我正在尝试从API中检索一些数据,但我总是在异步任务中获取null。这是我的asynctask:
private class DownloadTask extends AsyncTask<Bundle, Void, List<Topic>> {
@Override
protected void onPreExecute() {
HomeActivity.mProgressBar.setVisibility(View.VISIBLE);
HomeActivity.mProgressBar.setIndeterminate(true);
}
@Override
protected List<Topic> doInBackground(Bundle... params) {
return downloadPhotos(params[0]);
}
@Override
protected void onPostExecute(List<Topic> topics) {
HomeActivity.mProgressBar.setVisibility(View.INVISIBLE);
HomeActivity.mProgressBar.setIndeterminate(false);
Log.d("List Size: ", ""+topics); // 0
adapter = new TopicListAdapter(activity, topics);
RecyclerView.LayoutManager manager = new MyCustomLayoutManager(activity);
recyclerView.setLayoutManager(manager);
recyclerView.setItemAnimator(new DefaultItemAnimator());
recyclerView.setAdapter(adapter);
}
}
检索数据的方法应该将两个数组合并为一个数组,因为我正在从两个地方检索数据:
private List<Topic> downloadPhotos(Bundle params) {
String profileId = activity.getPreferencesManager().getProfileId();
List<Topic> topicsFromMe, topicsFromFriends;
topicsFromFriends = setValuesFromFriends(params);
topicsFromMe = setValuesFromMe(profileId, params);
topicsFromFriends.addAll(topicsFromMe);
sortTopics(topicsFromFriends);
int k = topicsFromFriends.size();
Log.d("List Size: ", "" + topicsFromFriends); // here also 0 for size
if (k > 10)
topicsFromFriends.subList(10, k).clear();
return topicsFromFriends;
}
这里有一种方法,我将值设置为数组列表。奇怪的是,在这种情况下,RecyclerView填充了这个数组,但我没有得到我想要的结果。例如,我应该对此列表进行排序,并仅显示其中的10条记录。
private List<Topic> setValuesFromFriends(final Bundle params) {
final List<Topic> topics = new ArrayList<>();
activity.getSimpleFacebook().getFriends(new OnFriendsListener() {
@Override
public void onComplete(List<Profile> friends) {
for (final Profile profile : friends) {
activity.getSimpleFacebook().get(profile.getId(), "photos/uploaded", params,
new OnActionListener<List<Photo>>() {
@Override
public void onComplete(List<Photo> photos) {
for (final Photo photo : photos) {
// Initialize instance of Topic
final User user = photo.getFrom();
final Topic topic = new Topic();
topic.setCaption(photo.getName());
topic.setImageId(photo.getId());
topic.setCreatedTime(photo.getCreatedTime());
topic.setPostImage(photo.getSource());
topic.setUserId(user.getId());
topic.setName(user.getName());
final Bundle likeParams = new Bundle();
likeParams.putString("fields", "total_count");
likeParams.putString("limit", "100000");
activity.getSimpleFacebook().get(photo.getId(), "likes",
likeParams, new OnActionListener<List<Like>>() {
@Override
public void onComplete(List<Like> likes) {
topic.setNumOfLikes(likes.size());
topics.add(topic);
}
@Override
public void onThinking() {
super.onThinking();
}
});
}
}
});
}
}
});
return topics;
}
答案 0 :(得分:1)
您正在使用AsyncTask。
AsyncTask正在启动另一个Thread(thread1),它正在执行方法doenloadPhotos
。此方法正在调用setValuesFromFriends
,它正在使用方法getFriends
创建另一个线程(thread2)。随着thread2的启动,setValuesFromFriends
中的其余代码将被执行。
以下是它的工作原理:
private List<Topic> setValuesFromFriends(final Bundle params) {
final List<Topic> topics = new ArrayList<>();
//launched process on new thread
return topics; //this is 0 as topics = new ArrayList<>();
}
现在topicsFromFriends = 0
。因此,您将获得输出= 0.
实际上thread1在thread2完成之前执行。由于thread1的输出为0,因此在onPostExecute
无需使用AsyncTask。
您应该将所有必需的代码放在onComplete
的{{1}}内。这样信息将正确显示。您可以在new OnFriendsListener()
之前启动进度条,然后在setValuesFromFriends
。