Android如何监测文件夹内容变化详解，

来源：开发者投稿于 2022-01-08 被查看 36951 次评论：239

Android如何监测文件夹内容变化详解，

一. 概述：

android.os包下的FileObserver类是一个用于监听文件访问、创建、修改、删除、移动等操作的监听器，基于linux的INotify。FileObserver是个抽象类，必须继承它才能使用。每个FileObserver对象监听一个单独的文件或者文件夹，如果监视的是一个文件夹，那么文件夹下所有的文件和级联子目录的改变都会触发监听的事件。

FileObserver简介Android.os包下的FileObserver类是一个用于监听文件访问、创建、修改、删除、移动等操作的监听器，基于Linux的INotify。

FileObserver是个抽象类，必须继承它才能使用。每个FileObserver对象监听一个单独的文件或者文件夹，如果监视的是一个文件夹，那么文件夹下所有的文件和级联子目录的改变都会触发监听的事件。

二. 监听的事件类型：

ACCESS，即文件被访问

MODIFY，文件被修改

ATTRIB，文件属性被修改，如 chmod、chown、touch 等

CLOSE_WRITE，可写文件被 close

CLOSE_NOWRITE，不可写文件被 close

OPEN，文件被 open

MOVED_FROM，文件被移走,如 mv

MOVED_TO，文件被移来，如 mv、cp

CREATE，创建新文件

DELETE，文件被删除，如 rm

DELETE_SELF，自删除，即一个可执行文件在执行时删除自己

MOVE_SELF，自移动，即一个可执行文件在执行时移动自己

CLOSE，文件被关闭，等同于(IN_CLOSE_WRITE | IN_CLOSE_NOWRITE)

ALL_EVENTS，包括上面的所有事件

三.实例

import com.example.androidemail.R;  
import com.example.androidemail.R.layout;  
  
import android.app.Activity;  
import android.os.Bundle;  
import android.os.Environment;  
import android.os.FileObserver;  
  
public class AndroidFileListenerActivity extends Activity {  
    private FileObserver mFileObserver;  
      
    /** Called when the activity is first created. */  
    @Override  
    public void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.activity_main);  
          
        if(null == mFileObserver) {  
            mFileObserver = new SDCardFileObserver(Environment.getExternalStorageDirectory().getPath());  
            mFileObserver.startWatching(); //开始监听  
        }  
    }  
  
    public void onDestory() {  
        if(null != mFileObserver) mFileObserver.stopWatching(); //停止监听  
    }  
      
    static class SDCardFileObserver extends FileObserver {  
        //mask:指定要监听的事件类型，默认为FileObserver.ALL_EVENTS  
        public SDCardFileObserver(String path, int mask) {  
            super(path, mask);  
        }  
  
        public SDCardFileObserver(String path) {  
            super(path);  
        }  
  
        @Override  
        public void onEvent(int event, String path) {  
            final int action = event & FileObserver.ALL_EVENTS;  
            switch (action) {  
            case FileObserver.ACCESS:  
                System.out.println("event: 文件或目录被访问, path: " + path);  
                break;  
                  
            case FileObserver.DELETE:  
                System.out.println("event: 文件或目录被删除, path: " + path);  
                break;  
                  
            case FileObserver.OPEN:  
                System.out.println("event: 文件或目录被打开, path: " + path);  
                break;  
                  
            case FileObserver.MODIFY:  
                System.out.println("event: 文件或目录被修改, path: " + path);  
                break;  
                  
            case FileObserver.CREATE:  
                System.out.println("event: 文件或目录被创建, path: " + path);  
                break;  
            }  
        }  
          
    }  
}

onEvent是回调，系统监听到事件后会触发此事件，参数event就是上面所说的事件类型，参数path就是触发事件的目录，鉴定只针对于该层目录，其他层次无效。

我们大多数需要监听path目录下的所有文件对象的相关操作，那该如何是好呢？解决问题方法之一就是重新实现FileObserver类，

下面是对FileObserver类的重写实现过程

import java.io.File;  
import java.util.ArrayList;  
import java.util.List;  
import java.util.Stack;  
  
import android.os.FileObserver;  
import android.util.Log;  
  
@SuppressWarnings(value = { "rawtypes", "unchecked" })   
public class MultiFileObserver extends FileObserver {   
   
