Android ： ViewModel_解决textView 横竖屏数据丢失

横竖屏切换  textView  数据丢失
1.导包  
// 使用androidx版本库
    implementation 'androidx.lifecycle:lifecycle-extensions:2.1.0-alpha03'
     // 或者，使用support版本库
    implementation 'android.arch.lifecycle:extensions:1.1.1'

2.写个类 继承 viewModel
import androidx.lifecycle.ViewModel;

public class MyviewModel extends ViewModel {
public int num =0;
}

3.
package com.example.myviewmodle;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.ViewModelProviders;

public class MainActivity extends AppCompatActivity {
private Button button;
private TextView textView;

private MyviewModel myviewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

myviewModel= ViewModelProviders.of(this).get(MyviewModel.class);

button = findViewById(R.id.button);
textView = findViewById(R.id.textView);

//从新创建时获取一遍值
textView.setText(String.valueOf(myviewModel.num));

button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
myviewModle.num++;
textView.setText(String.valueOf(myviewModle.num));
}
});
}
}

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