有些時候,應用需要在開機時就自動運行,例如某個自動從網上更新內容的後台service。怎樣實現開機自動啟動並執行應用?在撰寫本文時,聯想到高煥堂先生以“Don't call me, I'll call you back!”總結Android架構,真是說到點子上了。理解這句話的含義,許多有關Android平台上實現某種功能的問題,都能迎刃而解。
使用情境:手機開機後,自動運行程式,在螢幕上顯示"Hello. I started!"字樣。
背景知識:當Android啟動時,會發出一個系統廣播,內容為ACTION_BOOT_COMPLETED,它的字串常量表示為android.intent.action.BOOT_COMPLETED。只要在程式中“捕捉”到這個訊息,再啟動之即可。記住,Android架構說:Don't call me, I'll call you back。我們要做的是做好接收這個訊息的準備,而實現的手段就是實現一個BroadcastReceiver。
代碼解析:
1、介面Activity:SayHello.java
[java] view plaincopyprint?
- package com.ghstudio.BootStartDemo;
-
- import android.app.Activity;
- import android.os.Bundle;
- import android.widget.TextView;
-
- public class SayHello extends Activity {
-
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
-
-
- TextView tv = new TextView(this);
- tv.setText("Hello. I started!");
-
-
- setContentView(tv);
- }
- }
package com.ghstudio.BootStartDemo;</p><p>import android.app.Activity;<br />import android.os.Bundle;<br />import android.widget.TextView;</p><p>public class SayHello extends Activity {</p><p> @Override<br /> public void onCreate(Bundle savedInstanceState) {<br /> super.onCreate(savedInstanceState);</p><p> TextView tv = new TextView(this);<br /> tv.setText("Hello. I started!");</p><p> setContentView(tv);<br /> }<br />}</p><p>
這段代碼很簡單,當Activity啟動時,建立一個TextView,用它顯示"Hello. I started!"字樣。
2、接收廣播訊息:BootBroadcastReceiver.java
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- package com.ghstudio.BootStartDemo;
-
- import android.content.BroadcastReceiver;
- import android.content.Context;
- import android.content.Intent;
-
- public class BootBroadcastReceiver extends BroadcastReceiver {
-
- static final String ACTION = "android.intent.action.BOOT_COMPLETED";
-
- @Override
- public void onReceive(Context context, Intent intent) {
-
- if (intent.getAction().equals(ACTION)){
- Intent sayHelloIntent=new Intent(context,SayHello.class);
- sayHelloIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
-
- context.startActivity(sayHelloIntent);
- }
- }
-
- }
package com.ghstudio.BootStartDemo;</p><p>import android.content.BroadcastReceiver;<br />import android.content.Context;<br />import android.content.Intent;</p><p>public class BootBroadcastReceiver extends BroadcastReceiver {</p><p> static final String ACTION = "android.intent.action.BOOT_COMPLETED";</p><p> @Override<br /> public void onReceive(Context context, Intent intent) {</p><p> if (intent.getAction().equals(ACTION)){<br /> Intent sayHelloIntent=new Intent(context,SayHello.class);<br /> sayHelloIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);</p><p> context.startActivity(sayHelloIntent);<br /> }<br /> }</p><p>}</p><p>
該類派生自BroadcastReceiver,覆載方法onReceive中,檢測接收到的Intent是否符合BOOT_COMPLETED,如果符合,則啟動SayHello那個Activity。
3、設定檔:AndroidManifest.xml
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- <?xml version="1.0" encoding="utf-8"?>
- <manifest xmlns:android="http://schemas.android.com/apk/res/android"
- package="com.ghstudio.BootStartDemo"
- android:versionCode="1"
- android:versionName="1.0">
- <application android:icon="@drawable/icon" android:label="@string/app_name">
- <activity android:name=".SayHello"
- android:label="@string/app_name">
- <intent-filter>
- <action android:name="android.intent.action.MAIN" />
- <category android:name="android.intent.category.LAUNCHER" />
- </intent-filter>
- </activity>
- <receiver android:name=".BootBroadcastReceiver">
- <intent-filter>
- <action android:name="android.intent.action.BOOT_COMPLETED" />
- </intent-filter>
- </receiver>
- </application>
- <uses-sdk android:minSdkVersion="3" />
-
- <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"></uses-permission>
-
- </manifest>
<?xml version="1.0" encoding="utf-8"?><br /><manifest xmlns:android="http://schemas.android.com/apk/res/android"<br /> package="com.ghstudio.BootStartDemo"<br /> android:versionCode="1"<br /> android:versionName="1.0"><br /> <application android:icon="@drawable/icon" android:label="@string/app_name"><br /> <activity android:name=".SayHello"<br /> android:label="@string/app_name"><br /> <intent-filter><br /> <action android:name="android.intent.action.MAIN" /><br /> <category android:name="android.intent.category.LAUNCHER" /><br /> </intent-filter><br /> </activity><br /> <receiver android:name=".BootBroadcastReceiver"><br /> <intent-filter><br /> <action android:name="android.intent.action.BOOT_COMPLETED" /><br /> </intent-filter><br /> </receiver><br /> </application><br /> <uses-sdk android:minSdkVersion="3" /></p><p> <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"></uses-permission></p><p></manifest><br />
注意其中粗體字那一部分,該節點向系統註冊了一個receiver,子節點intent-filter表示接收android.intent.action.BOOT_COMPLETED訊息。不要忘記配置android.permission.RECEIVE_BOOT_COMPLETED許可權。
完成後,編譯出apk包,安裝到模擬器或手機中。關機,重新開機。
運行:
延伸思考:在多數情況下,要自動啟動並執行不是有介面的程式,而是在後台啟動並執行service。此時,就要用startService來啟動相應的service了。