Java tips for coders, by coders

I am unwell and stuck at home so I decided to dive into my Android app (a new one this time!). I wanted to perform some tasks that could be long running (doubtfully but why freeze the UI thread ever). I want to show a ProgressDialog here but it doesn’t work with the static factory method, ProgressDialog.show(…). I keep getting the same exception again and again.

07-20 22:57:16.445: ERROR/AndroidRuntime(25843): FATAL EXCEPTION: main
07-20 22:57:16.445: ERROR/AndroidRuntime(25843): java.lang.NullPointerException
07-20 22:57:16.445: ERROR/AndroidRuntime(25843):     at android.app.ProgressDialog.onProgressChanged(ProgressDialog.java:318)
07-20 22:57:16.445: ERROR/AndroidRuntime(25843):     at android.app.ProgressDialog.setMax(ProgressDialog.java:233)
07-20 22:57:16.445: ERROR/AndroidRuntime(25843):     at com.codercorp.android.playlist.ExporterTask.onPreExecute(ExporterTask.java:68)
07-20 22:57:16.445: ERROR/AndroidRuntime(25843):     at android.os.AsyncTask.execute(AsyncTask.java:391)
07-20 22:57:16.445: ERROR/AndroidRuntime(25843):     at com.codercorp.android.playlist.PlaylistExporterMain.onClick(PlaylistExporterMain.java:81)
07-20 22:57:16.445: ERROR/AndroidRuntime(25843):     at android.view.View.performClick(View.java:2485)
07-20 22:57:16.445: ERROR/AndroidRuntime(25843):     at android.view.View$PerformClick.run(View.java:9080)
07-20 22:57:16.445: ERROR/AndroidRuntime(25843):     at android.os.Handler.handleCallback(Handler.java:587)
07-20 22:57:16.445: ERROR/AndroidRuntime(25843):     at android.os.Handler.dispatchMessage(Handler.java:92)
07-20 22:57:16.445: ERROR/AndroidRuntime(25843):     at android.os.Looper.loop(Looper.java:130)
07-20 22:57:16.445: ERROR/AndroidRuntime(25843):     at android.app.ActivityThread.main(ActivityThread.java:3683)
07-20 22:57:16.445: ERROR/AndroidRuntime(25843):     at java.lang.reflect.Method.invokeNative(Native Method)
07-20 22:57:16.445: ERROR/AndroidRuntime(25843):     at java.lang.reflect.Method.invoke(Method.java:507)
07-20 22:57:16.445: ERROR/AndroidRuntime(25843):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
07-20 22:57:16.445: ERROR/AndroidRuntime(25843):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
07-20 22:57:16.445: ERROR/AndroidRuntime(25843):     at dalvik.system.NativeStart.main(Native Method)
07-20 23:02:38.425: ERROR/jdwp(25924): Failed sending reply to debugger: Broken pipe

After googling for a good amount of time I came across this bug report in the Android project http://code.google.com/p/android/issues/detail?id=3114. The report’s been up for over two years now but Google hasn’t bothered to fix it (shame!). As is mentioned in the report, the problem is with the update handler variable not being set before the dialog box is shown. The solution is simple, create your own ProgressDialog without using the static factory method.

ProgressDialog progressDialog = new ProgressDialog(PlaylistExporterMain.this);
progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
progressDialog.setCancelable(false);
progressDialog.setIndeterminate(false);
progressDialog.setMax(getListAdapter().getCount());
progressDialog.show();

If you have run across this bug, please go to the bug report and leave a comment, maybe it’ll force Google’s hand into fixing the bug (which requires an addition to the ProgressDialog static factory methods).

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• Android: Progress dialog in a ListActivity using ListView