在 Android 中搜索时显示进度对话框

Question

我阅读了 stackoverflow 上的所有问题，这些问题可以给我一个提示，但我无法让它工作。

我拥有的：

我有一个名为“wantlist”的活动，它启动我的应用程序。在此活动中，我有一个按钮，可以通过 onSearchRequested() 开始搜索；

我有另一个名为“discogssearch”的活动，它调用互联网上的 XML Api、解析数据并显示搜索结果。

所有这一切都运行良好。

我想要实现的目标：

我想在发出耗时的 api 调用时显示 ProgessDialog。

我尝试过的：

在搜索开始之前，我尝试通过多种方式打开 ProgessDialog 并发现，我必须与主线程异步执行此操作。所以我把耗时的代码放入AsyncTask中并启动它。

发生了什么：

当我输入文本并按回车键时，什么也没有发生（像以前一样），直到结果到达。现在“discogssearch”透视图与结果一起显示，并且进度对话框显示，但此时所有工作都已完成。

我的代码：

wantlist.java

public class wantlist extends Activity implements OnClickListener {
/** Called when the activity is first created. */

ArrayList<Want> wants = new ArrayList<Want>();

@Override
public void onCreate(Bundle savedInstanceState) {        

    wants.add(new Want("Want1"));
    wants.add(new Want("Want2"));
    wants.add(new Want("Want3"));
    wants.add(new Want("Want4"));
    wants.add(new Want("Want5"));

    super.onCreate(savedInstanceState);

    setContentView(R.layout.main);

    ListView lv = (ListView) findViewById(R.id.WantList); 
    ImageButton b = (ImageButton) findViewById(R.id.searchbutton);
    b.setOnClickListener(this);

    lv.setAdapter(new WantAdapter(this,
            R.layout.lplistitem, wants));
    lv.setTextFilterEnabled(true);

}

public void onClick(View v) {
    onSearchRequested();

}

}

discogssearch.java

public class discogssearch extends Activity implements OnItemClickListener{
/** Called when the activity is first created. */

private static final int PROGRESS_DIALOG = 0;
private static final String LOGTAG = discogssearch.class.getName();

@Override
  public void onAttachedToWindow() {
    super.onAttachedToWindow();
    Window window = getWindow();
    // Eliminates color banding
    window.setFormat(PixelFormat.RGBA_8888);
  }


private ListView alv = null;
private ListView rlv = null;
private ListView llv = null;

ArrayList<Want> results = new ArrayList<Want>();
View.OnTouchListener gestureListener;
GestureDetector pageFlip;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.searchresults);

    Intent intent = getIntent();


      String query = intent.getStringExtra(SearchManager.QUERY);

      searchDiscogs(query);

}

public void searchDiscogs(String query)
{   
    query = URLEncoder.encode(query);
    alv = (ListView) findViewById(R.id.ArtistList);
    rlv = (ListView) findViewById(R.id.ReleaseList);
    llv = (ListView) findViewById(R.id.LabelList);

    rlv.setOnItemClickListener(this);

    rlv.setFastScrollEnabled(true);
    rlv.setVerticalFadingEdgeEnabled(true);

    results.clear();


    AsyncTask<String, Integer, DiscogsXMLHandler> at = new AsyncDiscogsSearch().execute(query);
    DiscogsXMLHandler discogsHandler = null;

    try {
        discogsHandler = at.get();
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (ExecutionException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    Log.d("WICHTIG: ",discogsHandler.getReleaseResults().size() + "");

    alv.setAdapter(new WantAdapter(this,
            R.layout.lplistitem, discogsHandler.getArtistResults()));

    rlv.setAdapter(new WantAdapter(this,
            R.layout.lplistitem, discogsHandler.getReleaseResults()));

    llv.setAdapter(new WantAdapter(this,
            R.layout.lplistitem, discogsHandler.getLabelResults()));
}

public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
        long arg3) {

    if(arg0.equals(rlv))
    {
        String uri = ((Want)rlv.getItemAtPosition(arg2)).getDetailsUri();
        Log.d("Itemclick", uri);
        Intent viewUri = new Intent("android.intent.action.VIEW", Uri.parse(uri));
        viewUri.setClass(this, releasedetails.class);
        startActivity(viewUri);
    }


