Android：AsyncTask onPostExecute 得到空回复

Question

我正在开发一个 Android 应用程序，我在该应用程序中使用 AsyncTask 与活动在同一类中。在我有一个线程模型之前，我会加入线程并等到我得到回复。但是由于它锁定了 UI，我正在将我的代码迁移到异步任务。其他方法进展顺利，但我收到一个错误，没有收到任何内容。

由于服务器本身位于本地主机中，因此我正在记录我发送了回复。此外，它可以很好地与 Thread 配合使用。我做错了什么？

错误日志：

10-14 13:47:00.917 31746-31746/internetlegion.twentynotes E/AndroidRuntime: FATAL EXCEPTION: main
10-14 13:47:00.917 31746-31746/internetlegion.twentynotes E/AndroidRuntime: Process: internetlegion.twentynotes, PID: 31746
10-14 13:47:00.917 31746-31746/internetlegion.twentynotes E/AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object org.springframework.http.ResponseEntity.getBody()' on a null object reference
10-14 13:47:00.917 31746-31746/internetlegion.twentynotes E/AndroidRuntime:     at internetlegion.twentynotes.Activity.GroupAccountActivity$getGroupAccountsForLoggedInUser.onPostExecute(GroupAccountActivity.java:125)
10-14 13:47:00.917 31746-31746/internetlegion.twentynotes E/AndroidRuntime:     at internetlegion.twentynotes.Activity.GroupAccountActivity$getGroupAccountsForLoggedInUser.onPostExecute(GroupAccountActivity.java:108)
10-14 13:47:00.917 31746-31746/internetlegion.twentynotes E/AndroidRuntime:     at android.os.AsyncTask.finish(AsyncTask.java:632)
10-14 13:47:00.917 31746-31746/internetlegion.twentynotes E/AndroidRuntime:     at android.os.AsyncTask.access$600(AsyncTask.java:177)
10-14 13:47:00.917 31746-31746/internetlegion.twentynotes E/AndroidRuntime:     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
10-14 13:47:00.917 31746-31746/internetlegion.twentynotes E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:102)
10-14 13:47:00.917 31746-31746/internetlegion.twentynotes E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:155)
10-14 13:47:00.917 31746-31746/internetlegion.twentynotes E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5696)
10-14 13:47:00.917 31746-31746/internetlegion.twentynotes E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method)
10-14 13:47:00.917 31746-31746/internetlegion.twentynotes E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Method.java:372)
10-14 13:47:00.917 31746-31746/internetlegion.twentynotes E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1028)
10-14 13:47:00.917 31746-31746/internetlegion.twentynotes E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:823)

GroupAccountActivity：

public class GroupAccountActivity extends Activity {

    private ResponseEntity<RestGroupAccount[]> responseEntity;

    GroupAccountAdapter groupAccountAdapter;

    final String groupAccountRetrieveURL = StaticRestTemplate.baseURL+"getgroupsforuser/";
 @Override
    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_group_account);

        if(isOnline()) {
            new getGroupAccountsForLoggedInUser().execute();
        }else {
            Toast.makeText(getApplicationContext(),"No Internet connection",Toast.LENGTH_LONG).show();
        }
}
  public class getGroupAccountsForLoggedInUser extends AsyncTask<Void,Void,ResponseEntity<RestGroupAccount[]>>{

        @Override
        protected ResponseEntity<RestGroupAccount[]> doInBackground(Void... params) {
            RestTemplate restTemplate = StaticRestTemplate.getRest();
            HttpHeaders requestHeaders = new HttpHeaders();
            requestHeaders.add("Cookie", "JSESSIONID=" + StaticRestTemplate.jsessionid);
            requestHeaders.setAccept(Collections.singletonList(new MediaType("application", "json")));
            HttpEntity<?> requestEntity = new HttpEntity<Object>(requestHeaders);
            restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
            return restTemplate.exchange(groupAccountRetrieveURL, HttpMethod.GET, requestEntity, RestGroupAccount[].class);
        }

        @Override
        protected void onPostExecute(ResponseEntity<RestGroupAccount[]> entity) {
            super.onPostExecute(entity);
// Line below is throwing error.
            RestGroupAccount[] restGroupAccounts = responseEntity.getBody();
            Collections.addAll(restGroupAccountList, restGroupAccounts);

            ArrayList<HashMap<String, String>> groupList = new ArrayList<HashMap<String, String>>();
}

}

请告诉我。非常感谢。 :-)

Answer 1

您在 onPostExecute 中引用了错误的对象。您应该引用结果对象/参数。

将您的代码更改为：

RestGroupAccount[] restGroupAccounts = entity.getBody();

Answer 2

responseEntity 永远不会初始化。

我想你想做

RestGroupAccount[] restGroupAccounts = entity.getBody();

Answer 3

我想我发现了错误。你要做的是

RestGroupAccount[] restGroupAccounts = responseEntity.getBody();

但在 onPostExecute 中，响应称为entity。

您在上面声明了 responseEntity，例如：

private ResponseEntity<RestGroupAccount[]> responseEntity;

但是那个不包含响应。

尝试改变

RestGroupAccount[] restGroupAccounts = responseEntity.getBody();

到

RestGroupAccount[] restGroupAccounts = entity.getBody();