为什么我的 UI 仅在 AsyncTask 完成后显示？

Question

我在我的MainActivity 中放置了一个名为RetrieveHttp 的子类扩展AsycTask，它应该在后台进行一些处理。

活动应按以下方式工作： 显示 UI，启动后台任务（检索 URL，将内容解析为字符串数组），当 AsyncTask 完成后，它应该在 UI 上创建一个 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，UI 才会显示，同时用户只会看到黑屏。请您给我一些建议，我的代码有什么问题？

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

因为这条线

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

get 方法等待异步任务完成，基本上否定了异步任务应该做的事情。

删除get并在异步任务的onPostExecute中设置您的questions，UI将正常显示