Android 多檔案監聽的實現

android.os下的FileObserver類是一個用於監聽檔案訪問、建立、修改、刪除、移動等操作的監聽器，但是該監聽只針對監聽的那個檔案目錄下的一級子檔案起作用，

而對它子目錄下的檔案目錄則不能夠實現。如下樣本：

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(); //開始監聽        }    }    public void onDestory() {        if(null != mFileObserver) mFileObserver.stopWatching(); //停止監聽    }        static class SDCardFileObserver extends FileObserver {        //mask:指定要監聽的事件類型，預設為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: 檔案或目錄被訪問, path: " + path);                break;                            case FileObserver.DELETE:                System.out.println("event: 檔案或目錄被刪除, path: " + path);                break;                            case FileObserver.OPEN:                System.out.println("event: 檔案或目錄被開啟, path: " + path);                break;                            case FileObserver.MODIFY:                System.out.println("event: 檔案或目錄被修改, path: " + path);                break;                            case FileObserver.CREATE:            System.out.println("event: 檔案或目錄被建立, path: " + path);            break;            }        }            }}

onEvent是回調，系統監聽到事件後會觸發此事件，參數event就是上面所說的事件類型，參數path就是觸發事件的目錄，評鑑只針對於該層目錄，其他層次無效。

我們大多數需要監聽path目錄下的所有檔案對象的相關操作，那該如何是好呢？解決問題方法之一就是重新實現FileObserver類，

下面是對FileObserver類的重寫實現過程

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 RecursiveFileObserver extends FileObserver {      /** Only modification events */     public static int CHANGES_ONLY = CREATE | DELETE | CLOSE_WRITE             | DELETE_SELF | MOVE_SELF | MOVED_FROM | MOVED_TO;      List mObservers;     String mPath;     int mMask;      public RecursiveFileObserver(String path) {         this(path, ALL_EVENTS);     }      public RecursiveFileObserver(String path, int mask) {         super(path, mask);         mPath = path;         mMask = mask;     }      @Override     public void startWatching() {         if (mObservers != null)             return;          mObservers = new ArrayList();         Stack stack = new Stack();         stack.push(mPath);          while (!stack.isEmpty()) {             String parent = (String)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 = (SingleFileObserver) mObservers.get(i);             sfo.startWatching();         }     };      @Override     public void stopWatching() {         if (mObservers == null)             return;          for (int i = 0; i < mObservers.size(); i++) {             SingleFileObserver sfo = (SingleFileObserver) 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;             RecursiveFileObserver.this.onEvent(event, newPath);         }     } } 

修改之後的FileObserver就可以實現對path目錄下所有檔案的操作都能監聽到了。