Android如何監測文件夾內容變化詳解
一. 概述:
android.os包下的FileObserver類是一個用於監聽文件訪問、創建、修改、刪除、移動等操作的監聽器,基於linux的INotify。FileObserver是個抽象類,必須繼承它才能使用。每個FileObserver對象監聽一個單獨的文件或者文件夾,如果監視的是一個文件夾,那麼文件夾下所有的文件和級聯子目錄的改變都會觸發監聽的事件。
FileObserver簡介Android.os包下的FileObserver類是一個用於監聽文件訪問、創建、修改、刪除、移動等操作的監聽器,基於Linux的INotify。
FileObserver是個抽象類,必須繼承它才能使用。每個FileObserver對象監聽一個單獨的文件或者文件夾,如果監視的是一個文件夾,那麼文件夾下所有的文件和級聯子目錄的改變都會觸發監聽的事件。
二. 監聽的事件類型:
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,創建新文件
DELETE,文件被刪除,如 rm
DELETE_SELF,自刪除,即一個可執行文件在執行時刪除自己
MOVE_SELF,自移動,即一個可執行文件在執行時移動自己
CLOSE,文件被關閉,等同於(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,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: 文件或目錄被創建, 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,鑒定隻針對於該層目錄,其他層次無效。
我們大多數需要監聽path目錄下的所有文件對象的相關操作,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 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); } } }
總結
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