旋转屏幕重新加载Activity

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在启动一个acitivity之后，旋转一下屏幕（从竖屏模式切换到横屏模式，或者反过来）,尤其是带有侧滑键盘的机型打开滑动键盘时，如果屏幕为竖屏模式，则屏幕会被强制切换到横屏模式。当屏幕显示模式发生变化时，由于横竖屏显示模式存在一些明显的区别，Android系统会认为当前activity显示内容已经不再适合新的屏幕显示模式，所以它会重新加载当前的activity，选择合适的资源以适应新的屏幕显示模式。下面通过一个简单的例子跟踪Acitivity生命周期的变化。

新建一个工程，包含两个Activity分别为DemoParentActivity和DemoChildActivity，在第一个Activity中添加一个可以跳转到第二个Activity的按钮，并分别实现它们的生命周期函数，在函数里面打印一些日志信息，观察Activity生命周期函数调用情况。

ActivityTestActivity.class的代码：

01package com.devdiv.test.activitytest;02 03 04import android.app.Activity;05import android.content.Intent;06import android.content.res.Configuration;07import android.os.Bundle;08import android.util.Log;09import android.view.View;10 11public class ActivityTestActivity extends Activity {12    /** Called when the activity is first created. */13    @Override14    public void onCreate(Bundle savedInstanceState) {15        super.onCreate(savedInstanceState);16        setContentView(R.layout.main);17         18         19        if (savedInstanceState == null) {20                Log.d("test", "ActivityTestActivity - onCreate()");21                } else {22                        Log.d("test","ActivityTestActivity - onCreate() with a supplied savedInstanceState");23                }24    }25 26        @Override27        public void onConfigurationChanged(Configuration newConfig) {28                // TODO Auto-generated method stub29                super.onConfigurationChanged(newConfig);30                Log.d("test", "ActivityTestActivity - onConfigurationChanged()");31        }32 33        @Override34        protected void onDestroy() {35                // TODO Auto-generated method stub36                super.onDestroy();37                Log.d("test", "ActivityTestActivity - onDestroy()");38        }39 40        @Override41        protected void onPause() {42                // TODO Auto-generated method stub43                super.onPause();44                Log.d("test", "ActivityTestActivity - onPause()");45        }46 47        @Override48        protected void onRestart() {49                // TODO Auto-generated method stub50                super.onRestart();51                Log.d("test", "ActivityTestActivity - onRestart()");52        }53 54        @Override55        protected void onRestoreInstanceState(Bundle savedInstanceState) {56                // TODO Auto-generated method stub57                super.onRestoreInstanceState(savedInstanceState);58                Log.d("test", "ActivityTestActivity - onRestoreInstanceState()");59        }60 61        @Override62        protected void onResume() {63                // TODO Auto-generated method stub64                super.onResume();65                Log.d("test", "ActivityTestActivity - onResume()");66        }67 68        @Override69        protected void onSaveInstanceState(Bundle outState) {70                // TODO Auto-generated method stub71                super.onSaveInstanceState(outState);72                Log.d("test", "ActivityTestActivity - onSaveInstanceState()");73        }74 75        @Override76        protected void onStart() {77                // TODO Auto-generated method stub78                super.onStart();79                Log.d("test", "ActivityTestActivity - onStart()");80        }81 82        @Override83        protected void onStop() {84                // TODO Auto-generated method stub85                super.onStop();86                Log.d("test", "ActivityTestActivity - onStop()");87        }88         89        public void onButtonClick(View v) {90                Intent mIntent = new Intent(this, SecondActivity.class);91                startActivity(mIntent);92        }93     94     95}

