Android使用JetPack入门实例_Java

Android使用JetPack入门实例

概念

Android最流行框架-JetPack，采用MVVM的设计模式，数据流如下图所示。

程序实例

gradle添加依赖

androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
implementation "androidx.lifecycle:lifecycle-extensions:$lifecycle_version"

MainActivity.java

public class MainActivity extends AppCompatActivity {
    MyViewModel myViewModel;
    ActivityMainBinding binding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding= DataBindingUtil.setContentView(this, R.layout.activity_main);
        myViewModel= new ViewModelProvider(this).get(MyViewModel.class);
        binding.setData(myViewModel);
        binding.setLifecycleOwner(this);
        myViewModel.getLiveNum();
    }
}

MyViewModel.java

public class MyViewModel extends ViewModel {
    private MutableLiveData<Integer> liveNum;

    public MutableLiveData<Integer> getLiveNum() {
        if (liveNum==null) {
            liveNum=new MutableLiveData<>();
            liveNum.setValue(0);
        }
        return liveNum;
    }

    public void addLiveNum(int n) {
        liveNum.setValue(liveNum.getValue()+n);
    }
}

layout中使用viewModel

<?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">

    <data>
        <variable
            name="data"
            type="com.invensun.seven.ch34.MyViewModel" />

    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

        <TextView
            android:id="@+id/tvNum"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="100dp"
            android:text="@{String.valueOf(data.liveNum)}"
            android:textSize="24sp"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <Button
            android:id="@+id/btnAdd"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="50dp"
            android:text="+1"
            android:textSize="18sp"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.498"
            app:layout_constraintStart_toStartOf="parent"
            android:onClick="@{()->data.addLiveNum(1)}"
            app:layout_constraintTop_toBottomOf="@+id/tvNum" />

    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

本文地址：https://blog.csdn.net/quietbxj/article/details/108844543