Activity lifecycle

Activity Life cycle

One 、 Life cycle diagram

Two 、 The callback method

1. onCteate()： When Activity When it was first created , Will execute this method . Generally, some initialization will be done , Input the binding of events .
2. onStart()： When Activity When displayed to the user , Will execute this method . At this point, the user can see this Activity, But no interaction , It can be simply understood as seeing , Unable to touch .
3. onResume()： When Activity At the front desk , Will execute this method . At this point, the user can contact the Activity Interact , And at this time Activity Stack top . That is, you can see and touch it .
4. onPause()： When there is another Activity Overwrite current Activity when , Will execute this method . Previous Activity Will lose focus and save data , And it's visible , Just can't interact with users .
5. onStop()： When Activity It's not visible , Will execute onStop(), At this moment Activity Will run in the background , It's not going to be destroyed .
6. onDestroy()： When you click the return key on the system interface , Will execute Activity Of finish() Method , At this time Activity Will be destroyed .
7. onRestart()： When the second Activity After being destroyed , first Activity Will return to the front desk , This method will be executed . But Scene 2 corresponds to FirstActivity This method will not be executed , Because it is displayed in the form of pop-up SecondActivity, Not completely covered FirstActivity, therefore FirstActivity No implementation onStop(), It won't execute onRestart() The method , The principle can refer to the above life cycle diagram .

3、 ... and 、 Examples demonstrate

Two are used here Activity give an example ：FirstActivity、SecondActivity. Rewrite all life cycle methods , Print log .

Scene one ：SecondActivity Adopted and FirstActivity The same default full screen display .

1. When to start FirstActivity when , Will execute FirstActivity Of onCteate()、onStart()、onResume() Method . as follows ：

2. Click on FirstActivity The first button in , Jump to SecondActivity, here FirstActivity Will execute onPause()、onStop() Method , Thus invisible . and SecondActivity Will be created , perform onCteate()、onStart()、onResume() Method . as follows ：

3. Click the phone return button , Equivalent to execution Activity Of finish() Method . here SecondActivity Will be destroyed , Will execute onPause()、onStop()、onDestroy() Method . and FirstActivity Will return to the front desk , Will execute onRestart()、onStart()、onResume() Method . as follows ：

4. Click back again ,FirstActivity It's going to be destroyed , One after another onPause()、onStop()、onDestroy() Method .

Scene two ：SecondActivity Display in the form of pop-up window .

1. When to start FirstActivity when , Will execute FirstActivity Of onCteate()、onStart()、onResume() Method . as follows ：

2. Click on FirstActivity The first button in , Jump to SecondActivity, here FirstActivity Only execute onPause() Method , It's partially visible . and SecondActivity Will be created , perform onCteate()、onStart()、onResume() Method . as follows ：

3. Click the phone return button , Equivalent to execution Activity Of finish() Method . here SecondActivity Will be destroyed , Will execute onPause()、onStop()、onDestroy() Method . and FirstActivity Will be Partially visible To All visible , Only execute onResume() Method . as follows ：

4. Click back again ,FirstActivity It's going to be destroyed , One after another onPause()、onStop()、onDestroy() Method . as follows ：