SecondActivity.class的代码：

01package com.devdiv.test.activitytest;02 03 04import android.app.Activity;05import android.content.Intent;06import android.content.res.Configuration;07import android.os.Bundle;08import android.util.Log;09import android.view.View;10 11public class ActivityTestActivity extends Activity {12    /** Called when the activity is first created. */13    @Override14    public void onCreate(Bundle savedInstanceState) {15        super.onCreate(savedInstanceState);16        setContentView(R.layout.main);17         18         19        if (savedInstanceState == null) {20                Log.d("test", "ActivityTestActivity - onCreate()");21                } else {22                        Log.d("test","ActivityTestActivity - onCreate() with a supplied savedInstanceState");23                }24    }25 26        @Override27        public void onConfigurationChanged(Configuration newConfig) {28                // TODO Auto-generated method stub29                super.onConfigurationChanged(newConfig);30                Log.d("test", "ActivityTestActivity - onConfigurationChanged()");31        }32 33        @Override34        protected void onDestroy() {35                // TODO Auto-generated method stub36                super.onDestroy();37                Log.d("test", "ActivityTestActivity - onDestroy()");38        }39 40        @Override41        protected void onPause() {42                // TODO Auto-generated method stub43                super.onPause();44                Log.d("test", "ActivityTestActivity - onPause()");45        }46 47        @Override48        protected void onRestart() {49                // TODO Auto-generated method stub50                super.onRestart();51                Log.d("test", "ActivityTestActivity - onRestart()");52        }53 54        @Override55        protected void onRestoreInstanceState(Bundle savedInstanceState) {56                // TODO Auto-generated method stub57                super.onRestoreInstanceState(savedInstanceState);58                Log.d("test", "ActivityTestActivity - onRestoreInstanceState()");59        }60 61        @Override62        protected void onResume() {63                // TODO Auto-generated method stub64                super.onResume();65                Log.d("test", "ActivityTestActivity - onResume()");66        }67 68        @Override69        protected void onSaveInstanceState(Bundle outState) {70                // TODO Auto-generated method stub71                super.onSaveInstanceState(outState);72                Log.d("test", "ActivityTestActivity - onSaveInstanceState()");73        }74 75        @Override76        protected void onStart() {77                // TODO Auto-generated method stub78                super.onStart();79                Log.d("test", "ActivityTestActivity - onStart()");80        }81 82        @Override83        protected void onStop() {84                // TODO Auto-generated method stub85                super.onStop();86                Log.d("test", "ActivityTestActivity - onStop()");87        }88         89        public void onButtonClick(View v) {90                Intent mIntent = new Intent(this, SecondActivity.class);91                startActivity(mIntent);92        }93     94     95}        SecondActivity.class的代码：01package com.devdiv.test.activitytest;02 03import android.app.Activity;04import android.content.res.Configuration;05import android.os.Bundle;06import android.util.Log;07 08public class SecondActivity extends Activity {09         10        /** Called when the activity is first created. */11    @Override12    public void onCreate(Bundle savedInstanceState) {13        super.onCreate(savedInstanceState);14        setContentView(R.layout.second);15         16         17        if (savedInstanceState == null) {18                Log.d("test", "SecondActivity - onCreate()");19                } else {20                        Log.d("test","SecondActivity - onCreate() with a supplied savedInstanceState");21                }22    }23 24        @Override25        public void onConfigurationChanged(Configuration newConfig) {26                // TODO Auto-generated method stub27                super.onConfigurationChanged(newConfig);28                Log.d("test", "SecondActivity - onConfigurationChanged()");29        }30 31        @Override32        protected void onDestroy() {33                // TODO Auto-generated method stub34                super.onDestroy();35                Log.d("test", "SecondActivity - onDestroy()");36        }37 38        @Override39        protected void onPause() {40                // TODO Auto-generated method stub41                super.onPause();42                Log.d("test", "SecondActivity - onPause()");43        }44 45        @Override46        protected void onRestart() {47                // TODO Auto-generated method stub48                super.onRestart();49                Log.d("test", "SecondActivity - onRestart()");50        }51 52        @Override53        protected void onRestoreInstanceState(Bundle savedInstanceState) {54                // TODO Auto-generated method stub55                super.onRestoreInstanceState(savedInstanceState);56                Log.d("test", "SecondActivity - onRestoreInstanceState()");57        }58 59        @Override60        protected void onResume() {61                // TODO Auto-generated method stub62                super.onResume();63                Log.d("test", "SecondActivity - onResume()");64        }65 66        @Override67        protected void onSaveInstanceState(Bundle outState) {68                // TODO Auto-generated method stub69                super.onSaveInstanceState(outState);70                Log.d("test", "SecondActivity - onSaveInstanceState()");71        }72 73        @Override74        protected void onStart() {75                // TODO Auto-generated method stub76                super.onStart();77                Log.d("test", "SecondActivity - onStart()");78        }79 80        @Override81        protected void onStop() {82                // TODO Auto-generated method stub83                super.onStop();84                Log.d("test", "SecondActivity - onStop()");85        }86         87 88}

完成了工程代码之后，在eclipse中直接运行工程启动ActivityTestActivity，然后旋转手机（模拟器可以通过CTR+F11组合键进行横竖屏切换），可以从下图打印的日志中看到，当旋转手机屏幕后，DemoParentActivity被销毁后，又被重新加载了一次，同时还可以看到Activity的onSaveInstanceState和onRestoreInstanceState方法也被调用了，这就说明需要在切换屏幕显示模式时,通过这两个方法保存和恢复临时数据。

                                                        图1  模拟器LogCat日志信息
      某些情况下，并不希望在旋转屏幕时Activity被重新加载，这时可以通过修改Android应用工程的Androidmanifest.xml文件中Activity节点的android:configChanges属性，通常需要把这个属性设置为android:configChanges="orientation|navigation|keyboardHidden"，这表示当屏幕旋转，页面转换以及键盘隐藏时都不要重新加载Activity，而是调用onConfigurationChanged方法。在上面的代码中可以看到SecondActivity覆盖了Activity的onConfigurationChanged方法,并设置了activity的android:configChanges属性。

      接下来点击按钮来启动SecondActivity，然后旋转屏幕再看一下输出的日志信息，从图2-11中可以清楚的看到，当切换屏幕显示模式时，SecondActivity并没有被重新加载，只是调用了它的onConfigurationChanged()方法，如果并不希望在旋转屏幕时Activity被重新加载，那么需要实现Activity的onConfigurationChanged方法进行添加相应的的处理逻辑。

图2 模拟器LogCat日志信息

      旋转手机屏幕只会造成当前Activity的重新加载，并不会重新加载整个应用程序。现在有一个问题需要作进一步的分析，就是在旋转手机屏幕后，会不会影响Activity栈中其他的activity。在上面应用程序中，当旋转手机屏幕时，SecondActivity的onConfigurationChanged方法被调用，此时可以进行以下两种不同的操作：

      1、通过返回键，返回到ActivityTestActivity
      2、再次旋转屏幕之后，通过返回键，返回到ActivityTestActivity

      读者可以自行通过查看日志的方式验证，不再赘述。
      ActivityTest工程：DEMO