2.A Service is not a thread. It is not a means itself to do work off of the main thread (to avoid Application Not Responding errors).
稍微翻一下
1.Service不是一個單獨的進程 ,它和應用程序在同一個進程中。
2.Service不是一個線程,所以我們應該避免在Service裏面進行耗時的操作
關於第二點我想說下,不知道很多網上的文章都把耗時的操作直接放在Service的onStart方法中,而且沒有強調這樣會出現Application Not Responding!希望我的文章能幫大家認清這個誤區(Service不是一個線程,不能直接處理耗時的操作)。
有人肯定會問,那麼爲什麼我不直接用Thread而要用Service呢?關於這個,大家可以網上搜搜,這裏不過多解釋。有一點需要強調,如果有耗時操作在Service裏,就必須開啓一個單獨的線程來處理!!!這點一定要銘記在心。
IntentService相對於Service來說,有幾個非常有用的優點,首先我們看看官方文檔的說明:
IntentService is a base class for Services that handle asynchronous requests (expressed as Intents) on demand. Clients send requests throughstartService(Intent) calls; the service is started as needed, handles each Intent
in turn using a worker thread, and stops itself when it runs out of work.
This "work queue processor" pattern is commonly used to offload tasks from an application's main thread. The IntentService class exists to simplify this pattern and take care of the mechanics. To use it, extend IntentService
and implement onHandleIntent(Intent). IntentService will receive the Intents, launch a worker thread, and stop the service as appropriate.
All requests are handled on a single worker thread -- they may take as long as necessary (and will not block the application's main loop), but only one request will be processed at a time.
All requests are handled on a single worker thread -- they may take as long as necessary (and will not block the application's main loop), but only one request will be processed at a time.
稍微翻譯理一理,這裏主要是說IntentService使用隊列的方式將請求的Intent加入隊列,然後開啓一個worker thread(線程)來處理隊列中的Intent,對於異步的startService請求,IntentService會處理完成一個之後再處理第二個,每一個請求都會在一個單獨的worker thread中處理,不會阻塞應用程序的主線程,這裏就給我們提供了一個思路,如果有耗時的操作與其在Service裏面開啓新線程還不如使用IntentService來處理耗時操作。下面給一個小例子:
1.Service:
package com.zhf.service;
import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
public class MyService extends Service {
@Override
public void onCreate() {
super.onCreate();
}
@Override
public void onStart(Intent intent, int startId) {
super.onStart(intent, startId);
//經測試,Service裏面是不能進行耗時的操作的,必須要手動開啓一個工作線程來處理耗時操作
System.out.println("onStart");
try {
Thread.sleep(20000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("睡眠結束");
}
@Override
public IBinder onBind(Intent intent) {
return null;
}
}
2.IntentService:
package com.zhf.service;
import android.app.IntentService;
import android.content.Intent;
public class MyIntentService extends IntentService {
public MyIntentService() {
super("yyyyyyyyyyy");
}
@Override
protected void onHandleIntent(Intent intent) {
// 經測試,IntentService裏面是可以進行耗時的操作的
//IntentService使用隊列的方式將請求的Intent加入隊列,然後開啓一個worker thread(線程)來處理隊列中的Intent
//對於異步的startService請求,IntentService會處理完成一個之後再處理第二個
System.out.println("onStart");
try {
Thread.sleep(20000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("睡眠結束");
}
}
測試主程序:package com.zhf.service;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
public class ServiceDemoActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
startService(new Intent(this,MyService.class));//主界面阻塞,最終會出現Application not responding
//連續兩次啓動IntentService,會發現應用程序不會阻塞,而且最重的是第二次的請求會再第一個請求結束之後運行(這個證實了IntentService採用單獨的線程每次只從隊列中拿出一個請求進行處理)
startService(new Intent(this,MyIntentService.class));
startService(new Intent(this,MyIntentService.class));
}
}