AndroidStudio屏幕方向以及UI界面状态的保存代码详解

package com.example.orientation;
 
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
 
import androidx.appcompat.app.AppCompatActivity;
 
public class MainActivity extends AppCompatActivity {
/*
  = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
  本实例主要学习，屏幕翻转时，界面如何自适应，创建横屏布局
  1.禁止切换横屏：在 AndroidManifest.xml-->application->activity->中设置如下代码（android:screenOrientation="portrait"）
   
  2. 创建 Landscape 布局，横屏时，会自动加载 Landscape 的布局界面（清单文件中，注意去掉 android:screenOrientation="portrait" ）
  3. 翻转屏幕时，保存窗口控件的状态值;
 
  = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
 */
  Button button;
  TextView textView;
 
  String TAG = "myTag";
 
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
 
    button = findViewById(R.id.button );
    textView = findViewById(R.id.textView);
 
    //如果State中的值不为空，如果有相应的这个组件的值，则读取出来赋值上去
    if(savedInstanceState !=null)
    {
      String s = savedInstanceState.getString("key");
      textView.setText(s);
    }
 
    button.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View view) {
        textView.setText(button.getText());
      }
    });
  }
 
  @Override
  protected void onDestroy() {
    super.onDestroy();
    Log.d(TAG,"onDestroy:");
  }
 
  @Override
  //将 textView 中的值，先保存到 outState 中（键值对）
  public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putString("key",textView.getText().toString());
  }
}