WindowManager.LayoutParams参数说明

谁能详细的解析以下WindowManager.LayoutParams参数的用处阿？顺便说明以下下面代码的意思。请指教？
if (mKeyguardHost == null) {
            if (DEBUG) Log.d(TAG, "keyguard host is null, creating it...");            mKeyguardHost = new KeyguardViewHost(mContext, mCallback);            final int stretch = ViewGroup.LayoutParams.MATCH_PARENT;
            int flags = WindowManager.LayoutParams.FLAG_FORCE_NOT_FULLSCREEN
                    | WindowManager.LayoutParams.FLAG_SHOW_WALLPAPER
                    | WindowManager.LayoutParams.FLAG_KEEP_SURFACE_WHILE_ANIMATING
                    /*| WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN
                    | WindowManager.LayoutParams.FLAG_LAYOUT_INSET_DECOR*/ ;
            if (!mNeedsInput) {
                flags |= WindowManager.LayoutParams.FLAG_ALT_FOCUSABLE_IM;
            }
            WindowManager.LayoutParams lp = new WindowManager.LayoutParams(
                    stretch, stretch, WindowManager.LayoutParams.TYPE_KEYGUARD,
                    flags, PixelFormat.TRANSLUCENT);
            lp.softInputMode = WindowManager.LayoutParams.SOFT_INPUT_ADJUST_PAN;
            lp.windowAnimations = com.android.internal.R.style.Animation_LockScreen;
            lp.screenOrientation = ActivityInfo.SCREEN_ORIENTATION_NOSENSOR;
            lp.setTitle("Keyguard");
            mWindowLayoutParams = lp;            mViewManager.addView(mKeyguardHost, lp);
        }