}

public Dialog onCreateDialog(int dial)
{

    switch(dial) {
    case PROGRESS_DIALOG:
        Log.d(LOGTAG,"Showing Progress Dialog");
        ProgressDialog progressDialog = new ProgressDialog(this);
        progressDialog.setMessage("Loading...");
        return progressDialog;
    default:
        return null;
    }
}

private Animation inFromRightAnimation() {
      Animation inFromRight = new TranslateAnimation(
        Animation.RELATIVE_TO_PARENT, +1.0f,
        Animation.RELATIVE_TO_PARENT, 0.0f,
        Animation.RELATIVE_TO_PARENT, 0.0f,
        Animation.RELATIVE_TO_PARENT, 0.0f);
      inFromRight.setDuration(100);
      inFromRight.setInterpolator(new AccelerateInterpolator());
      return inFromRight;
     }

     private Animation outToLeftAnimation() {
      Animation outtoLeft = new TranslateAnimation(
        Animation.RELATIVE_TO_PARENT, 0.0f,
        Animation.RELATIVE_TO_PARENT, -1.0f,
        Animation.RELATIVE_TO_PARENT, 0.0f,
        Animation.RELATIVE_TO_PARENT, 0.0f);
      outtoLeft.setDuration(100);
      outtoLeft.setInterpolator(new AccelerateInterpolator());
      return outtoLeft;
     }

     private Animation inFromLeftAnimation() {
      Animation inFromLeft = new TranslateAnimation(
        Animation.RELATIVE_TO_PARENT, -1.0f,
        Animation.RELATIVE_TO_PARENT, 0.0f,
        Animation.RELATIVE_TO_PARENT, 0.0f,
        Animation.RELATIVE_TO_PARENT, 0.0f);
      inFromLeft.setDuration(100);
      inFromLeft.setInterpolator(new AccelerateInterpolator());
      return inFromLeft;
     }

     private Animation outToRightAnimation() {
      Animation outtoRight = new TranslateAnimation(
        Animation.RELATIVE_TO_PARENT, 0.0f,
        Animation.RELATIVE_TO_PARENT, +1.0f,
        Animation.RELATIVE_TO_PARENT, 0.0f,
        Animation.RELATIVE_TO_PARENT, 0.0f);
      outtoRight.setDuration(100);
      outtoRight.setInterpolator(new AccelerateInterpolator());
      return outtoRight;
     }

     private class AsyncDiscogsSearch extends AsyncTask<String, Integer, DiscogsXMLHandler>{

            public static final String APIKEY = "xxxxxxxx";
            private final ProgressDialog pg = new ProgressDialog(discogssearch.this);

            @Override
            protected DiscogsXMLHandler doInBackground(String... params) {

                String urlString = "http://www.discogs.com/search?type=all&q="+params[0]+"&f=xml&api_key="+APIKEY ;

                //Retrieve XML-Data as InputStream
                InputStream instream = GZipStreamHelper.getStream(urlString);

                //Parse XML-Data
                DiscogsXMLHandler discogsHandler = new DiscogsXMLHandler();
                XMLParsingHelper.getInstance().parseAndHandle(instream, discogsHandler);

                return discogsHandler;
            }

            @Override
            protected void onPostExecute(DiscogsXMLHandler result) {
                // TODO Auto-generated method stub
                pg.dismiss();
            }

            @Override
            protected void onPreExecute() {
                pg.show();
            }




        }

}

感谢您的任何建议！

Answer 1

据我了解，您的行 discogsHandler = at.get(); 会阻塞您的 UI 线程。 onPreExecute 被执行，但这只会将进度对话框放入主线程的消息循环中。但是，实际打开和处理对话框的代码是在从 searchDiscogs() 返回后执行的。

解决方案是将查询结果的处理放入 AsyncTask 中 < code>onPostExecute，或从那里调用结果处理方法。

Answer 2

我认为 user634618 是正确的。 AsyncTask#get()指出：

必要时等待计算完成，然后检索其结果。

（强调是后加的）。因此，UI 线程只是停留在对 get 的调用处，并且您失去了执行 AsyncTask 的意义。由于 UI 线程被阻塞，因此您显示进度对话框的请求不会被执行。

正如 user634618 所建议的，您可以在 onPostExecute 中处理搜索结果，这将释放 UI 线程并允许显示进度对话框。