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POAsyncTask updating UI
 

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    <p>So many hours trying to figure this out, I have read so many questions, forums, answers.. but it still will not update the UI.</p> <p>My end goal is to take a search term from user, and send a httprequest to PHP scrip that replies with JSON. This works fine so I will not delve into it.</p> <p>My problem is then updating the UI after this is done. I can get the HTTP results, but for now, I am just trying to update the UI with a basic string before implementing the big changes such as buttons with listeners etc with all the results. For now, just simple String addition to the UI.</p> <p>The onPreExecute() adds a string to the UI and this works fine somehow, as implemented below.</p> <p>The problem is in onPostExecute.. like I said, for now, just a String, to test (it will be a list or something eventually). It doesn't work at all, always throwing exception.</p> <pre><code>public class DisplaySearchActivity extends ListActivity { ArrayList&lt;String&gt; listItems=new ArrayList&lt;String&gt;(); ArrayAdapter&lt;String&gt; adapter = null; private class updateUI extends AsyncTask&lt;String, Void, String&gt;{ @Override protected void onPreExecute() { listItems.add("Retrieving Results..."); // This actually works just like that } @Override protected String doInBackground(String... message) { final List&lt;HashMap&lt;String,String&gt;&gt; blist = httpSearch.search(message[0]); return "It has done"; } @Override protected void onPostExecute(String b){ Log.v("ok", "shane - "+ b); listItems.add("Business: "+ b); adapter.notifyDataSetChanged(); } } @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_display_search); final ArrayAdapter&lt;String&gt; adapter = new ArrayAdapter&lt;String&gt;(this,android.R.layout.simple_list_item_1,listItems); setListAdapter(adapter); // final String message = getIntent().getStringExtra("input"); final String message = "third+level"; new updateUI().execute(message); } // end onCreate } </code></pre> <p>Here is the exception</p> <pre><code>03-15 13:38:41.190: V/ok(15732): shane - It has done 03-15 13:38:41.190: D/AndroidRuntime(15732): Shutting down VM 03-15 13:38:41.190: W/dalvikvm(15732): threadid=1: thread exiting with uncaught exception (group=0x4142a2a0) 03-15 13:38:41.200: E/AndroidRuntime(15732): FATAL EXCEPTION: main 03-15 13:38:41.200: E/AndroidRuntime(15732): java.lang.NullPointerException 03-15 13:38:41.200: E/AndroidRuntime(15732): at ie.whereis.DisplaySearchActivity$updateUI.onPostExecute(DisplaySearchActivity.java:34) 03-15 13:38:41.200: E/AndroidRuntime(15732): at ie.whereis.DisplaySearchActivity$updateUI.onPostExecute(DisplaySearchActivity.java:1) 03-15 13:38:41.200: E/AndroidRuntime(15732): at android.os.AsyncTask.finish(AsyncTask.java:631) 03-15 13:38:41.200: E/AndroidRuntime(15732): at android.os.AsyncTask.access$600(AsyncTask.java:177) 03-15 13:38:41.200: E/AndroidRuntime(15732): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644) 03-15 13:38:41.200: E/AndroidRuntime(15732): at android.os.Handler.dispatchMessage(Handler.java:99) 03-15 13:38:41.200: E/AndroidRuntime(15732): at android.os.Looper.loop(Looper.java:137) 03-15 13:38:41.200: E/AndroidRuntime(15732): at android.app.ActivityThread.main(ActivityThread.java:4898) 03-15 13:38:41.200: E/AndroidRuntime(15732): at java.lang.reflect.Method.invokeNative(Native Method) 03-15 13:38:41.200: E/AndroidRuntime(15732): at java.lang.reflect.Method.invoke(Method.java:511) 03-15 13:38:41.200: E/AndroidRuntime(15732): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1006) 03-15 13:38:41.200: E/AndroidRuntime(15732): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:773) 03-15 13:38:41.200: E/AndroidRuntime(15732): at dalvik.system.NativeStart.main(Native Method) </code></pre> <p>I think it is being thrown by the line:</p> <pre><code>adapter.notifyDataSetChanged(); </code></pre> <p>But I just don't really understand what the adapter does, even after much reading. I don't know why the </p> <pre><code>listItems.add("Retrieving Results..."); </code></pre> <p>in pre Execute works :S but the one in post does not.</p> <p>Any help is so greatly appreciated.</p> <hr> <p>Thank you, I have commented the solution. Apologies for not being able to deal out up votes. &lt;15 karma</p>
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    1. COI had adapter instanciated twice it seems was the issue, and upon removing the final ArrayAdapter<String> as was suggested, the problem has been solved.. Thank you beautiful brains out there!
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