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我有兩個AsyncTask活動，其唯一的責任是在UI線程上執行一個AsyncTask。其中一個很好，顯示progressBar，並更新ProgressBar消息。這是用於我的SearchActivity，它實際上是一個搜索活動，其中包含用於聲明搜索活動的Google搜索元數據。我創建了AsyncTask的克隆，並且只更改了doInBackground代碼，並且還克隆了SearchActivity並將其命名爲browseActivity。AsyncTask在預執行時不顯示
我開始BrowseActivity的結果在一個類擴展listView當一個項目被點擊。我打算髮生的事情是，AsyncTask的onPreExecute代碼在ListView活動和ListView將啓動onActivityResult的ResultActivity之間顯示progressAar，如SearchActivity所做的那樣。正在調用onPreExcute代碼，但ProgressBar從不顯示。 （我想我正確地運行了它在UI線程？）
這裏是BrowseActivity：
AsyncTask<String, String, ArrayList<SearchResult>> browseTask;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Intent intent = getIntent();
String genreExtra = getIntent().getStringExtra(Genre.BUNDLE_TAG);
if(genreExtra!=null){
genre = Genre.getgenreFromExtra(genreExtra);
}
String categoryExtra = getIntent().getStringExtra(Category.BUNDLE_TAG);
if(categoryExtra!=null){
this.category = Category.getCategoryFromExtra(categoryExtra);
}
final Connector connector = GlobalVars.getCurrentConnector();
Thread browseThread = new Thread(){
@Override
public void run() {
try {
browseTask = connector.browse(BrowseActivity.this, category, genre, 1);
browseTask.execute("");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
runOnUiThread(browseThread);
ArrayList<SearchResult> result = null;
try {
result = browseTask.get();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Bundle queryBundle = new Bundle();
queryBundle.putSerializable(SERIALIZABLE_KEY, result);
Intent i = new Intent();
i.putExtra(BUNDLE_KEY, queryBundle); //Put in our browse results
i.putExtra(Category.BUNDLE_TAG, category.putExtra()); //put our category in return intent
i.putExtra(Genre.BUNDLE_TAG, genre.putExtra()); //put our genre in return intent
setResult(RESULT_OK, i);
finish();
}
這裏是CategoryActivity（擴展ListActivity），其中browseActivity啓動活動：
@Override
protected void onListItemClick(ListView l, View v, final int position, long id) {
super.onListItemClick(l, v, position, id);
Intent i = new Intent(CategorySelectionView.this, BrowseActivity.class);
final Category[] categories = Category.values();
i.putExtra(Category.BUNDLE_TAG, categories[position].putExtra());
i.putExtra(Genre.BUNDLE_TAG, genre.putExtra());
CategorySelectionView.this.startActivityForResult(i, BrowseActivity.RESULT_REQUEST_CODE);
}
// Listen for results.
protected void onActivityResult(int requestCode, int resultCode, Intent data){
// See which child activity is calling us back.
switch (requestCode) {
case BrowseActivity.RESULT_REQUEST_CODE:
// This is the standard resultCode that is sent back if the
// activity crashed or didn't doesn't supply an explicit result.
if (resultCode == RESULT_CANCELED){
}
else {
ArrayList<SearchResult> recentQueryResults = (ArrayList<SearchResult>)data.getBundleExtra(
BrowseActivity.BUNDLE_KEY).getSerializable(BrowseActivity.SERIALIZABLE_KEY);
GlobalVars.setRecentQueryResults(recentQueryResults);
Category category = Category.getCategoryFromExtra(data.getStringExtra(Category.BUNDLE_TAG));
Intent i = new Intent(CategorySelectionView.this, RomListView.class);
i.putExtra(Category.BUNDLE_TAG, category.putExtra());
i.putExtra(Genre.BUNDLE_TAG, genre.putExtra());
startActivity(i);
}
default:
break;
}
}