我目前有一项活动需要从Parse数据库中获取数据。仅当本地数据存储区为空时才应该进行提取。我尝试创建一个asynctask以及使用if-else块，但是，在获取数据之前，控件会跳转到下一行代码，导致应用程序崩溃。我该如何做到这一点？ 这是代码：
public class Splash extends AppCompatActivity {
ArrayList<String> Titles = new ArrayList<>();
ArrayList<String> Descriptions = new ArrayList<>();
ArrayList<String> VideoIDs = new ArrayList<>();
ArrayList<String> FullUrls = new ArrayList<>();
ArrayList<String> IDsForYTsdk = new ArrayList<>();
String lang, objCode;// englishObject, hindiObject ;
Intent intent;
Firebase myFirebaseRef;
ParseQuery<ParseObject> query = ParseQuery.getQuery("class");
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_splash);
Window window = getWindow();
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
window.clearFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS);
window.addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
window.setStatusBarColor(Color.parseColor("#512DA8"));
}
checkFirstRun() /if first run, fetch from database
try {
FileInputStream fis = openFileInput(getResources().getString(R.string.FILENAME));
BufferedReader br = new BufferedReader(new InputStreamReader(fis));
String c;
lang = "";
while ((c = br.readLine()) != null) {
lang = lang + c;
}
br.close();
fis.close();
} catch (Exception e) {
e.printStackTrace();
}
intent = new Intent(Splash.this, MainActivity.class);
Thread timer = new Thread() {
@Override
public void run() {
super.run();
//final ParseQuery<ParseObject> query = ParseQuery.getQuery("class"); //GET PARSEOBJECTS LIST FROM SERVER
try {
ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
if (networkInfo != null && networkInfo.isConnected()) {
//query.fromLocalDatastore(); //so user doesnt have to wait
query.whereExists("youtube_id");
query.setLimit(30);
query.orderByDescending("updatedAt");
if (lang.equals("en"))
query.whereEqualTo("language", "en");
else if (lang.equals("hi"))
query.whereEqualTo("language", "hi");
query.findInBackground(new FindCallback<ParseObject>() {
public void done(final List<ParseObject> idList, ParseException e) {
if (e == null) {
for (int i = 0; i < idList.size(); i++) {
Titles.add(i, idList.get(i).get("video_title").toString());
Descriptions.add(i, idList.get(i).get("video_script").toString());
VideoIDs.add(i, "https://www.youtube.com/embed/" + idList.get(i).get("youtube_id").toString() + "?rel=0&controls=0&showinfo=0&autoplay=1&modestbranding=1");
IDsForYTsdk.add(i, YouTubeUrlParser.getVideoId(VideoIDs.get(i)));
FullUrls.add(i, "https://youtu.be/" + IDsForYTsdk.get(i));
}
//Toast.makeText(getApplicationContext(), "IDs weren't same", Toast.LENGTH_SHORT).show();
intent.putStringArrayListExtra("titles", Titles);
intent.putStringArrayListExtra("descs", Descriptions);
intent.putStringArrayListExtra("videoIds", VideoIDs);
intent.putStringArrayListExtra("idsForSDK", IDsForYTsdk);
intent.putStringArrayListExtra("links", FullUrls);
ParseObject.unpinAllInBackground("objectsID", idList, new DeleteCallback() {
public void done(ParseException e) {
if (e != null) {
return;
}
ParseObject.pinAllInBackground(idList);
}
});
startActivity(intent);
} else {
e.printStackTrace();
Toast.makeText(getApplicationContext(), "Couldn't fetch data", Toast.LENGTH_SHORT).show();
}
}
});
} else {
query.fromLocalDatastore();
query.orderByDescending("updatedAt");
if (lang.equals("en"))
query.whereEqualTo("language", "en");
else if (lang.equals("hi"))
query.whereEqualTo("language", "hi");
query.findInBackground(new FindCallback<ParseObject>() {
public void done(final List<ParseObject> idList, ParseException e) {
if (e == null) {
for (int i = 0; i < idList.size(); i++) {
Titles.add(i, idList.get(i).get("video_title").toString());
Descriptions.add(i, idList.get(i).get("video_script").toString());
VideoIDs.add(i, "https://www.youtube.com/embed/" + idList.get(i).get("youtube_id").toString() + "?rel=0&controls=0&showinfo=0&autoplay=1");
