Question

我有两个AsyncTask活动，其唯一的职责是在UI线程上执行AsyncTask。其中一个很好用，显示progressBar，并更新ProgressBar消息。这适用于我的SearchActivity，它实际上是一个搜索活动，其中包含用于声明搜索活动的Google搜索元数据。我创建了AsyncTask的克隆，只更改了doInBackground代码，并且还克隆了SearchActivity并将其命名为browseActivity。

我在单击项目时扩展listView的类中启动BrowseActivity的结果。我打算用AsyncTask的onPreExecute代码来显示一个progressBar，就像SearchActivity一样，在ListView活动和ListView将在onActivityResult上启动的ResultActivity之间。正在调用onPreExcute代码，但从不显示ProgressBar。（我以为我在UI线程上正确运行了它？）

这是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();

}

以下是启动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;
        }
    }

Answer 1

首先，你不能在主/ UI线程上运行AsyncTask，这就是重点。当你调用browseTask.execute()时，无论是调用runOnUiThread()，它都会在相应的线程（主要vs后台）上调用它的方法。通过调用runOnUiThread()，您所做的就是将在另一个Runnable中启动它的代码包装起来。我认为这不是你想要的，因为你在调用runOnUiThread()之后试图得到任务的结果，而这个任务还没有运行。 onCreate()中的代码在UI线程上运行，因此必须在其他内容可以运行之前完成，即onPreExecute()的{{1}}。

您应该做的是创建AsyncTask并将AsyncTask之后的所有内容放在runOnUiThread()中。

AsyncTask不显示onPreExecute

1 个答案: