• The onCreate() method is where you should do any one-time initializations for your activity. For example, in onCreate(), you call setContent(), which specifies the activity's UI layout.

  <aside> 💡 Note: When you override the onCreate() method, you must call the superclass implementation to complete the creation of the Activity, so within it, you must immediately call super.onCreate(). The same is true for other lifecycle callback methods.

  </aside>

• how configuration changes affect the lifecycle of your activities：onDestroy(), which is called after onStop() → FOR MORE , USING DATA LAYER.

  • Lifecycle of a composable: Composable functions have their own lifecycle that is independent of the Activity lifecycle. Its lifecycle is composed of the events: enters the Composition, recomposing 0 or more times, and then leaving the Composition.
    • var revenue = mutableStateOf(0)to have Compose trigger a recomposition when the revenue value changes
    • var revenue by remember { mutableStateOf(0) }To instruct Compose to retain and reuse its value during recompositions
    • to retain the state during a configuration change

使用技巧

• Override/Implement Members 使用快捷键ctrl+字母O ，或者 with MainActivity.kt open and the cursor within the MainActivity class, select Code > Override Methods

LogCat

There are three important aspects of the Log instruction:

• The priority of the log message, that is, how important the message is. In this case, the Log.v() logs verbose messages. Log.d() method writes a debug message. Other methods in the Log class include Log.i() for informational messages, Log.w() for warnings, and Log.e() for error messages.

• The log tag (the first parameter), in this case "MainActivity". The tag is a string that lets you more easily find your log messages in the Logcat. The tag is typically the name of the class.

• The actual log message, called msg (the second parameter), is a short string, which in this case is "onCreate Called".