Android: ListView not loading items after orientation change

Question

EDIT - Please read first!

It turns out that I was making a very stupid mistake. My layout contains a WebView that has the exact same background color as the ListView. The WebView is hidden at some point after the activity loads, but I forgot to hide it after an orientation change, so it covered the ListView and it made it seem like it was empty, when in fact it had been loaded correctly. I'll leave this question here as it provides a working example on how to restore ListView data after an orientation change :)

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Well, this seemed pretty easy at the time. I'm trying to restore the data on a ListView after an orientation change. The data is fetched from a web service, so at first I was simply calling the web service after the change took place. This was working fine, but re-fetching the data is way too slow for so simple a situation, so I thought that I would rather save the ListView's state and then just restore it without having to go back to the server.

I'm doing this with onSaveInstanceState:

protected void onSaveInstanceState (Bundle outState) {
    ListAdapter adapter = this.listView.getAdapter();

    if (adapter != null) {
        try {
            String dataSource = ((JSONArrayAdapter)adapter).getDataSource().toString(1);
            outState.putString("dataSource", dataSource);
        } catch (Exception e) {
            Log.w("MainActivity", "Invalid data adapter", e);
        }
    }
}

JSONArrayAdapter is a custom adapter that I'm using, which works with JSONArray objects as its data source. I know that it works since it displays everything correctly before the orientation change.

After saving the ListView data as a JSON string, I try to restore it with onCreate:

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    listView = (ListView)findViewById(R.id.listView);
    progressBar = (ProgressBar)findViewById(R.id.progressBar);

    String dataSource = null;
    if (savedInstanceState != null) {
        dataSource = savedInstanceState.getString("dataSource");
    }

    if (dataSource == null) {
        reloadList(); //this is a call to the web service
    } else {
        try {
            JSONArray array = new JSONArray(dataSource);

            this.listView.setAdapter(new JSONArrayAdapter(getApplicationContext(), array));
            this.progressBar.setVisibility(View.GONE);
        } catch (JSONException e) {
            Log.w("MainActivity", "Invalid data adapter", e);
            reloadList();
        }
    }
}

The result is that I flip the device and there are no errors, but the ListView is empty (or its items are invisible at least). Using the debugger, I've verified that the JSON string is stored correctly. I've even stepped through the getView method on the adapter to make sure that the views are generated correctly. It is also worth noting that the code is not entering any of the catch blocks. Does anyone know what could be causing the ListView to be empty? Thanks

On changing orientation, the activity is destroyed and recreated again. Is onCreate() gets called when you change orientation? — Nitish, Mar 25 '13 at 18:34
Yes, I'm taking that into consideration, I'm trying to recreate the activity's state by setting a new list adapter with the previously loaded data. — JayPea, Mar 25 '13 at 18:36
What is `toString(1)` ? Also what `dataSource` prints after `dataSource = savedInstanceState.getString("dataSource");` (also you are using 2 if while you only need one and this can lead to bugs) — Mr_and_Mrs_D, Mar 25 '13 at 19:00
The 1 just specifies how many spaces to use for indentation on the resulting JSON string. After the line you mention, dataSource contains the proper JSON string, I've checked it in the debugger. — JayPea, Mar 25 '13 at 21:17

score -1 · Answer 1 · edited May 23 '17 at 11:50

-1

Declare android:configChanges in your application's manifest file and in onConfigurationChanged do what you want to do on changing screen orientation.

You can find more detailed discussion here.

edited May 23 '17 at 11:50

Community

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1

answered Mar 25 '13 at 19:06

Nitish

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Thanks, unfortunately, I do want the activity to be destroyed when orientation changes because later on I will switch to a different layout. – JayPea Mar 25 '13 at 21:15

score -1 · Answer 2 · answered Mar 25 '13 at 19:09

-1

Maybe :

protected void onSaveInstanceState (Bundle outState) {
    super.onSaveInstanceState(outState);
    // same as you do
}

answered Mar 25 '13 at 19:09

Mr_and_Mrs_D

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Android: ListView not loading items after orientation change

2 Answers2