Question

我在我的RetrieveHttp中放了一个名为AsycTask的子类MainActivity，它应该在后台执行一些处理。

活动应如下工作：显示UI，启动后台任务（检索URL，解析内容到String数组）以及AsyncTask完成后，应该在UI上创建Toast。

不幸的是，UI正在等待doInBackground()方法完成的任务。只有当AsyncTask完成时，才会显示用户界面，同时用户只会看到黑屏。你能给我一些建议吗，我的代码出了什么问题？

public class Splashscreen extends Activity implements OnClickListener {
private String questions[];
//HTTP-Downloader to InputStream
private RetrieveHttp myHttp = new RetrieveHttp();

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

    //..implementing some listeners here, referencing GUI elements

    try {
        questions = myHttp.execute("http://myurl.de").get();
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (ExecutionException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }   
}



@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.hauptmenue, menu);     
    return true;
}

public void onClick(View v) {
    //doing some stuff...
}

public class RetrieveHttp extends AsyncTask<String, Void, String[]> {

    protected void onPreExecute() {
    }

    @Override
    protected String[] doInBackground(String... params) {
        URL url;
        String string = "";
        String[] questions = null;
        InputStream content = null;
        try {
            url = new URL(params[0]);
            content = getInputStreamFromUrl(url.toString());
            try {
                // Stream to String
                string = CharStreams.toString(new InputStreamReader(
                        content, "UTF-8"));
                questions = string.split("#");
            } catch (UnsupportedEncodingException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        return questions;
    }

    protected void onPostExecute(String[] string) {
        Toast.makeText(getApplicationContext(), 
                    "Finished", Toast.LENGTH_LONG).show();
        return;
    }

}

public static InputStream getInputStreamFromUrl(String url) {
    InputStream content = null;
    try {
        HttpClient httpclient = new DefaultHttpClient();
        HttpResponse response = httpclient.execute(new HttpGet(url));
        content = response.getEntity().getContent();
    } catch (Exception e) {
        Log.e("[GET REQUEST]", "Network exception", e);
    }


    return content;
}
}

Answer 1

因为这行

questions = myHttp.execute("http://myurl.de").get();

get方法等待asynctask完成，基本上否定了异步任务的假设。

删除get并在asynctask的questions中设置onPostExecute，UI将显示为正常

为什么我的UI仅在AsyncTask完成时显示？

1 个答案: