一個專案一般會自己先定義專案是橫屏還是豎屏但是也有可以橫屏和豎屏之間切換的activty。

切換橫豎屏的方法： 

//判斷當前螢幕方向
if(getRequestedOrientation() == ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE) {
    //切換豎屏
    MainActivity.this.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
}else{
    //切換橫屏
    MainActivity.this.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
}

　　

但是這樣切換橫豎屏會讓activity重新載入。生命週期為：

　　onStop
　　onDestroy
　　onCreate
　　onStart
　　onResume

為了解決這樣的問題在配置檔案里加上

android:configChanges="orientation|keyboardHidden|screenSize"

就不會重新載入頁面，只會進入到切換裡面的生命週期中。

　　onConfigurationChanged

AndroidManifest.xml

        <activity android:name=".MainActivity"
            android:configChanges="orientation|keyboardHidden|screenSize"
            >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

MainActivity.java　

package com.kkrs.change;

import android.content.pm.ActivityInfo;
import android.content.res.Configuration;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    private Button change;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        change = (Button)findViewById(R.id.change);
        Log.e("sys","onCreate");

    }

    @Override
    protected void onStart() {
        super.onStart();
        Log.e("sys","onStart");
        change.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Log.d("sys","被點選了");
                //判斷當前螢幕方向
                if(getRequestedOrientation() == ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE) {
                    //切換豎屏
                    MainActivity.this.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
                }else{
                    //切換橫屏
                    MainActivity.this.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
                }

            }
        });
    }

    //橫豎屏切換
    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        Log.e("sys","onConfigurationChanged");

    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.e("sys","onStop");

    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.e("sys","onResume");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.e("sys","onDestroy");

    }
}