android 4.0 屏蔽home键实现

最近研究锁屏，按照常规的方法，常规方法如下

    public void onAttachedToWindow()  
    {   
            this.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD);      
           super.onAttachedToWindow();   
    }   

但是这个方法到了4.0的系统上就失效了，按home照样会返回桌面。apktool了几个锁屏的软件之后发现其实现方法，即用WindowManager的addview方法将view加到窗口上，加上的时候将view的layoutparamas的type设为LayoutParams.TYPE_SYSTEM_ERROR，这个值sdk的解释为

  public static final int TYPE_SYSTEM_ERROR   
    Since: API Level 1   
    Window type: internal system error windows, appear on top of everything they can.   

 
如果直接这样用会报错，还要在AndroidManifest.xml里面加上权限<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW"/>，ok上完整代码，封装了一个类，其中Lock和hide方法实现锁屏和解锁。

public class LockLayer {  
    private Activity mActivty;  
    private WindowManager mWindowManager;  
    private View mLockView;  
    private LayoutParams mLockViewLayoutParams;  
      
    public LockLayer(Activity act) {  
        mActivty = act;  
        init();  
    }  
  
    private void init(){  
        mWindowManager = mActivty.getWindowManager();  
        mLockViewLayoutParams = new LayoutParams();  
        mLockViewLayoutParams.width = LayoutParams.MATCH_PARENT;  
        mLockViewLayoutParams.height = LayoutParams.MATCH_PARENT;  
        //实现关键  
        mLockViewLayoutParams.type = LayoutParams.TYPE_SYSTEM_ERROR;  
        //apktool value，这个值具体是哪个变量还请网友帮忙  
        mLockViewLayoutParams.flags = 1280;  
    }  
    public void lock() {  
        if(mLockView!=null){  
            mWindowManager.addView(mLockView, mLockViewLayoutParams);  
        }  
    }  
    public void unlock() {  
        if(mWindowManager!=null){  
            mWindowManager.removeView(mLockView);  
        }  
    }  
    public void setLockView(View v){  
        mLockView = v;  
    }  
}