android - 在调用 onPause() 后，如何停止在后台 android 中循环的异步任务？
问题描述
我正在使用包 com.hierynomus.smbj.share；通过 smb2 连接到网络位置以检查其连接性，但这仅在我的活动开始时运行（在后台）。
一旦调用活动中的侦听器（我从中调用任务），我添加了一个侦听器以在任务返回字符串值（失败，成功）后返回，然后创建连接状态的新实例（此循环它）
这就是我在活动的 onCreate() 处检查连接的方式
//Global ConnectionStatus connectionStatus;
connectionStatus = new ConnectionStatus();
connectionStatus.setContext(this);
connectionStatus.setListener(this);
connectionStatus.setCon(databaseReadWrite.getMydbc());
connectionStatus.execute("CheckDatabase", "nodelay");
这就是我在打开另一个活动时尝试取消任务的方式
protected void onPause() {
delay.equals("cancel");
super.onPause();
MyApplication.activityPaused();
if (connectionStatus != null) {
connectionStatus.cancel(true);
}
hasRun = false;
}
然后在异步任务完成后在同一个活动中运行，所以我重新运行了一个新的 connectionStatus 实例
@Override
public void onTaskCompleted(String result) {
ActionBar actionBar = this.getSupportActionBar();
String title = getTitle().toString();
String code = handlingFunctions.getResultCode(result);
if (code.equals("1")) {
Message.message(this, " Database connected to server!");
setTitle(title + result);
} else if (code.equals("2")) {
actionBar.setBackgroundDrawable(new ColorDrawable(Color.RED));
alertDialog.message(this, result);
} else if (code.equals("0")) {
actionBar.setBackgroundDrawable(new ColorDrawable(Color.RED));
setTitle(title + " Database connected in offline mode");
alertDialog.message(this, result);
} else if (code.equals("3")) {
//alertDialog.message(this, result);
imageStatus.setText(result);
} else if (code.equals("4")) {
imageStatus.setText(result);
}
connectionStatus = new ConnectionStatus();
connectionStatus.setContext(getApplicationContext());
connectionStatus.setListener(AllParts.this);
connectionStatus.setCon(databaseReadWrite.getMydbc());
connectionStatus.execute("CheckDatabase", "delay");
}
}
public class ConnectionStatus extends AsyncTask<String, Void, String> {
private OnConnectionStatusComplete listener;
private ArrayList<String> imageNames;
private ArrayList<ImageDetails> currentImageDetails;
private SQLiteConnection sqLiteConnection;
private Context context;
public void setListener(OnConnectionStatusComplete listen) {
this.listener = listen;
}
public void setImageNames(ArrayList<String> ImageNames) {
this.imageNames = ImageNames;
}
public void setCurrentDetails(ArrayList<ImageDetails> details) {
this.currentImageDetails = details;
}
@Override
protected void onPostExecute(String s) {
listener.onTaskCompleted(s);
}
public void setContext(Context mContext) {
context = mContext;
}
public void setCon(SQLiteConnection sqlite) {
sqLiteConnection = sqlite;
}
@Override
protected String doInBackground(String... strings) {
if(this.isCancelled()){
return "";
}else{
MyApplication myApplication = (MyApplication) context.getApplicationContext();
String IPAddress = myApplication.getIpaddress();
String domain = myApplication.getDomainname();
String username = myApplication.getUsername();
String password = myApplication.getPassword();
String containingFolder = myApplication.getSharefolder();
String temp = "";
//return null;
if (strings[1].equals("delay")) {
try {
Thread.sleep(6000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
if (strings[0].equals("CheckDatabase")) {
temp = checkDatabaseConnect();
} else {
temp = checkImageConnection(IPAddress, domain, username, password, containingFolder);
}
return temp;
}
}
String checkDatabaseConnect() {
String statement = "PRAGMA sync_status";
JSONArray is_ready = new JSONArray();
try {
SQLiteStatement mystatement = null;
try {
mystatement = sqLiteConnection.prepareStatement(statement);
} catch (SQLException ex) {
try {
java.io.File path = new java.io.File("/sdcard/exports/logs");
SimpleDateFormat dateFormat = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");
String currentDateTime = dateFormat.format(new Date()) + " ";
java.io.File myFile = new java.io.File(path, "DBCrashes.txt");
FileOutputStream fOut = new FileOutputStream(myFile, true);
OutputStreamWriter myOutWriter = new OutputStreamWriter(fOut);
myOutWriter.append("\n" +
"\r");
myOutWriter.append(currentDateTime + "Get pragma results: (" + statement + ")" + ex);
myOutWriter.close();
fOut.close();
} catch (java.io.IOException e) {
//do something if an IOException occurs.
}
}
mystatement.step();
int ncols = mystatement.getColumnCount();
if (ncols > 0) {
String result = mystatement.getColumnTextNativeString(0);
JSONObject jObject = new JSONObject(result);
is_ready = jObject.getJSONArray("peers");
if (is_ready.length() > 0) {
return "Success, Database is connected! (1)";
} else {
return "The database is not connected to the server. In offline mode, check network and restart application to connect to server. (0)";
}
}
mystatement.dispose();
} catch (SQLException ex) {
try {
java.io.File path = new java.io.File("/sdcard/exports/logs");
SimpleDateFormat dateFormat = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");
String currentDateTime = dateFormat.format(new Date()) + " ";
java.io.File myFile = new java.io.File(path, "DBCrashes.txt");
FileOutputStream fOut = new FileOutputStream(myFile, true);
OutputStreamWriter myOutWriter = new OutputStreamWriter(fOut);
myOutWriter.append("\n" +
"\r");
myOutWriter.append(currentDateTime + " (" + statement + ")" + ex);
myOutWriter.close();
fOut.close();
return "No connection to a database, please try again (2)";
} catch (java.io.IOException e) {
//do something if an IOException occurs.
}
} catch (JSONException e) {
e.printStackTrace();
}
return "Success (5)";
}
}
我遇到的问题是在我离开活动后，任务仍在运行并返回此错误（我知道这是因为它考虑了延迟）
解决方案
您确实已经实现了对 isCanceled 的处理，但这个实现只是在开始。
您当前的流程是这样的：
- 任务开始，立即检查它是否被取消（因为它是 doInBackground 中的第一行）
- onPause 被调用，任务的取消被调用
- 由于已经进行了取消检查，您的任务将继续自由运行
你如何解决这个问题？
最简单的方法是在调用 checkDatabaseConnection 或 checkImageConnection 之前检查它是否被取消。甚至在这些方法中检查它是否被取消。
即使正确完成，您的 Thread.sleep 也可能导致您的 AsyncTask 在调用 onPause 后 6 秒被取消。
由于这样的原因，不再使用 AsyncTask。线程还有其他更好的选择。