Andriod --- JetPack (五)：DataBinding + LiveData +ViewModel 简单实例

1.Andriod — JetPack (一)：初识 JetPack

2.Andriod — JetPack (二)：LifeCycle 的诞生

3.Andriod — JetPack (三)：ViewModel 的诞生

4.Andriod — JetPack (四)：BaseObservable 与 ObservableField 双向绑定

5.Andriod — JetPack (五)：DataBinding + LiveData +ViewModel 简单实例

6.Andriod — JetPack (六)：Room 增删改查

7.Andriod — JetPack (七)：Room + ViewModel + LiveData 增删改查实例

一、DataBinding

1.让布局页面承担了部分原本属于页面的工作，是页面文件和布局耦合度进一步降低。页面文件：Activity。布局：activity_main.xml

2.减少了很多 findViewById 与 OnClickListener
布局文件可以包含一些简单的业务逻辑

二、LiveData

在 ViewModel 中的数据发生变化时通知页面
LiveData 与 ObservableField 同样可以实现双向绑定
这里的 Model 层下面的例子未呈现，等过后学到了 JetPack - Room 自然就懂了

三、ViewModel

1.它是介于 View（视图）和 Model（数据模型）直接的桥梁
2.使视图和数据能够分离，也能够保持通信
https://blog.csdn.net/qq_43290288/article/details/123478346

四：DataBinding + LiveData +ViewModel 实例

在 build.gradle 中添加 DataBinding 支持

android {dataBinding {enabled = true}
}

自定义MyViewModel.java

import android.view.View;import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;public class MyViewModel extends ViewModel {private MutableLiveData<Integer> aTeamScore;private MutableLiveData<Integer> bTeamScore;public MutableLiveData<Integer> getaTeamScore() {if(aTeamScore == null) {aTeamScore = new MutableLiveData<>();aTeamScore.setValue(0);}return aTeamScore;}public MutableLiveData<Integer> getbTeamScore() {if(bTeamScore == null) {bTeamScore = new MutableLiveData<>();bTeamScore.setValue(0);}return bTeamScore;}public void aTeamAdd(View view) {aTeamScore.setValue(aTeamScore.getValue() + 1);}public void bTeamAdd() {bTeamScore.setValue(bTeamScore.getValue() + 1);}
}

MainActivity.java

import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import androidx.lifecycle.ViewModel;
import androidx.lifecycle.ViewModelProvider;import android.database.DatabaseUtils;
import android.os.Bundle;import com.example.mvvm20220312.databinding.ActivityMainBinding;
import com.example.mvvm20220312.viewmodel.MyViewModel;public class MainActivity extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_main); // ActivityMainBinding 对应 activity_main.xmlMyViewModel viewModel  = new ViewModelProvider(this, new ViewModelProvider.AndroidViewModelFactory(getApplication())).get(MyViewModel.class);binding.setViewModel(viewModel); // DataBinding 与 ViewModel 绑定binding.setLifecycleOwner(this); // 要想在绑定类中使用 LiveData 对象，我们需要指定生命周期所有者来定义 LiveData 对象的范围。在绑定类实例化后指定 activity 作为生命周期所有者}}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<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"tools:context=".MainActivity"><data><variablename="viewModel"type="com.example.mvvm20220312.viewmodel.MyViewModel" /></data><androidx.constraintlayout.widget.ConstraintLayoutandroid:layout_width="match_parent"android:layout_height="match_parent"><TextViewandroid:id="@+id/textView2"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="@{String.valueOf(viewModel.getaTeamScore())}"android:textSize="36sp"tools:text="10"app:layout_constraintBottom_toBottomOf="parent"app:layout_constraintEnd_toEndOf="parent"app:layout_constraintHorizontal_bias="0.252"app:layout_constraintStart_toStartOf="parent"app:layout_constraintTop_toTopOf="parent"app:layout_constraintVertical_bias="0.174" /><TextViewandroid:id="@+id/textView3"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="@{String.valueOf(viewModel.getbTeamScore())}"android:textSize="36sp"tools:text="10"app:layout_constraintBottom_toBottomOf="parent"app:layout_constraintEnd_toEndOf="parent"app:layout_constraintHorizontal_bias="0.588"app:layout_constraintStart_toEndOf="@+id/textView2"app:layout_constraintTop_toTopOf="parent"app:layout_constraintVertical_bias="0.174" /><Buttonandroid:id="@+id/button"android:layout_width="wrap_content"android:layout_height="wrap_content"app:layout_constraintBottom_toBottomOf="parent"app:layout_constraintEnd_toEndOf="parent"app:layout_constraintHorizontal_bias="0.207"android:onClick="@{viewModel::aTeamAdd}"app:layout_constraintStart_toStartOf="parent"app:layout_constraintTop_toBottomOf="@+id/textView2"android:text="蓝队"app:layout_constraintVertical_bias="0.499" /><Buttonandroid:id="@+id/button2"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="红队"android:onClick="@{() -> viewModel.bTeamAdd()}"app:layout_constraintBottom_toBottomOf="parent"app:layout_constraintEnd_toEndOf="parent"app:layout_constraintHorizontal_bias="0.755"app:layout_constraintStart_toStartOf="parent"app:layout_constraintTop_toBottomOf="@+id/textView3"app:layout_constraintVertical_bias="0.499" /></androidx.constraintlayout.widget.ConstraintLayout>
</layout>

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