IDsForYTsdk.add(i, YouTubeUrlParser.getVideoId(VideoIDs.get(i)));
FullUrls.add(i, "https://youtu.be/" + IDsForYTsdk.get(i));
}
intent.putStringArrayListExtra("titles", Titles);
intent.putStringArrayListExtra("descs", Descriptions);
intent.putStringArrayListExtra("videoIds", VideoIDs);
intent.putStringArrayListExtra("links", FullUrls);
intent.putStringArrayListExtra("idsForSDK", IDsForYTsdk);
//intent.putStringArrayListExtra("language", Language);
Toast.makeText(getApplicationContext(), "Fetched saved data", Toast.LENGTH_SHORT).show();
startActivity(intent);
} else {
e.printStackTrace();
Toast.makeText(getApplicationContext(), "Couldn't fetch saved data", Toast.LENGTH_SHORT).show();
}
}
});
}
} catch (Exception e) {
e.printStackTrace();
}
}
};
timer.start();
}
public void checkFirstRun() {
boolean isFirstRun = getSharedPreferences("PREFERENCE", MODE_PRIVATE).getBoolean("isFirstRun", true);
if (isFirstRun) {
ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
if (networkInfo != null && networkInfo.isConnected()) {
try {
FileOutputStream fos = openFileOutput(getResources().getString(R.string.FILENAME), Context.MODE_PRIVATE);
fos.write(getResources().getString(R.string.ENGLISH).getBytes());
fos = openFileOutput(getResources().getString(R.string.storeEnObjFile), Context.MODE_PRIVATE);
fos.write(getResources().getString(R.string.objEN).getBytes());
fos = openFileOutput(getResources().getString(R.string.storeHiObjFile), Context.MODE_PRIVATE);
fos.write(getResources().getString(R.string.objHI).getBytes());
fos.close();
//Toast.makeText(this, "File created", Toast.LENGTH_SHORT).show();
setUpAppOnFirstLaunch();
FirebaseCode();
} catch (Exception fne) {
fne.printStackTrace();
}
getSharedPreferences("PREFERENCE", MODE_PRIVATE)
.edit()
.putBoolean("isFirstRun", false)
.apply();
} else {
Toast.makeText(this, "Please connect to a network and try again.", Toast.LENGTH_LONG).show();
finish();
}
}
}
private void setUpAppOnFirstLaunch() {
query.whereExists("youtube_id");
query.setLimit(30);
query.orderByDescending("updatedAt");
if (lang.equals("en"))
query.whereEqualTo("language", "en");
else if (lang.equals("hi"))
query.whereEqualTo("language", "hi");
query.findInBackground(new FindCallback<ParseObject>() {
public void done(final List<ParseObject> idList, ParseException e) {
if (e == null) {
for (int i = 0; i < idList.size(); i++) {
Titles.add(i, idList.get(i).get("video_title").toString());
Descriptions.add(i, idList.get(i).get("video_script").toString());
VideoIDs.add(i, "https://www.youtube.com/embed/" + idList.get(i).get("youtube_id").toString() + "?rel=0&controls=0&showinfo=0&autoplay=1");
IDsForYTsdk.add(i, YouTubeUrlParser.getVideoId(VideoIDs.get(i)));
FullUrls.add(i, "https://youtu.be/" + IDsForYTsdk.get(i));
}
//Toast.makeText(getApplicationContext(), "IDs weren't same", Toast.LENGTH_SHORT).show();
intent.putStringArrayListExtra("titles", Titles);
intent.putStringArrayListExtra("descs", Descriptions);
intent.putStringArrayListExtra("videoIds", VideoIDs);
intent.putStringArrayListExtra("links", FullUrls);
intent.putStringArrayListExtra("idsForSDK", IDsForYTsdk);
ParseObject.unpinAllInBackground("objectsID", idList, new DeleteCallback() {
public void done(ParseException e) {
if (e != null) {
return;
}
ParseObject.pinAllInBackground(idList);
}
});
startActivity(intent);
} else {
e.printStackTrace();
Toast.makeText(getApplicationContext(), "Couldn't fetch data", Toast.LENGTH_SHORT).show();
}
}
});
}
答案 0 :(得分：1)
如果您使用的是 AsyncTask ，请覆盖其onPostExecute方法，并在调用完成后放置您想要执行的任何方法。
如果您使用解析后台任务，则覆盖done()方法并放置您想要执行的任何方法。
很难给你一个特定的代码，你的代码......非常混乱，难以阅读。所以请记住以上提示并尝试一下。
答案 1 :(得分：1)
我不知道如果这是正确的方法，但它对我有用。
如果在从AsyncTask完成检查后必须执行某些操作
执行onPostExecute
async Task.（）的下一行
如果您没有访问任何GUI组件，您可以在doOnBackground的末尾写下您必须执行的下一行（即使在您的情况下不会被调用） asyncTask