Android Studio 屏幕方向以及UI界面状态的保存

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"）
      <activity android:name=".MainActivity" 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());
    }
}
　　项目：Orientation

　　

【创建横屏】

1.禁止切换横屏：在 AndroidManifest.xml-->application->activity->中设置如下代码（android:screenOrientation="portrait"）
      <activity android:name=".MainActivity" 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;

注意：这里屏幕翻转后，会导致界面重新加载，界面上原来计算的数值就会重新变成初始状态。
所以为了解决这个问题，可以用 onSaveInstanceState 这个事件来保存控件状态
@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());
    }

然后在界面 onCreate()的时候，如果这个值如果已经存在了，就自动加载出来
//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);
 }