    AnalyseTab.setTabListener(new MyTabsListener(analyseFragment));

    actionbar.addTab(EditTab);
    actionbar.addTab(VisualizeTab);
    actionbar.addTab(AnalyseTab);

    ArchitectureApplication architectureApplication = (ArchitectureApplication)getApplicationContext();
    architectureApplication.initialize();

    getLoaderManager().initLoader(0, null, this);
    getLoaderManager().initLoader(1, null, this);
}

public Loader<Cursor> onCreateLoader(int id, Bundle args) {
    if (id == 0){
        return new CursorLoader(this, GraphProvider.NODE_URI , null, null, null, null);
    } else if (id == 1){
        return new CursorLoader(this, GraphProvider.ARC_URI , null, null, null, null);
    }
    return null;
}

public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) {
    // Reloading of data, actually happens because when switching to another tab the new data shows up fine
    Log.e("Data", "loaded");
}

public void onLoaderReset(Loader<Cursor> loader) {
}
}
How to solve:
  1. Don’t try to call onCreateView() yourself… it’s a lifecycle method and should be called only by the framework.

  2. Fragments are re-usable UI components. They have their own lifecycle, display their own view, and define their own behavior. You usually don’t need to have your Activity mess around with the internal workings of a Fragment, as the Fragment‘s behavior should be self-contained and independent of any particular Activity.

    That said, I think the best solution is to have each of your Fragments implement the LoaderManager.LoaderCallbacks<D> interface. Each Fragment will initialize a Loader (i.e. a CursorLoader if you are using a ContentProvider backed by an SQLite database), and that Loader will be in charge of (1) loading the data on a background thread, and (2) listening for content changes that are made to the data source, and delivering new data to onLoadFinished() whenever a content change occurs.

    This solution is better than your current solution because it is entirely event-driven. You only need to refresh the view when data is delivered to onLoadFinished() (as opposed to having to manually check to see if the data source has been changed each time you click on a new tab).

  3. If you are lazy and just want a quick solution, you might be able to get away with refreshing the view in your Fragment‘s onResume() method too.

###

I had a similar (although not identical) problem that I could solve in the following way:

In the fragment I added

public void invalidate() {
    myView.post(new Runnable() {
        @Override
        public void run() {
            myView.invalidate();
        }
    });
}

and I called this method from the activity when I wanted to refresh the view myView of the fragment. The use of post() ensures that the view is only invalidated when it is ready to be drawn.

###

I’ve found a workaround to refresh the view inside my fragment. I recreated (new CustomView) the view every time the database has been updated. After that I call setContentView(CustomView view). It looks more like a hack, but it works and nothing else that I tried does.

Although my problem was not actually solved, I gave the reward to Alex Lockwood. His advice on Loaders made my application better and it caused me to keep looking for a solution that I eventually found.

###

I had the same issue.
My solution was detach fragment and attach it again.

        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        Fragment f = getFragment(action);
        if(forceUpdate)
        {
            fragmentTransaction.detach(f);
            fragmentTransaction.attach(f);
        }
        fragmentTransaction.replace(R.id.mainFragment, f);
        fragmentTransaction.commit();
        currentAction = action;

###

The fastest solution working for me:

 @Override
    public void onPause() {
        super.onPause();
        if (isRemoving() && fragmentView != null) {
            ((ViewGroup) fragmentView).removeAllViews();
        }
    }

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