Android：在 AsyncTask 上获取 RuntimeException

Question

在代码中，我尝试使用 http 客户端从 Web 服务中读取数据。然后我想将http响应的响应短语写入文本视图。 UI 是通过 onPostExecute() 访问的，所以我不知道为什么会出现这个异常。

这是代码：

public class CustomersScreen extends Activity {

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

public void LoginClicked(View view) {
    new Get_data().execute("http://localhost:51982/WcfDataService1.svc/Genre");
}

private class Get_data extends AsyncTask <String, Void, String> {

    @Override
    protected String doInBackground(String... url) {
        //InputStream instream = null;
        HttpClient httpclient = new DefaultHttpClient();
        HttpGet request = new HttpGet(url[0]);
        HttpResponse response = null;
        try {
            response = httpclient.execute(request);
        } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        String phrase = response.getStatusLine().getReasonPhrase();

        return phrase;
    }

    @Override
    protected void onPostExecute(String phrase) {
        TextView t = (TextView) findViewById(R.id.textView3);
        t.setText(phrase);
    }

}

}

还有日志猫：

09-28 09:43:34.239: E/AndroidRuntime(679): FATAL EXCEPTION: AsyncTask #1
09-28 09:43:34.239: E/AndroidRuntime(679): java.lang.RuntimeException: An error occured while executing doInBackground()
09-28 09:43:34.239: E/AndroidRuntime(679):  at android.os.AsyncTask$3.done(AsyncTask.java:278)
09-28 09:43:34.239: E/AndroidRuntime(679):  at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
09-28 09:43:34.239: E/AndroidRuntime(679):  at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
09-28 09:43:34.239: E/AndroidRuntime(679):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
09-28 09:43:34.239: E/AndroidRuntime(679):  at java.util.concurrent.FutureTask.run(FutureTask.java:137)
09-28 09:43:34.239: E/AndroidRuntime(679):  at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
09-28 09:43:34.239: E/AndroidRuntime(679):  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
09-28 09:43:34.239: E/AndroidRuntime(679):  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
09-28 09:43:34.239: E/AndroidRuntime(679):  at java.lang.Thread.run(Thread.java:856)
09-28 09:43:34.239: E/AndroidRuntime(679): Caused by: java.lang.NullPointerException
09-28 09:43:34.239: E/AndroidRuntime(679):  at com.test.CustomersScreen$Get_data.doInBackground(CustomersScreen.java:46)
09-28 09:43:34.239: E/AndroidRuntime(679):  at com.test.CustomersScreen$Get_data.doInBackground(CustomersScreen.java:1)
09-28 09:43:34.239: E/AndroidRuntime(679):  at android.os.AsyncTask$2.call(AsyncTask.java:264)
09-28 09:43:34.239: E/AndroidRuntime(679):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
09-28 09:43:34.239: E/AndroidRuntime(679):  ... 5 more

Answer 1

Caused by: java.lang.NullPointerException
09-28 09:43:34.239: E/AndroidRuntime(679):  at com.test.CustomersScreen$Get_data.doInBackground(CustomersScreen.java:46)

您在班级的第 46 行有一个 NPE。发布的代码显然缺少一些行，但我想这是String phrase = response.getStatusLine().getReasonPhrase(); 这一行，因为如果httpclient.execute(request); 出现任何问题，response 将是null

因此，只需将该行也放入 try/catch 块中，然后在方法末尾添加一个简单的 return null;。