如何从javascript调用方法后面的代码？

Question

hello guys i have w method that changes the opacity of an image using on click event and saves this image in a folder. what im trying to do is that i want to call this method using onmouseup event and preview that img automatically in a div . i have this code:

<asp:ScriptManager EnablePartialRendering="true" ID="ScriptManager1" runat="server"></asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional><ContentTemplate>
<input max="10" min="0" name="rangeInput" onmousemove="updateTextInput(this.value);" onmouseup="return showImg()" type="range" runat="server" />
<input id="txtOp" size="3" type="text" value="" runat="server" />
<asp:Button ID="bntChangeOpacity" runat="server" onClick="bntChangeOpacity_Click1" Text="Change Opacity" />
        <div id="placehere"></div>

</ContentTemplate>
</asp:UpdatePanel>

so here i want to replace the bntChangeOpacity_Click1 method to be called onmouseup event

the code behind :

public void bntChangeOpacity_Click1(object sender, EventArgs e)
    {
        string s = txtOp.Value;
        float ss = float.Parse(s);
        float opacityvalue = ss / 10;
        var img = ImageTransparency.ChangeOpacity(Image.FromFile(Server.MapPath("img1.jpg")), opacityvalue);
        img.Save(Server.MapPath("img2.jpg"));

    }

Answer 1

You have to make this as a webmethod innorder to call this from front end;change the method signature as like the following:

[WebMethod]
public static void bntChangeOpacity_Click1(object sender, EventArgs e)
{
    string s = txtOp.Value;
    float ss = float.Parse(s);
    float opacityvalue = ss / 10;
    var img = ImageTransparency.ChangeOpacity(Image.FromFile(HttpContext.Current.Server.MapPath("img1.jpg")), opacityvalue);
    img.Save(HttpContext.Current.Server.MapPath("img2.jpg"));

}

Answer 2

You can use PageMethods for that. Make your method static and decorate it with WebMethod attribute as below

[System.Web.Services.WebMethod]
public static void ChangeOpacity()
    {
        string s = txtOp.Value;
        float ss = float.Parse(s);
        float opacityvalue = ss / 10;
        var img = ImageTransparency.ChangeOpacity(Image.FromFile(Server.MapPath("img1.jpg")), opacityvalue);
        img.Save(Server.MapPath("img2.jpg"));

    }

and call it like function changeOpacity() { PageMethods.ChangeOpacity(); }

from javascript.

you need to change bntChangeOpacity mark up as below.

<asp:Button ID="bntChangeOpacity" runat="server" onClientClick="changeOpacity()" Text="Change Opacity" />

Don't forget to use ScriptManager on page.

Answer 3

Please find sample code of that

http://www.codeproject.com/Articles/180355/Calling-a-code-behind-function-from-JavaScript

Otherwise you need to do Ajaxcall.