Android Popupwindow弹出窗口

package com.example.day03window;

import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.PopupWindow;

public class MainActivity extends AppCompatActivity {

    private Button button;
    private Button bu;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button=findViewById(R.id.button);
        //点击
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                PopupWindow window=new PopupWindow();

                View view= LayoutInflater.from(MainActivity.this).inflate(R.layout.item,null);
                window.setContentView(view);

                window.setWidth(ViewGroup.LayoutParams.MATCH_PARENT);
                window.setHeight(ViewGroup.LayoutParams.WRAP_CONTENT);

                //获取焦点 点击空白处可以消除视图
                window.setFocusable(true);
                window.setOutsideTouchable(true);
                //设置背景
                window.setBackgroundDrawable(new ColorDrawable(Color.BLUE));
                window.showAtLocation(button,Gravity.BOTTOM,0,0);
//                window.showAsDropDown(button);
            }
        });
    }
}