android應(yīng)用程序,由一到多個Activity組成.每個Activity沒有很緊密的聯(lián)系,因?yàn)槲覀兛梢栽谧约旱某绦蛑姓{(diào)用其它Activity,特別是調(diào)用自己的代碼之外生成的Activity,比如android提供的發(fā)短信或者打電話的Activity.
Intent call = new Intent(Intent.ACTION_CALL,Uri.parse("tel:"+phonenumber);
startActivity(call);
Intent sms = new Intent(Intent.ACTION_SENDTO,Uri.parse("smsto:"+phonenumber);
startActivity(sms);
從這點(diǎn)上看,android應(yīng)用程序?qū)嶋H上是由多個Activity按照一定的次序拼裝起來的,只不過拼裝的過程中,后臺傳遞了一些數(shù)據(jù),使得各個Activity之間能比較好的銜接起來.
扯了這么多,其實(shí)我的意思還是想說,android應(yīng)用程序中,并沒有像c++和java這樣有main函數(shù)來作為應(yīng)用程序的入口.android應(yīng)用程序提供的是入口Activity,而非入口函數(shù).
在eclipse中創(chuàng)建一個android應(yīng)用程序的時候,默認(rèn)會創(chuàng)建一個Activity.這個Activity實(shí)際上就是入口Activity了.從哪里定義它是Activity呢?AndroidManifest.xml文件中定義了整個android應(yīng)用所包含的Activity.默認(rèn)生成的Activity的定義為:
<activity android:name=".activity01" android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
action節(jié)點(diǎn)中的android.intent.action.MAIN表明它所在的Activity是整個應(yīng)用程序的入口點(diǎn).而category中的android.intent.category.LAUNCHER意思是把這個Activityg歸屬到加載器類,即把這個Activity標(biāo)注為自動會加載和啟動的Activity,這樣程序啟動時候就先加載這個Activity了.參考手冊上是這么說的----"the LAUNCHER category says that this entry point should be listed in the application launcher."意思和我理解的有出入.不過意思都是說這個Activity要被應(yīng)用程序加載.
我們可以對比下eclipse中console端輸出的日志來看下.初始,我把 <category android:name="android.intent.category.LAUNCHER" />這一行在原先的xml文件中注釋掉了.可以看到控制臺會報錯"No Launcher activity found!",實(shí)際上此時在虛擬設(shè)備上的應(yīng)用程序列表中找不到"lifecycle_test"這個app,而且也沒法運(yùn)行,根本加載不起來.后面把注釋去掉,還原到最初始的狀態(tài),然后在啟動應(yīng)用,可以看到"No Launcher activity found!"這部分報錯信息沒有了,而且虛擬設(shè)備的屏幕上,可以看到"lifecycle_test"這個app已經(jīng)成功運(yùn)行了.
[2011-08-11 09:29:10 - lifecycle_test] ------------------------------
[2011-08-11 09:29:10 - lifecycle_test] Android Launch!
[2011-08-11 09:29:10 - lifecycle_test] adb is running normally.
[2011-08-11 09:29:10 - lifecycle_test] No Launcher activity found!
[2011-08-11 09:29:10 - lifecycle_test] The launch will only sync the application package on the device!
[2011-08-11 09:29:10 - lifecycle_test] Performing sync
[2011-08-11 09:29:10 - lifecycle_test] Automatic Target Mode: using existing emulator 'emulator-5554' running compatible AVD 'myavd_2.2'
[2011-08-11 09:29:15 - lifecycle_test] Application already deployed. No need to reinstall.
[2011-08-11 09:29:15 - lifecycle_test] \lifecycle_test\bin\lifecycle_test.apk installed on device
[2011-08-11 09:29:15 - lifecycle_test] Done!
[2011-08-11 09:30:47 - lifecycle_test] ------------------------------
[2011-08-11 09:30:47 - lifecycle_test] Android Launch!
[2011-08-11 09:30:47 - lifecycle_test] adb is running normally.
[2011-08-11 09:30:47 - lifecycle_test] Performing test.activity.leipei.activity01 activity launch
[2011-08-11 09:30:47 - lifecycle_test] Automatic Target Mode: using existing emulator 'emulator-5554' running compatible AVD 'myavd_2.2'
[2011-08-11 09:30:47 - lifecycle_test] Uploading lifecycle_test.apk onto device 'emulator-5554'
[2011-08-11 09:30:47 - lifecycle_test] Installing lifecycle_test.apk...
[2011-08-11 09:30:54 - lifecycle_test] Success!
[2011-08-11 09:30:55 - lifecycle_test] Starting activity test.activity.leipei.activity01 on device emulator-5554
[2011-08-11 09:30:57 - lifecycle_test] ActivityManager: Starting: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] cmp=test.activity.leipei/.activity01 }
