在活动的 onPause() 或 onStop() 状态运行代码

Question

There is a function in my android app that needs to run every time the user tries to edit his or her profile. There are two parts of edit profile in my app (please don't ask why, it has a very long tedious reason behind it). I need to revert back the changes the user did in the first part of the edit profile if the user decides to cancel everything. I have made a cancel button in the part two of edit profile but my question is, what if user presses the return button or the home button on the device and the app calls the onPause() and on onStop() ? how can I run the same code in these two phases of the activities? Anyone out there who knows how to put code in different states on activities? Do I just make a function onPause() and stick the code in there? Would that work?

Answer 1

Yes, it should definitely work. In your case, you should write your code in onPause() method.

Here is a summary of the Activity Lifecycle:

onCreate():

Called when the activity is first created. This is where you should do all of your normal static set up: create views, bind data to lists, etc. This method also provides you with a Bundle containing the activity's previously frozen state, if there was one. Always followed by onStart().

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //Write your code here
}

onStart():

Called when the activity is becoming visible to the user. Followed by onResume() if the activity comes to the foreground, or onStop() if it becomes hidden.

@Override
public void onStart() {
    super.onStart();
    //Write your code here
}

onResume():

Called when the activity will start interacting with the user. At this point your activity is at the top of the activity stack, with user input going to it. Always followed by onPause().

@Override
public void onResume() {
    super.onResume();
    //Write your code here
}

onPause():

Called when the system is about to start resuming a previous activity. This is typically used to commit unsaved changes to persistent data, stop animations and other things that may be consuming CPU, etc. Implementations of this method must be very quick because the next activity will not be resumed until this method returns. Followed by either onResume() if the activity returns back to the front, or onStop() if it becomes invisible to the user.

@Override
public void onPause() {
    super.onPause();
    //Write your code here
}

onStop():

Called when the activity is no longer visible to the user, because another activity has been resumed and is covering this one. This may happen either because a new activity is being started, an existing one is being brought in front of this one, or this one is being destroyed. Followed by either onRestart() if this activity is coming back to interact with the user, or onDestroy() if this activity is going away.

@Override
public void onStop() {
    super.onStop();
    //Write your code here
}

onDestroy():

The final call you receive before your activity is destroyed. This can happen either because the activity is finishing (someone called finish() on it, or because the system is temporarily destroying this instance of the activity to save space. You can distinguish between these two scenarios with the isFinishing() method.

@Override
public void onDestroy() {
    super.onDestroy();
    //Write your code here
}

Answer 2

You can do many things inside both onPause and onStop, just remember to call super.onPause(); , super.onStop(); or whatever you need inside each one, just follow the pattern below. Simply add the code to your Activity and you're good to go.

@Override
public void onPause() {
    super.onPause();  // Always call the superclass method first
    // Do what you want.
}

Additionaly, if you want your users to be able to go back on your activity and edit something instead of closing it, you can just call onBackPressed() :

@Override
public void onBackPressed() {
     super.onBackPressed();
     // You can just call onStop to close the app
     // or do what you want.
}

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Answer 3

只有 onPause 保证被调用