Android如何監(jiān)測文件夾內(nèi)容變化詳解

更新時間：2021年12月12日 10:38:41 作者：chaoyu168

最近在開發(fā)android應(yīng)用程序的時候遇到了一個監(jiān)測文件夾的功能,所以下面這篇文章主要給大家介紹了關(guān)于Android如何監(jiān)測文件夾內(nèi)容變化的相關(guān)資料,需要的朋友可以參考下

一. 概述：

android.os包下的FileObserver類是一個用于監(jiān)聽文件訪問、創(chuàng)建、修改、刪除、移動等操作的監(jiān)聽器，基于linux的INotify。FileObserver是個抽象類，必須繼承它才能使用。每個FileObserver對象監(jiān)聽一個單獨的文件或者文件夾，如果監(jiān)視的是一個文件夾，那么文件夾下所有的文件和級聯(lián)子目錄的改變都會觸發(fā)監(jiān)聽的事件。

FileObserver簡介Android.os包下的FileObserver類是一個用于監(jiān)聽文件訪問、創(chuàng)建、修改、刪除、移動等操作的監(jiān)聽器，基于Linux的INotify。

FileObserver是個抽象類，必須繼承它才能使用。每個FileObserver對象監(jiān)聽一個單獨的文件或者文件夾，如果監(jiān)視的是一個文件夾，那么文件夾下所有的文件和級聯(lián)子目錄的改變都會觸發(fā)監(jiān)聽的事件。

二. 監(jiān)聽的事件類型：

ACCESS，即文件被訪問

? ? ?MODIFY，文件被修改

? ? ?ATTRIB，文件屬性被修改，如 chmod、chown、touch 等

? ? ?CLOSE_WRITE，可寫文件被 close

? ? ?CLOSE_NOWRITE，不可寫文件被 close

? ? ?OPEN，文件被 open

? ? ?MOVED_FROM，文件被移走,如 mv

? ? ?MOVED_TO，文件被移來，如 mv、cp

? ? ?CREATE，創(chuàng)建新文件

? ? ?DELETE，文件被刪除，如 rm

? ? ?DELETE_SELF，自刪除，即一個可執(zhí)行文件在執(zhí)行時刪除自己

? ? ?MOVE_SELF，自移動，即一個可執(zhí)行文件在執(zhí)行時移動自己

? ? ?CLOSE，文件被關(guān)閉，等同于(IN_CLOSE_WRITE | IN_CLOSE_NOWRITE)

? ? ?ALL_EVENTS，包括上面的所有事件

三.實例

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(); //開始監(jiān)聽  
        }  
    }  
  
    public void onDestory() {  
        if(null != mFileObserver) mFileObserver.stopWatching(); //停止監(jiān)聽  
    }  
      
    static class SDCardFileObserver extends FileObserver {  
        //mask:指定要監(jiān)聽的事件類型，默認為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: 文件或目錄被訪問, path: " + path);  
                break;  
                  
            case FileObserver.DELETE:  
                System.out.println("event: 文件或目錄被刪除, path: " + path);  
                break;  
                  
            case FileObserver.OPEN:  
                System.out.println("event: 文件或目錄被打開, path: " + path);  
                break;  
                  
            case FileObserver.MODIFY:  
                System.out.println("event: 文件或目錄被修改, path: " + path);  
                break;  
                  
            case FileObserver.CREATE:  
                System.out.println("event: 文件或目錄被創(chuàng)建, path: " + path);  
                break;  
            }  
        }  
          
    }  
}

onEvent是回調(diào)，系統(tǒng)監(jiān)聽到事件后會觸發(fā)此事件，參數(shù)event就是上面所說的事件類型，參數(shù)path就是觸發(fā)事件的目錄，鑒定只針對于該層目錄，其他層次無效。

我們大多數(shù)需要監(jiān)聽path目錄下的所有文件對象的相關(guān)操作，那該如何是好呢？解決問題方法之一就是重新實現(xiàn)FileObserver類，

下面是對FileObserver類的重寫實現(xiàn)過程

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);   
        }   
    }   
}