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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);
    }

}

}

和日志猫：

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
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1 回答 1

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)

你在班级的第 46 行有一个 NPE。发布的代码显然缺少一些行，但我想如果出现任何问题，String phrase = response.getStatusLine().getReasonPhrase();就是这一行responsenullhttpclient.execute(request);

因此，只需将该行也放入块中，并在方法的末尾try/catch添加一个简单的代替。return null;

于 2012-09-28T13:02:15.207 回答