弹出popwindow 背景变暗

package com.example.administrator.popwindowdemo.view;

import android.app.Activity;
import android.content.Context;
import android.graphics.drawable.ColorDrawable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup.LayoutParams;
import android.view.WindowManager;
import android.widget.LinearLayout;
import android.widget.PopupWindow;

import com.example.administrator.popwindowdemo.R;

/**
* Created by Administrator on 2016/4/12.
*/
public class CustomPopwindow extends PopupWindow {
private View mView;
public CustomPopwindow(Activity context,View.OnClickListener itemsOnClick){
super(context);
initView(context,itemsOnClick);
}

private void initView(final Activity context,View.OnClickListener itemsOnClick) {
// TODO Auto-generated method stub
LayoutInflater mInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
mView = mInflater.inflate(R.layout.select_popwindow,null);
LinearLayout ll_select01 = (LinearLayout) mView.findViewById(R.id.ll_select01);
LinearLayout ll_select02 = (LinearLayout) mView.findViewById(R.id.ll_select02);
LinearLayout ll_select03 = (LinearLayout) mView.findViewById(R.id.ll_select03);
//取消按钮
ll_select03.setOnClickListener(new View.OnClickListener() {

public void onClick(View v) {
//销毁弹出框
dismiss();
backgroundAlpha(context, 1f);
}
});
//设置按钮监听
ll_select01.setOnClickListener(itemsOnClick);
ll_select02.setOnClickListener(itemsOnClick);
//设置SelectPicPopupWindow的View
this.setContentView(mView);
//设置SelectPicPopupWindow弹出窗体的宽
this.setWidth(LayoutParams.FILL_PARENT);
//设置SelectPicPopupWindow弹出窗体的高
this.setHeight(LayoutParams.WRAP_CONTENT);
//设置SelectPicPopupWindow弹出窗体可点击
this.setFocusable(true);
//设置PopupWindow可触摸
this.setTouchable(true);
//设置非PopupWindow区域是否可触摸
//        this.setOutsideTouchable(false);
//设置SelectPicPopupWindow弹出窗体动画效果
this.setAnimationStyle(R.style.select_anim);
//实例化一个ColorDrawable颜色为半透明
ColorDrawable dw = new ColorDrawable(0x00000000);
//设置SelectPicPopupWindow弹出窗体的背景
this.setBackgroundDrawable(dw);
backgroundAlpha(context,0.5f);//0.0-1.0
this.setOnDismissListener(new OnDismissListener() {

@Override
public void onDismiss() {
// TODO Auto-generated method stub
backgroundAlpha(context, 1f);
}
});
}
/**
* 设置添加屏幕的背景透明度
* @param bgAlpha
*/
public void backgroundAlpha(Activity context, float bgAlpha)
{
WindowManager.LayoutParams lp = context.getWindow().getAttributes();
lp.alpha = bgAlpha;
context.getWindow().addFlags(WindowManager.LayoutParams.FLAG_DIM_BEHIND);
context.getWindow().setAttributes(lp);
}

}

public class MainActivity extends AppCompatActivity {
private CustomPopwindow customPopwindow;
private Activity mActivity;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mActivity = this;
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);

FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
customPopwindow = new CustomPopwindow(mActivity,itemsOnClick);
customPopwindow.showAtLocation(view,
Gravity.BOTTOM|Gravity.CENTER_HORIZONTAL, 0, 0);
}
});
}
//为弹出窗口实现监听类
private View.OnClickListener itemsOnClick = new View.OnClickListener(){

public void onClick(View v) {
customPopwindow.dismiss();
customPopwindow.backgroundAlpha(mActivity,1f);
switch (v.getId()) {
case R.id.ll_select01:
//do something
break;
case R.id.ll_select02:
//do something

break;
default:
break;
}
}

};

}