   /** Only modification events */   
    public static int CHANGES_ONLY = CREATE | MODIFY |DELETE | CLOSE_WRITE     
            | DELETE_SELF | MOVE_SELF | MOVED_FROM | MOVED_TO;   
   
    private List<SingleFileObserver> mObservers;   
    private String mPath;   
    private int mMask;   
   
    public MuityFileObserver(String path) {   
        this(path, ALL_EVENTS);   
    }   
   
    public MuityFileObserver(String path, int mask) {   
        super(path, mask);   
        mPath = path;   
        mMask = mask;   
    }   
   
    @Override   
    public void startWatching() {   
        if (mObservers != null)   
            return;   
   
        mObservers = new ArrayList<SingleFileObserver>();   
        Stack<String> stack = new Stack<String>();   
        stack.push(mPath);   
   
        while (!stack.isEmpty()) {   
            String parent = stack.pop();   
            mObservers.add(new SingleFileObserver(parent, mMask));   
            File path = new File(parent);   
            File[] files = path.listFiles();   
            if (null == files)   
                continue;   
            for (File f : files) {   
                if (f.isDirectory() && !f.getName().equals(".")   
                        && !f.getName().equals("..")) {   
                    stack.push(f.getPath());   
                }   
            }   
        }   
   
        for (int i = 0; i < mObservers.size(); i++) {   
            SingleFileObserver sfo =  mObservers.get(i);   
            sfo.startWatching();   
        }   
    };   
   
    @Override   
    public void stopWatching() {   
        if (mObservers == null)   
            return;   
   
        for (int i = 0; i < mObservers.size(); i++) {   
            SingleFileObserver sfo = mObservers.get(i);   
            sfo.stopWatching();   
        }   
           
        mObservers.clear();   
        mObservers = null;   
    };   
  
   
    @Override   
    public void onEvent(int event, String path) {   
        switch (event) {   
        case FileObserver.ACCESS:   
            Log.i("RecursiveFileObserver", "ACCESS: " + path);   
            break;   
        case FileObserver.ATTRIB:   
            Log.i("RecursiveFileObserver", "ATTRIB: " + path);   
            break;   
        case FileObserver.CLOSE_NOWRITE:   
            Log.i("RecursiveFileObserver", "CLOSE_NOWRITE: " + path);   
            break;   
        case FileObserver.CLOSE_WRITE:   
            Log.i("RecursiveFileObserver", "CLOSE_WRITE: " + path);   
            break;   
        case FileObserver.CREATE:   
            Log.i("RecursiveFileObserver", "CREATE: " + path);   
            break;   
        case FileObserver.DELETE:   
            Log.i("RecursiveFileObserver", "DELETE: " + path);   
            break;   
        case FileObserver.DELETE_SELF:   
            Log.i("RecursiveFileObserver", "DELETE_SELF: " + path);   
            break;   
        case FileObserver.MODIFY:   
            Log.i("RecursiveFileObserver", "MODIFY: " + path);   
            break;   
        case FileObserver.MOVE_SELF:   
            Log.i("RecursiveFileObserver", "MOVE_SELF: " + path);   
            break;   
        case FileObserver.MOVED_FROM:   
            Log.i("RecursiveFileObserver", "MOVED_FROM: " + path);   
            break;   
        case FileObserver.MOVED_TO:   
            Log.i("RecursiveFileObserver", "MOVED_TO: " + path);   
            break;   
        case FileObserver.OPEN:   
            Log.i("RecursiveFileObserver", "OPEN: " + path);   
            break;   
        default:   
            Log.i("RecursiveFileObserver", "DEFAULT(" + event + " : " + path);   
            break;   
        }   
    }   
   
    /** 
     * Monitor single directory and dispatch all events to its parent, with full 
     * path. 
     */   
    class SingleFileObserver extends FileObserver {   
        String mPath;   
   
        public SingleFileObserver(String path) {   
            this(path, ALL_EVENTS);   
            mPath = path;   
        }   
   
        public SingleFileObserver(String path, int mask) {   
            super(path, mask);   
            mPath = path;   
        }   
   
        @Override   
        public void onEvent(int event, String path) {   
            String newPath = mPath + "/" + path;   
            MultiFileObserver .this.onEvent(event, newPath);   
        }   
    }   
}

总结

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Android如何监测文件夹内容变化详解，