我們都知道要做監聽的話首先需要去重寫Activity的OnkeyDown方法，然而這種辦法只有當Activity在前臺的時候才能用！在後臺的話就不行了。

可以用的方法

利用AccessibilityService（安卓的無障礙輔助功能）

步驟.

1.配置檔案程式碼

<application>  
  <service android:name="你的無障礙輔助類名"  
      android:label="@string/accessibility_service_label">  
    <intent-filter>  
      <action android:name="android.accessibilityservice.AccessibilityService" />  
    </intent-filter>  
  </service>  
  <uses-permission android:name="android.permission.BIND_ACCESSIBILITY_SERVICE" />  
</application> 
 

<?xml version="1.0" encoding="utf-8"?>
<accessibility-service xmlns:android="http://schemas.android.com/apk/res/android"
    android:accessibilityEventTypes="typeAllMask"
    android:accessibilityFeedbackType="feedbackGeneric"
    android:accessibilityFlags="flagRequestFilterKeyEvents"
    android:canRetrieveWindowContent="true"
    android:canRequestFilterKeyEvents="true"  
    android:description="@string/accessibility_description"
    android:notificationTimeout="100"/>
 

3.自己新建一個類去繼承他並重寫他的3個方法 假設你要監聽按鍵的話就重寫OnKeyEvent方法

public class RobMoney extends AccessibilityService {
	 
	private static final String TAG = "dxj";
	private Calendar c = Calendar.getInstance();
	int flag=0;
	@Override
	protected boolean onKeyEvent(KeyEvent event) {
		Log.i(TAG, "onKeyEvent");
		int key = event.getKeyCode();
	
		switch(key){
		case KeyEvent.KEYCODE_VOLUME_DOWN:
			
			
			Intent downintent = new Intent("com.exmaple.broadcaster.KEYDOWN");
			downintent.putExtra("dtime", System.currentTimeMillis());
			if(flag==0){
			sendBroadcast(downintent);
			flag+=1;
			}else if (flag==1) {
				flag=0;
			}
			Log.i(TAG, "KEYCODE_VOLUME_DOWN");
			break;
		case KeyEvent.KEYCODE_VOLUME_UP:
			
			Intent upintent = new Intent("com.exmaple.broadcaster.KEYUP");
			upintent.putExtra("utime", System.currentTimeMillis());
			if(flag==0){
				sendBroadcast(upintent);
				flag+=1;
				}else if (flag==1) {
					flag=0;
				}
			
		Log.i(TAG, "KEYCODE_VOLUME_UP");
	
			break;
			default:
				break;
		}
		return super.onKeyEvent(event);
	}
	
	@Override
	public void onInterrupt() {

	}
	
	@Override
	public void onCreate() {
		Log.i(TAG, "RobMoney::onCreate");
		super.onCreate();
	}

	@Override
	public void onAccessibilityEvent(AccessibilityEvent event) {
		// TODO Auto-generated method stub
		
	}

}