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頁面畫完後，因為我們要資料綁定的關係，所以要對 Layout 做一些改變

安裝套件

implementation "androidx.lifecycle:lifecycle-extensions:2.2.0"
implementation "androidx.lifecycle:lifecycle-livedata-ktx:2.5.1"
implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:2.5.1"

建立 ViewModel

• 如果不需要 Context，可以繼承 ViewModel()

   class NoteViewModel: ViewModel() {     
       init {
           Log.d("maho", "ViewModel")
       }
  
       override fun onCleared() {
           super.onCleared()
           Log.d("maho", "NoteViewModel onCleared")
       }
   }
  

• 如果需要 Context，可以繼承 AndroidViewModel(application)，用getApplication<Application>()

  class NoteViewModel(application: Application): AndroidViewModel(application) {
      init {
          Log.d("maho", "NoteViewModel")
      }
  
      override fun onCleared() {
          super.onCleared()
          Log.d("maho", "NoteViewModel onCleared")
      }
  }
  

數據綁定相關

Gradle 啟動

android {
    buildFeatures {
        dataBinding true
    }
}

Layout 改寫

1. 把原本最上面和最下面的CoordinatorLayout改成layout
   • 原本

     <androidx.coordinatorlayout.widget.CoordinatorLayout
         xmlns:android="http://schemas.android.com/apk/res/android"
         xmlns:app="http://schemas.android.com/apk/res-auto"
         xmlns:tools="http://schemas.android.com/tools"
         android:layout_width="match_parent"
         android:layout_height="match_parent">
     
         ...
     
     </androidx.coordinatorlayout.widget.CoordinatorLayout>
     

   • 修改後

     <layout xmlns:android="http://schemas.android.com/apk/res/android"
         xmlns:app="http://schemas.android.com/apk/res-auto"
         xmlns:tools="http://schemas.android.com/tools">
     
         <androidx.coordinatorlayout.widget.CoordinatorLayout
             android:layout_width="match_parent"
             android:layout_height="match_parent">
     
             ...
     
         </androidx.coordinatorlayout.widget.CoordinatorLayout>
     </layout>
     

2. 增加<data>，然後增加剛剛新增的NoteViewModel

   <layout 
       xmlns:android="http://schemas.android.com/apk/res/android"
       xmlns:app="http://schemas.android.com/apk/res-auto"
       xmlns:tools="http://schemas.android.com/tools">
   
       <data>
   
           <variable
               name="NoteViewModel"
               type="com.example.hacknote.note.NoteViewModel" />
       </data>
   
   
       <androidx.coordinatorlayout.widget.CoordinatorLayout
           android:layout_width="match_parent"
           android:layout_height="match_parent">
   
           ...
   
       </androidx.coordinatorlayout.widget.CoordinatorLayout>
   </layout>