我有一个通过 SQLite 使用缓存数据填充的 ListView 。加载完成后。在后台，我检查新数据并从 MySQL 数据库获取返回的 JSON 结果。
在我的这个后台task的onPostExecute中，当运行此代码时(下面的代码)，并且当它被循环时(最多50个循环) ，UI 线程被阻塞，并且无法滚动 ListView。这是代码:
if (result.length() != 0) {
JSONArray jArray = new JSONArray(result);
JSONObject json_data = null;
for (int ii = 0; ii < jArray.length(); ii++) {
json_data = jArray.getJSONObject(ii);
item = json_data.getString("item");
cat = json_data.getString("category");
user = json_data.getString("username");
userId = json_data.getLong("user_id");
review = json_data.getString("review");
reviewId = json_data.getLong("review_id");
itemId = json_data.getLong("item_id");
commentCount = json_data.getLong("commentCount");
url = json_data.getString("name");
url = pathUrl + url; // for profile icon
date = json_data.getString("date");
rating = json_data.getDouble("rating");
upVote = json_data.getLong("good");
wiki = json_data.getString("wiki");
watchItems.add(item);
watchCats.add(cat);
watchUsers.add(user);
watchReviews.add(review);
watchUrl.add(url);
watchDateList.add(date);
watchWikiList.add(wiki);
watchItemIdList.add(String.valueOf(itemId));
watchUserIds.add(String.valueOf(userId));
watchReviewId.add(String.valueOf(reviewId));
watchRating.add(String.valueOf(rating));
watchCommentCount.add(String.valueOf(commentCount));
watchUpVote.add(String.valueOf(upVote));
Rateit.haveFollowing = "1";
if (Rateit.isUserLoggedIn == true) {
boolean oldReview = datasource
.getReviewIds(reviewId);
if (!oldReview) {
// Cache Network Items
datasource.createTrendWatch(itemId, item,
review, reviewId, cat, user,
String.valueOf(userId), url, date,
commentCount, rating, upVote, 0,
wiki);
}
}
FollowingItems wti = new FollowingItems(
Long.valueOf(watchItemIdList.get(i)),
watchItems.get(i), watchCats.get(i),
watchReviews.get(i),
Long.valueOf(watchReviewId.get(i)),
watchUsers.get(i),
Long.valueOf(watchUserIds.get(i)),
watchUrl.get(i), watchDateList.get(i),
Long.valueOf(watchCommentCount.get(i)),
Double.valueOf(watchRating.get(i)),
Long.valueOf(watchUpVote.get(i)),
watchWikiList.get(i++));
watchingListObject.add(wti);
}
}
为什么会发生这种情况？我该如何阻止我的代码来防止这种情况发生？我可以做一些优化吗？
编辑:下面有人请求完整的任务代码。
Below repeats the code above but in context with entire task.
public static class FollowingTask extends AsyncTask<String, String, Void> {
protected InputStream is = null;
protected String result = "";
protected String userId;
protected ArrayList<FollowingItems> watchingListObject;
protected Context mContext;
public FollowingTask(Context context) {
mContext = context;
}
@Override
protected void onPreExecute() {
if (mContext != null && (fromRefresh == false)) {
((MainFragmentActivity) mContext)
.setSupportProgressBarIndeterminateVisibility(true);
}
resetLists();
if (PrefActivity.getUserLoggedInStatus(mContext) == true) {
userId = PrefActivity.getLoggedInUserId(mContext);
} else {
userId = "-1";
}
super.onPreExecute();
}
@Override
protected Void doInBackground(String... params) {
datasource.purgeItemWatchingTable();
Log.d("1", "Back");
String url_select = "http://www.---.info/includes_mc_php/featured_watching.php";
HttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url_select);
ArrayList<NameValuePair> param = new ArrayList<NameValuePair>();
param.add(new BasicNameValuePair("user_id", userId));
param.add(new BasicNameValuePair("v2", "true"));
try {
httpPost.setEntity(new UrlEncodedFormEntity(param));
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
// read content
is = httpEntity.getContent();
} catch (Exception e) {
e.printStackTrace();
}
try {
BufferedReader br = new BufferedReader(
new InputStreamReader(is));
StringBuilder sb = new StringBuilder();
String line = "";
while ((line = br.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result = sb.toString();
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
