Android PendingIntent解读

/**
 * A description of an Intent and target action to perform with it.  Instances
 * of this class are created with {@link #getActivity},
 * {@link #getBroadcast}, {@link #getService}; the returned object can be
 * handed to other applications so that they can perform the action you
 * described on your behalf at a later time.
 *
 * <p>By giving a PendingIntent to another application,
 * you are granting it the right to perform the operation you have specified
 * as if the other application was yourself (with the same permissions and
 * identity).  As such, you should be careful about how you build the PendingIntent:
 * often, for example, the base Intent you supply will have the component
 * name explicitly set to one of your own components, to ensure it is ultimately
 * sent there and nowhere else.
 *
 * <p>A PendingIntent itself is simply a reference to a token maintained by
 * the system describing the original data used to retrieve it.  This means
 * that, even if its owning application's process is killed, the
 * PendingIntent itself will remain usable from other processes that
 * have been given it.  If the creating application later re-retrieves the
 * same kind of PendingIntent (same operation, same Intent action, data,
 * categories, and components, and same flags), it will receive a PendingIntent
 * representing the same token if that is still valid, and can thus call
 * {@link #cancel} to remove it.
 */
public final class PendingIntent implements Parcelable {}

Intent 是及时启动，intent 随所在的activity 消失而消失。
PendingIntent 可以看作是对intent的包装，通常通过getActivity,getBroadcast ,getService来得到pendingintent的实例，当前activity并不能马上启动它所包含的intent,而是在外部执行pendingintent时，调用intent的。正由于pendingintent中 保存有当前App的Context，使它赋予外部App一种能力，使得外部App可以如同当前App一样的执行pendingintent里的Intent， 就算在执行时当前App已经不存在了，也能通过存在pendingintent里的Context照样执行Intent。另外还可以处理intent执行后的操作。常和Alermanger 和Notificationmanager一起使用。

与Intent区别：Intent一般是用作Activity、Sercvice、BroadcastReceiver之间传递数据，而Pendingintent，一般用在Notification上，可以理解为延迟执行的intent，PendingIntent是对Intent一个包装。

用法：
  

/** @param context The Context in which this PendingIntent should start
     * the service.
     * @param requestCode Private request code for the sender (currently
     * not used).
     * @param intent An Intent describing the service to be started.
     * @param flags May be {@link #FLAG_ONE_SHOT}, {@link #FLAG_NO_CREATE},
     * {@link #FLAG_CANCEL_CURRENT}, {@link #FLAG_UPDATE_CURRENT},
     * or any of the flags as supported by
     * {@link Intent#fillIn Intent.fillIn()} to control which unspecified parts
     * of the intent that can be supplied when the actual send happens.
     *
     * @return Returns an existing or new PendingIntent matching the given
     * parameters.  May return null only if {@link #FLAG_NO_CREATE} has been
     * supplied.
     */

PendingIntent getActivity(Context context, int requestCode,Intent intent, int flags);
PendingIntent getBroadcast(Context context, int requestCode,Intent intent, int flags);
PendingIntent getService(Context context, int requestCode,Intent intent, int flags);