//dialog创建，context为当前Activity(TestActivity.this)
View myView = LayoutInflater.from(context).
        inflate(R.layout.my_dialog, null, false);
final AlertDialog dialog = new AlertDialog.
        Builder(context).setView(myView).create();
//封装的方法
public void setWindow(AlertDialog dialog){
	//设置点击对话框之外的区域弹窗不消失
	dialog.setCancelable(false);
	//显示对话框
	dialog.show();
	//设置对话框尺寸 window变量初始化时声明即可（Window window）
	window = Objects.requireNonNull(dialog.getWindow());
	window.setLayout(1000, 600);
	//设置背景图全部显示
	window.setBackgroundDrawableResource(android.R.color.transparent);
    }

//对应布局文件(my_dialog.xml)，图片自取
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="200dp"
    android:orientation="vertical"
    android:background="@drawable/new_dialog"
    tools:ignore="ContentDescription" >
</RelativeLayout>