PendingIntent是一個(gè)Intent的描述、包裝，給予了這個(gè)PendingIntent 的組件在指定的事件發(fā)生或指定的時(shí)間到達(dá)時(shí)啟動(dòng)Activty、Service或者Broadcast。

根據(jù)是要啟動(dòng)Activity、Service還是Broadcast分別對(duì)應(yīng)一個(gè)獲取PendingIntent的方法

public static PendingIntent getActivity(Context context, int requestCode,
            Intent intent, int flags)

public static PendingIntent getBroadcast(Context context, int requestCode
            Intent intent, int flags)

public static PendingIntent getService(Context context, int requestCode,
            Intent intent, int flags)


三個(gè)函數(shù)的參數(shù)都相同，其中最后一個(gè)參數(shù)flags在文檔中是這樣解析的：


flags：  May be FLAG_ONE_SHOT,LAG_NO_CREATE,LAG_CANCEL_CURRENT, FLAG_UPDATE_CURRENT, or any of the flags as  supported by Intent.fillIn() to control which unspecified parts of the intent that can be supplied when the actual send happens.

目前為止只提供FLAG_ONE_SHOT, FLAG_NO_CREATE, FLAG_CANCEL_CURRENT, FLAG_UPDATE_CURRENT這四個(gè)flag


FLAG_ONE_SHOT:this PendingIntent can only be used once. If set, after send() is called on it, it will be automatically canceled for you and any future attempt to send through it will fail.
利用 FLAG_ONE_SHOT獲取的PendingIntent只能使用一次，即使再次利用上面三個(gè)方法重新獲取，再使用PendingIntent也將失敗。


FLAG_NO_CREATE:if the described PendingIntent does not already exist, then simply return null instead of creating it.
利用FLAG_NO_CREAT獲取的PendingIntent，若描述的Intent不存在則返回NULL值.


FLAG_CANCEL_CURRENT:if the described PendingIntent already exists, the current one is canceled before generating a new one. You can use this to retrieve a new PendingIntent when you are only changing the extra data in the Intent; by canceling the previous pending intent, this ensures that only entities given the new data will be able to launch it. If this assurance is not an issue, consider FLAG_UPDATE_CURRENT.
如果描述的PendingIntent已經(jīng)存在，則在產(chǎn)生新的Intent之前會(huì)先取消掉當(dāng)前的。你可用使用它去檢索新的Intent，如果你只是想改變Intent中的額外數(shù)據(jù)的話。通過取消先前的Intent，可用確保只有最新的實(shí)體可用啟動(dòng)它。如果這一保證不是問題，考慮flag_update_current。



FLAG_UPDATE_CURRENT: if the described PendingIntent already exists, then keep it but its replace its extra data with what is in this new Intent. This can be used if you are creating intents where only the extras change, and don't care that any entities that received your previous PendingIntent will be able to launch it with your new extras even if they are not explicitly given to it.
最經(jīng)常使用的是FLAG_UPDATE_CURRENT，因?yàn)槊枋龅腎ntent有 更新的時(shí)候需要用到這個(gè)flag去更新你的描述，否則組件在下次事件發(fā)生或時(shí)間到達(dá)的時(shí)候extras永遠(yuǎn)是第一次Intent的extras。


上面4個(gè)flag中最經(jīng)常使用的是FLAG_UPDATE_CURRENT，因?yàn)槊枋龅腎ntent有 更新的時(shí)候需要用到這個(gè)flag去更新你的描述，否則組件在下次事件發(fā)生或時(shí)間到達(dá)的時(shí)候extras永遠(yuǎn)是第一次Intent的extras。
使用 FLAG_CANCEL_CURRENT也能做到更新extras，只不過是先把前面的extras清除，另外FLAG_CANCEL_CURRENT和 FLAG_UPDATE_CURRENT的區(qū)別在于能否新new一個(gè)Intent，F(xiàn)LAG_UPDATE_CURRENT能夠新new一個(gè) Intent，而FLAG_CANCEL_CURRENT則不能，只能使用第一次的Intent。

此外還需要注意參數(shù)： 
int requestCode ： Private request code for the sender (currently not used).

PendingIntent contentIntent = PendingIntent.getActivity(context,
num, intent, PendingIntent.FLAG_UPDATE_CURRENT);

對(duì)于FLAG_UPDATE_CURRENT,如果上面的requestCode 為常量，則對(duì)于先后出現(xiàn)的若干Notification,則所有對(duì)應(yīng)的Intent里面的extra被更新為最新的，就是全部同一為最后一次的。
相反，如果num每次不一樣，則里面的Inent的數(shù)據(jù)沒被更新。
對(duì)于FLAG_CANCEL_CURRENT,則只響應(yīng)最前面的第一條Notifiacation,后面所有的不響應(yīng)....