protected void onPostExecute(Void v) {
String pathUrl = Rateit.PROFILE_PIC_URL;
String item, cat, user, review, url, date, following, wiki;
long itemId, reviewId, userId, commentCount, upVote;
double rating;
int i = 0;
watchingListObject = new ArrayList<FollowingItems>();
try {
String c = String.valueOf(result.charAt(0));
if (c.equals("{")) {
JSONObject jsonObject = new JSONObject(result);
following = jsonObject.getString("following");
if (following.equals("0")) {
Rateit.haveFollowing = "0";
}
} else {
if (result.length() != 0) {
JSONArray jArray = new JSONArray(result);
JSONObject json_data = null;
for (int ii = 0; ii < jArray.length(); ii++) {
json_data = jArray.getJSONObject(ii);
item = json_data.getString("item");
cat = json_data.getString("category");
user = json_data.getString("username");
userId = json_data.getLong("user_id");
review = json_data.getString("review");
reviewId = json_data.getLong("review_id");
itemId = json_data.getLong("item_id");
commentCount = json_data.getLong("commentCount");
url = json_data.getString("name");
url = pathUrl + url; // for profile icon
date = json_data.getString("date");
rating = json_data.getDouble("rating");
upVote = json_data.getLong("good");
wiki = json_data.getString("wiki");
watchItems.add(item);
watchCats.add(cat);
watchUsers.add(user);
watchReviews.add(review);
watchUrl.add(url);
watchDateList.add(date);
watchWikiList.add(wiki);
watchItemIdList.add(String.valueOf(itemId));
watchUserIds.add(String.valueOf(userId));
watchReviewId.add(String.valueOf(reviewId));
watchRating.add(String.valueOf(rating));
watchCommentCount.add(String.valueOf(commentCount));
watchUpVote.add(String.valueOf(upVote));
Rateit.haveFollowing = "1";
if (Rateit.isUserLoggedIn == true) {
boolean oldReview = datasource
.getReviewIds(reviewId);
if (!oldReview) {
// Cache Network Items
datasource.createTrendWatch(itemId, item,
review, reviewId, cat, user,
String.valueOf(userId), url, date,
commentCount, rating, upVote, 0,
wiki);
}
}
FollowingItems wti = new FollowingItems(
Long.valueOf(watchItemIdList.get(i)),
watchItems.get(i), watchCats.get(i),
watchReviews.get(i),
Long.valueOf(watchReviewId.get(i)),
watchUsers.get(i),
Long.valueOf(watchUserIds.get(i)),
watchUrl.get(i), watchDateList.get(i),
Long.valueOf(watchCommentCount.get(i)),
Double.valueOf(watchRating.get(i)),
Long.valueOf(watchUpVote.get(i)),
watchWikiList.get(i++));
watchingListObject.add(wti);
Log.d("1", "Post 2");
}
} else {
Rateit.haveFollowing = "2";
}
}
} catch (JSONException e1) {
e1.printStackTrace();
Rateit.haveFollowing = "2";
} catch (ParseException e1) {
e1.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
Log.d("1", "Post COMPLETE");
mPullRefreshListView.onRefreshComplete();
// Reset Trending List on Pull-to-Refresh
if (mContext != null) {
if (watchUsers.size() == 0) {
l.setVisibility(View.VISIBLE);
tv.setTypeface(TypeFace.get(mContext, Rateit.BPREPLAY));
} else {
l.setVisibility(View.GONE);
}
if (mContext != null) {
listView.setAdapter(null);
if (watchItems.size() > 0) {
wAdapter = new FollowingAdapter(mContext,
watchingListObject, TypeFace.get(mContext,
Rateit.BPREPLAY), TypeFace.get(
mContext, Rateit.ROBOTO_LIGHT),
TypeFace.get(mContext, Rateit.ROBOTO_THIN),
TypeFace.get(mContext, Rateit.ROBOTO_REGULAR));
listView.setAdapter(wAdapter);
}
}
}
if (mContext != null && (fromRefresh == false)) {
((MainFragmentActivity) mContext)
.setSupportProgressBarIndeterminateVisibility(false);
MainFragmentActivity.dismissDialog(mContext);
}
fromRefresh = false;
}
}
最佳答案
onPostExecute 在 UI 线程上运行。它会阻塞 UI。 doInBackground 在后台运行。您应该在 doInBackground 中执行繁重的操作(而不是在 onPostExecute 中)
解决方案:您应该将解析等从onPostExecute移至doInBackground，并使用onPostExecute仅将处理后的信息绑定(bind)到用户界面。
关于java - AsyncTask 中的某些内容阻塞了 UI - 导致界面短暂停止，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/21010566/