AndroidJetpack组件之ViewModel使用详解

<?xml version="1.0" encoding="utf-8"?>
<Androidx.constraintlayout.widget.ConstraintLayout 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"
    tools:context=".MainActivity">
    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="0"
        android:textSize="24sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.247" />
    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="+"
        android:textSize="34sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:onClick="plusNumber"/>
</androidx.constraintlayout.widget.ConstraintLayout>

package com.example.viewmodel;
import androidx.lifecycle.ViewModel;
public class MyViewModel extends ViewModel {
    public int number;
}

package com.example.viewmodel;
import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.ViewModelProvider;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
    private TextView textView;
    private MyViewModel viewModel;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView = findViewById(R.id.textView);
        // 获取到 MyViewModel
        viewModel = new ViewModelProvider(this,
                new ViewModelProvider.AndroidViewModelFactory(getApplication())).get(MyViewModel.class);
        textView.setText(String.valueOf(viewModel.number));
    }
    
    public void plusNumber(View view) {
        textView.setText(String.valueOf(++viewModel.number));
    }
}

public class MyViewModel extends AndroidViewModel