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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