popupwindow 显示在屏幕中央的办法

	public static void showShareWindow(Activity activity, View parentView, String pageName){
		View mContentView = null;
		V5ShareView mShareView = null;
		if(mContentView == null){
			mContentView = LayoutInflater.from(activity).inflate(R.layout.v5_share_layout, null);
		}
		
		if(mPopUpWindow == null){
			mPopUpWindow = new PopupWindow(mContentView, LayoutParams.MATCH_PARENT,LayoutParams.MATCH_PARENT);
			mPopUpWindow.setBackgroundDrawable(new BitmapDrawable());
			mPopUpWindow.setOutsideTouchable(true);
			mPopUpWindow.setFocusable(true);
		}
		
		if(mShareView == null){
			mShareView = new V5ShareView(mContentView,pageName,activity);
		}
		mShareView.setOnShareViewDismiss(new ShareViewDismiss() {
			
			@Override
			public void dismiss() {
				mPopUpWindow.dismiss();
			}
		});
		mPopUpWindow.showAtLocation(activity.getWindow().getDecorView(), Gravity.CENTER, 0, 0);
	}