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我有两个 AsyncTask 活动，它们的唯一职责是在 UI 线程上执行 AsyncTask。其中一个效果很好，显示进度条，并更新进度条消息。这适用于我的 SearchActivity，它实际上是一个带有 Google 搜索元数据的搜索活动，用于声明搜索活动。我创建了 AsyncTask 的克隆，只更改了 doInBackground 代码，还克隆了 SearchActivity 并将其命名为 browseActivity。

我启动 BrowseActivity 以获得在单击项目时扩展 listView 的类的结果。我打算让 AsyncTask 的 onPreExecute 代码在 ListView 活动和 ListView 将在 onActivityResult 启动的 ResultActivity 之间显示一个进度条，就像 SearchActivity 一样。正在调用 onPreExcute 代码，但从不显示 ProgressBar。（我以为我在 UI 线程上运行它正确？）

这是浏览活动：

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();

}

这是开始browseActivity的CategoryActivity（扩展ListActivity）活动：

   @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;
        }
    }
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1 回答 1

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Firstly, you can't run an AsyncTask on the main/UI Thread, that's the whole point. When you call browseTask.execute() its going to call its methods on the appropriate Thread (main vs background), regardless of calling runOnUiThread(). By calling runOnUiThread() all you are doing is wrapping the code that starts it in another Runnable. I think is not what you want since after calling runOnUiThread() you try to get the result of the task, which hasn't run yet. The code in onCreate() runs on the UI thread, so this has to finish before something else can run, namely the onPreExecute() of the AsyncTask.

What you should be doing is to create the AsyncTask and put everything you currently have after runOnUiThread() in onPostExecute().

于 2011-08-04T21:02:09.353 回答