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[英]How to prevent users from being asked to re-login when closing the app using SharedPreferences and Firebase Authentication
[英]How to prevent a Fragment from being added when an Activity is closing
我正在创建一个与Service
进行通信的Activity
,以通过POST
方法从Internet下载一些数据。 为此,我使用Messenger
。 这是我的代码,可以让您更加清楚:
我的onCreated()
方法:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_comments);
CommentsHandler commentsHandler = new CommentsHandler(this, savedInstanceState);
Messenger messenger = new Messenger(commentsHandler);
Intent serviceIntent = new Intent(this, WindowService.class);
serviceIntent.putExtra("messenger", messenger);
serviceIntent.putExtra("state", 888);
serviceIntent.putExtra("number", getIntent().getStringExtra("number"));
startService(serviceIntent);
}
我Service
线程中用于通过Messenger
对象将结果数据发布到Activity
的代码:
/** ... **/
Messenger messenger = intent.getParcelableExtra("messenger");
/** ... **/
Message resultMsg = this.obtainMessage();
resultMsg.obj = jParser.getArrayList(); //This is an ArrayList of my downloaded data.
messenger.send(resultMsg);
Activity
用于处理来自Service
的Message
的代码:
public static class CommentsHandler extends Handler {
Bundle mSavedInstanceState;
ActionBarActivity activity;
public CommentsHandler(Activity a, Bundle savedInstanceState) {
activity = (ActionBarActivity) a;
mSavedInstanceState = savedInstanceState;
}
@Override
public void handleMessage(Message msg) {
comments = (ArrayList<HashMap<String, String>>) msg.obj;
if (mSavedInstanceState == null && msg.arg1 != 793) {
activity.getSupportFragmentManager().beginTransaction()
.add(R.id.container, new CommentsFragment()).commit();
} else if (msg.arg1 == 793) { //793 is my preferred code to determine
//if the internet connection could not be
//established when the Service was trying
//to download the data.
activity.finish();
}
}
}
问题是:如果我在下载数据之前打开Activity
并关闭它,则此代码.add(R.id.container, new CommentsFragment()).commit();
给我一个错误, Can not perform this action after onSaveInstanceState
,因为仅在处理和通过Messenger
对象发送我的Service
的数据之后才执行此代码,但那时该Activity
已被用户关闭,因此无法对Fragment
进行操作。添加。 如何解决这个问题? 如何在添加Fragment
之前检查Activity
是否未关闭/正在关闭? 或者,更好的是,如何停止在Activity
的onDestroy()
方法上运行该代码的线程,以便在Activity
关闭时不执行该线程? 提前致谢!
在您的活动中,您应该创建一个布尔值以检查该活动是否可见:
public ActionBarActivity extends Activity {
private boolean isActivityVisible = false;
@Override
protected void onResume(){
isActivityVisible = true;
}
@Override
protected void onPause(){
isActivityVisible = false;
}
public boolean isVisible(){
return this.isActivityVisible;
}
}
然后修改您的Handler类定义:
public static class CommentsHandler extends Handler {
Bundle mSavedInstanceState;
ActionBarActivity activity;
public CommentsHandler(Activity a, Bundle savedInstanceState) {
activity = (ActionBarActivity) a;
mSavedInstanceState = savedInstanceState;
}
@Override
public void handleMessage(Message msg) {
// here you check if your activity is no longer visible and then break up
if(activity == null || !activity.isVisible())
return;
comments = (ArrayList<HashMap<String, String>>) msg.obj;
if (mSavedInstanceState == null && msg.arg1 != 793) {
activity.getSupportFragmentManager().beginTransaction()
.add(R.id.container, new CommentsFragment()).commit();
} else if (msg.arg1 == 793) { //793 is my preferred code to determine
//if the internet connection could not be
//established when the Service was trying
//to download the data.
activity.finish();
}
}
}
最小的更改是在Activity中具有一个布尔字段,在onResume()
中将其设置为true,在onPause()
handleMessage()
其设置为false,并在handleMessage()
检查其值(即,如果标志当前为false,则忽略消息) 。
另一种选择,而不是使用Messenger和handleMessage()
用做BroadcastReceiver
。 在onResume()
注册接收者,并在onPause()
注销它。 这样,来自该服务的广播将被简单地忽略。
无论如何,这两种解决方案基本相同,但是广播有些“更高级别”。
假设活动暂停,您对服务的结果不感兴趣。 如果您是(例如,如果您退出应用程序然后再返回,并且需要显示更新),则应该将接收到的数据放在一个字段中,并在随后的onResume()
。
您执行此操作的方式与我的处理方式不同,但是使用您拥有的内容,我将进行以下调整:
public static class CommentsHandler extends Handler {
Bundle mSavedInstanceState;
ActionBarActivity activity;
public CommentsHandler(Activity a, Bundle savedInstanceState) {
activity = (ActionBarActivity) a;
mSavedInstanceState = savedInstanceState;
}
public void setActivity(Activity a){
activity = a;
}
@Override
public void handleMessage(Message msg) {
if(activity == null){
return;
}
comments = (ArrayList<HashMap<String, String>>) msg.obj;
if (mSavedInstanceState == null && msg.arg1 != 793) {
activity.getSupportFragmentManager().beginTransaction()
.add(R.id.container, new CommentsFragment()).commit();
} else if (msg.arg1 == 793) { //793 is my preferred code to determine
//if the internet connection could not be
//established when the Service was trying
//to download the data.
activity.finish();
}
}
}
然后,我将使用您的活动onPause()/ onResume()方法来像这样:
@Override
protected void onPause() {
super.onPause();
commentsHandler.setActivity(null);
}
@Override
protected void onResume() {
super.onResume();
commentsHandler.setActivity(this);
}
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