android中FileObserver的运用

最新推荐文章于 2021-06-03 03:12:10 发布

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本文详细介绍了在Android开发中如何利用FileObserver监听文件夹的变化，包括构造函数的参数设置、onEvent方法的实现以及不同event类型的具体含义。同时讨论了大规模监听时可能遇到的问题和解决策略。

FileObserver，顾名思义，就是文件（夹）观察者，是用来监听文件（夹）的实时变化的，其底层是由linux平台的inotify机制实现的，有兴趣的同学可以自行研究。

那么android中FileObserver的具体用法如何呢？我首次接触是在PackageMangaerService的构造函数中，他被用来监视文件夹（data/app,system/app等），其本身也不难理解，我们只需要集成并重写几个方法就好了。

其中必须重写的有带一个String类型的构造函数已经 onEvent(int event, String path) 。

构造函数必须传入String类型的path值，也就是被监视的文件（夹）路径

onEvent方法则是在监测文件的各种变化。

FileObserver中提供了几种event值我们一起来看一下

    /** Event type: Data was read from a file */
    public static final int ACCESS = 0x00000001;
    /** Event type: Data was written to a file */
    public static final int MODIFY = 0x00000002;
    /** Event type: Metadata (permissions, owner, timestamp) was changed explicitly */
    public static final int ATTRIB = 0x00000004;
    /** Event type: Someone had a file or directory open for writing, and closed it */
    public static final int CLOSE_WRITE = 0x00000008;
    /** Event type: Someone had a file or directory open read-only, and closed it */
    public static final int CLOSE_NOWRITE = 0x00000010;
    /** Event type: A file or directory was opened */
    public static final int OPEN = 0x00000020;
    /** Event type: A file or subdirectory was moved from the monitored directory */
    public static final int MOVED_FROM = 0x00000040;
    /** Event type: A file or subdirectory was moved to the monitored directory */
    public static final int MOVED_TO = 0x00000080;
    /** Event type: A new file or subdirectory was created under the monitored directory */
    public static final int CREATE = 0x00000100;
    /** Event type: A file was deleted from the monitored directory */
    public static final int DELETE = 0x00000200;
    /** Event type: The monitored file or directory was deleted; monitoring effectively stops */
    public static final int DELETE_SELF = 0x00000400;
    /** Event type: The monitored file or directory was moved; monitoring continues */
    public static final int MOVE_SELF = 0x00000800;

简单的实现方法：

        FileObserver fb = new FileObserver("/mnt/sdcard") {
			
			@Override
			public void onEvent(int event, String path) {
				// TODO Auto-generated method stub
				
			}
		};
		//开启监听
		fb.startWatching();
		//结束监听
		fb.stopWatching();

当然，遗憾的是我们只能监听指定的根目录或某个文件，并不能一次监听到他所有的子目录及文件，目前的解决办法是通过遍历将所有文件夹及文件都添加监听，可是FileObserver其实是一个线程，这样大规模的添加势必对程序消耗太大。