關於android應用程式的入口

    android應用程式,由一到多個Activity組成.每個Activity沒有很緊密的聯絡,因為我們可以在自己的程式中調用其它Activity,特別是調用自己的代碼之外產生的Activity,比如android提供的發簡訊或者打電話的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);
    從這點上看,android應用程式實際上是由多個Activity按照一定的次序拼裝起來的,只不過拼裝的過程中,後台傳遞了一些資料,使得各個Activity之間能比較好的銜接起來.
    扯了這麼多,其實我的意思還是想說,android應用程式中,並沒有像c++和java這樣有main函數來作為應用程式的入口.android應用程式提供的是入口Activity,而非入口函數.
    在eclipse中建立一個android應用程式的時候,預設會建立一個Activity.這個Activity實際上就是入口Activity了.從哪裡定義它是Activity呢?AndroidManifest.xml檔案中定義了整個android應用所包含的Activity.預設產生的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節點中的android.intent.action.MAIN表明它所在的Activity是整個應用程式的進入點.而category中的android.intent.category.LAUNCHER意思是把這個Activityg歸屬到載入器類,即把這個Activity標註為自動會載入和啟動的Activity,這樣程式啟動時候就先載入這個Activity了.參考手冊上是這麼說的----"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要被應用程式載入.
    我們可以對比下eclipse中console端輸出的日誌來看下.初始,我把    <category android:name="android.intent.category.LAUNCHER" />這一行在原先的xml檔案中注釋掉了.可以看到控制台會報錯"No Launcher activity found!",實際上此時在虛擬設備上的應用程式列表中找不到"lifecycle_test"這個app,而且也沒法運行,根本載入不起來.後面把注釋去掉,還原到最初始的狀態,然後在啟動應用,可以看到"No Launcher activity found!"這部分報錯資訊沒有了,而且虛擬設備的螢幕上,可以看到"lifecycle_test"這個app已經成功運行了.

[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 }