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;@Overrideprotected 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() {@Overridepublic void onClick(View v) {myviewModle.num++;textView.setText(String.valueOf(myviewModle.num));}});}
}