【記錄】Android中的Application
先定義一個(gè)Application
package com.xesam; import android.app.Application; import android.content.res.Configuration; import android.util.Log; public class ApplicationActivity extends Application { static String name = "小西山子"; @Override public void onCreate() { Log.v("ApplicationActivity","onCreate"); super.onCreate(); } @Override public void onTerminate() { Log.v("ApplicationActivity","onTerminate"); super.onTerminate(); } @Override public void onConfigurationChanged(Configuration newConfig) { Log.v("ApplicationActivity","onConfigurationChanged"); super.onConfigurationChanged(newConfig); } @Override public void onLowMemory() { Log.v("ApplicationActivity","onLowMemory"); super.onLowMemory(); } }
主要Activity：
package com.xesam; import android.app.Activity; import android.graphics.Color; import android.os.Bundle; import android.util.Log; import android.view.ViewGroup.LayoutParams; import android.widget.LinearLayout; import android.widget.TextView; public class MainActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { Log.v("MainActivity","onCreate"); super.onCreate(savedInstanceState); ApplicationActivity app = (ApplicationActivity)this.getApplication(); LinearLayout main = new LinearLayout(this); main.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT,LayoutParams.FILL_PARENT)); main.setOrientation(LinearLayout.VERTICAL); TextView tv = new TextView(this); tv.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT,LayoutParams.FILL_PARENT)); tv.setText(app.name); tv.setTextColor(Color.BLUE); main.addView(tv); setContentView(main); } @Override public void onDestroy(){ Log.v("MainActivity","onDestroy"); super.onDestroy(); //System.exit(0); } }
AndroidManifest.xml：
<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.xesam" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="8" /> <application android:icon="@drawable/ic_launcher" android:label="@string/app_name" android:name="ApplicationActivity"> <activity android:name=".MainActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> </manifest>
這里我們自定義了一個(gè)Application，所以必須指定AndroidManifest.xml中application的android:name屬性（默認(rèn)是android.app.Application）。
輸出結(jié)果：
"ApplicationActivity","onCreate" "MainActivity","onCreate" "MainActivity","小西山子" "ApplicationActivity","onConfigurationChanged"
退出之后打印結(jié)果：
"MainActivity","onDestroy"
從模擬器再次開啟應(yīng)用（沒有再次編譯）之后，打印結(jié)果
"MainActivity","onCreate" "MainActivity","小西山子"
所以后退的時(shí)候并沒有關(guān)閉application，要強(qiáng)制關(guān)閉application，可以在MainActivity的onDestroy中調(diào)用System.exit(0)
@Override public void onDestroy(){ Log.v("MainActivity","onDestroy"); super.onDestroy(); System.exit(0); }
這樣就完全退出程序了。
回到application的問題上來，顯然，application的onCreate在activity的onCreate之前執(zhí)行了，所以整個(gè)應(yīng)用的最初入口是這個(gè)方法。
onCreate作用說明：
/** * Called when the application is starting, before any other application * objects have been created. Implementations should be as quick as * possible (for example using lazy initialization of state) since the time * spent in this function directly impacts the performance of starting the * first activity, service, or receiver in a process. * If you override this method, be sure to call super.onCreate(). */
可以認(rèn)為Activity，service以及其他的組件共同構(gòu)成了一個(gè)application的環(huán)境，因此application中可以共享或者初始化一些全局變量，比如地圖（百度地圖demo就是這么做的）。
注：eclipse查看源碼的方法：
下載android版本對(duì)應(yīng)的源碼【2.2版本地址：http://rgruet.free.fr/public/android-2.2-froyo-src.zip】
解壓縮到 /usr/local/android-sdk-linux/platforms/android-8下，然后修改同目錄下source.properties文件中的Pkg.SourceUrl為剛才解壓的源碼目錄就行了
一個(gè)示例（我下載的源碼放在/usr/local/android-sdk-linux/platforms/android-8/source目錄中，所以Pkg.SourceUrl=sources）：
### Android Tool: Source of this archive. #Mon Apr 23 01:14:48 CST 2012 Layoutlib.Api=4 Layoutlib.Revision=0 Pkg.Desc=Android SDK Platform 2.2_r3 Archive.Arch=ANY Platform.Version=2.2 Pkg.DescUrl=http\://developer.android.com/sdk/ Platform.MinToolsRev=8 Archive.Os=ANY Pkg.SourceUrl=sources Pkg.Revision=3 AndroidVersion.ApiLevel=8
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