Ajax异步无刷新显示图片

前台：

//图片 
var path = '<%= ResolveUrl("~/Img/") %>'; 
var imgUrl = path +  "/" + result.FileName.substr(result.FileName.lastIndexOf('/') + 1); 
var img = new Image(); 
img.src = imgUrl; 
 

if (!img.complete) {

//无图片

}

else //有图片

{ 
    if (img.width < 500) { //小于最大宽度，按实际宽度显示 
     $("#<%=Image1.ClientID %>").css("width", img.width); 
     } 
     else { //大于等于最大宽度，按最大宽度显示 
    $("#<%=Image1.ClientID %>").css("width", 500); 
     }

}

后台初始化获取第一张图片：

System.Drawing.Image imgPhoto = System.Drawing.Image.FromFile(Server.MapPath(url)); 
int sourceWidth = imgPhoto.Width; 
int sourceHeight = imgPhoto.Height; 
  
if (sourceWidth < 500) 
{ 
Unit width = new Unit(sourceWidth); 
this.Image1.Width = width; 
} 
if (sourceHeight < 350) 
{ 
Unit height = new Unit(sourceHeight); 
this.Image1.Height = height; 
}

ashx文件获取切换的图片数据（使用json返回）：

JavaScriptSerializer serializer = new JavaScriptSerializer(); 
string jsonStr = serializer.Serialize(model); 
  
context.Response.Write(jsonStr);