PendingIntent

创建pendingIntent对象
个人理解是一个等待状态的意图对象，常见使用场景app 通知，

1.PendingIntent.getActivity(Context context, int requestCode,
Intent intent, @Flags int flags);
2 PendingIntent.getService(Context context, int requestCode,
@NonNull Intent intent, @Flags int flags)
3 PendingIntent.getBroadcast(Context context, int requestCode,
@NonNull Intent intent, @Flags int flags)
context 上下文对象
requestCode Private request code for the sender 发送者的请求标示
如果requestCode不相同，各个通知之间是不相关的，互不干扰
intent 即可发生的意图对象
flags 两个pendingintent 对象相同即 intent相同并且requestCode 相同时，该标志位才会有作用，
系统给定了4个标志位

/**
* Flag indicating that this PendingIntent can be used only once.
* For use with {@link #getActivity}, {@link #getBroadcast}, and
* {@link #getService}.

If set, after
* {@link #send()} is called on it, it will be automatically
* canceled for you and any future attempt to send through it will fail.
*/

 这个标志表明PendingIntent只能使用一次，他和getActivity，getBroadcast，getService 一起使用。如果设置了这个标志位，调用之后，他将会自动的取消并且以后调用也会失败。public static final int FLAG_ONE_SHOT = 1<<30;---------------------------------------------------------------------------------------/** * Flag indicating that if the described PendingIntent does not * already exist, then simply return null instead of creating it. * For use with {@link #getActivity}, {@link #getBroadcast}, and * {@link #getService}. */ 这个标志表明如果所描述的pendingIntent不存在，使用getActivity getBroadcast和getService 返回null，获取不到实例。 但是在代码中 getActivity是可以获取到pendingintent 的，getBrodcast返回的确实是null。public static final int FLAG_NO_CREATE = 1<<29;---------------------------------------------------------------------------------------/** * Flag indicating that if the described PendingIntent already exists, * the current one should be canceled before generating a new one. * For use with {@link #getActivity}, {@link #getBroadcast}, and * {@link #getService}. <p>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 * {@link #FLAG_UPDATE_CURRENT}. */ 这个标志位表明如果所描述的pendingIntent对象已经存在，之前的pendingintent会被取消在创建新的之前。 你可以用这个创建一个新的pendingintent 对象当你只想改变extra data时， 这样可以确保使用时拿到的是最新的数据。 如果这不是问题，可以考虑使用FLAG_UPDATE_CURRENTpublic static final int FLAG_CANCEL_CURRENT = 1<<28;---------------------------------------------------------------------------------------/** * Flag indicating that if the described PendingIntent already exists, * then keep it but replace its extra data with what is in this new * Intent. For use with {@link #getActivity}, {@link #getBroadcast}, and * {@link #getService}. <p>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. */ 这个标志位表明如果所描述的pendingIntent对象已经存在，他保持原来的对象，只是替换了extra data， 如果你只是想改变extras data，不关心之前的pendingIntent对象，之前的对象会加载新的数据 即使没有明确的给他赋值。public static final int FLAG_UPDATE_CURRENT = 1<<27;