Android系统横竖屏切换时候Activity的生命周期

网上看到有文章说横屏切换成竖屏的时候会打印两次相同的Log，百思不得其解啊，于是自己动手验证一下。

环境：
AndroidStudio 2.1.2
minSdkVersion 15 、targetSdkVersion 23
设备：Genymotion 4.1.1-API16

分为两个步骤：

• 不添加android:configChanges属性
• 添加android:configChanges=”orientation|screenSize”

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源代码

MainActivity.class

package com.example.activitydemo;import android.app.Activity;import android.content.res.Configuration;import android.os.Bundle;import android.util.Log;public class MainActivity extends Activity {    private String TAG = "MainActivity";    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        Log.i(TAG, "onCreate: ");    }    @Override    protected void onStart() {        super.onStart();        Log.i(TAG, "onStart: ");    }    @Override    protected void onResume() {        super.onResume();        Log.i(TAG, "onResume: ");    }    @Override    protected void onPause() {        super.onPause();        Log.i(TAG, "onPause: ");    }    @Override    protected void onStop() {        super.onStop();        Log.i(TAG, "onStop: ");    }    @Override    protected void onDestroy() {        super.onDestroy();        Log.i(TAG, "onDestroy: ");    }    @Override    protected void onRestart() {        super.onRestart();        Log.i(TAG, "onRestart: ");    }    @Override    protected void onSaveInstanceState(Bundle outState) {        super.onSaveInstanceState(outState);        Log.i(TAG, "onSaveInstanceState: ");    }    @Override    protected void onRestoreInstanceState(Bundle savedInstanceState) {        super.onRestoreInstanceState(savedInstanceState);        Log.i(TAG, "onRestoreInstanceState: ");    }    @Override    public void onConfigurationChanged(Configuration newConfig) {        super.onConfigurationChanged(newConfig);        Log.i(TAG, "onConfigurationChanged: ");    }}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="com.example.activitydemo">    <application        android:allowBackup="true"        android:icon="@mipmap/ic_launcher"        android:label="@string/app_name"        android:supportsRtl="true"        android:theme="@style/AppTheme">        <activity android:name=".MainActivity">            <intent-filter>                <action android:name="android.intent.action.MAIN" />                <category android:name="android.intent.category.LAUNCHER" />            </intent-filter>        </activity>    </application></manifest>

1.不添加android:configChanges属性:

创建Activity：

MainActivity: onCreate:

MainActivity: onStart:

MainActivity: onResume:

旋转至横屏：

MainActivity: onPause:

MainActivity: onSaveInstanceState:

MainActivity: onStop:

MainActivity: onDestroy:

MainActivity: onCreate:

MainActivity: onStart:

MainActivity: onRestoreInstanceState:

MainActivity: onResume:

旋转至竖屏：

MainActivity: onPause:

MainActivity: onSaveInstanceState:

MainActivity: onStop:

MainActivity: onDestroy:

MainActivity: onCreate:

MainActivity: onStart:

MainActivity: onRestoreInstanceState:

MainActivity: onResume:

再旋转至横屏：

MainActivity: onPause:

MainActivity: onSaveInstanceState:

MainActivity: onStop:

MainActivity: onDestroy:

MainActivity: onCreate:

MainActivity: onStart:

MainActivity: onRestoreInstanceState:

MainActivity: onResume:

小结：横竖屏切换Activity的生命周期跟预想的一样，只重启了一次。可以理解为先销毁竖屏的Activity，再创建横屏的Activity。网上说的打印两次Log的说法不知道是怎么来的。

2.添加android:configChanges属性:orientation|screenSize

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

ps: 若编译选项中的minSdkVersion和targetSdkVersion有一项大于13时，需同时添加orientation|screenSize属性才能防止旋转屏幕时Activity重启

创建Activity：

MainActivity: onCreate:

MainActivity: onStart:

MainActivity: onResume:

旋转至横屏：

MainActivity: onConfigurationChanged:

旋转至竖屏：

MainActivity: onConfigurationChanged:

小结：可以看到，添加了android:configChanges=”orientation|screenSize”属性的Activity在旋转屏幕时不会重启。