OnClientClick不适用于asp.net和vb.net

Question

I try to create a dynamic web solution with ASP.NET and VB.

My webpage looks like this:

<div id="menu" style="position:relative;text-align:center">
        <asp:PlaceHolder runat="server" id="PHimg1" />
        <asp:PlaceHolder runat="server" id="PHimg2" />
        <asp:PlaceHolder runat="server" id="PHimg3" />
        <br />
        <asp:PlaceHolder runat="server" id="PHimg4" />
        <asp:PlaceHolder runat="server" id="PHimg5" />
        <asp:PlaceHolder runat="server" id="PHimg6" />
        <br />
        <asp:PlaceHolder runat="server" id="PHimg7" />
        <asp:PlaceHolder runat="server" id="PHimg8" />
        <asp:PlaceHolder runat="server" id="PHimg9" />
</div>

The VB part like this:

Public Class index
Inherits System.Web.UI.Page

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    Load_Main()
End Sub

Protected Sub Load_Main()
    Dim img1 As New ImageButton()
    Dim img2 As New ImageButton()
    Dim img3 As New ImageButton()
    Dim img4 As New ImageButton()
    Dim img5 As New ImageButton()
    Dim img6 As New ImageButton()

    img1.ImageUrl = "./resources/EssenTrinken.png"
    img1.OnClientClick = "Load_Eating()"

    img2.ImageUrl = "./resources/Einkaufen2-black.png"
    img3.ImageUrl = "./resources/Special-black.png"
    img4.ImageUrl = "./resources/KosmetikWellness.png"
    img5.ImageUrl = "./resources/KulturGeschichte.png"
    img6.ImageUrl = "./resources/Unterhaltung2-black.png"

    PHimg1.Controls.Add(img1)
    PHimg2.Controls.Add(img2)

    PHimg4.Controls.Add(img3)
    PHimg5.Controls.Add(img4)

    PHimg7.Controls.Add(img5)
    PHimg8.Controls.Add(img6)
End Sub

Protected Sub Load_Eating()
    Dim img1 As New ImageButton()
    Dim img2 As New ImageButton()
    Dim img3 As New ImageButton()
    Dim img4 As New ImageButton()
    Dim img5 As New ImageButton()
    Dim img6 As New ImageButton()

    img1.ImageUrl = "./resources/zurueck.png"
    img2.ImageUrl = "./resources/Bars2.png"
    img3.ImageUrl = "./resources/Cafe.png"
    img4.ImageUrl = "./resources/FastFood2.png"
    img5.ImageUrl = "./resources/Restaurant.png"
    img6.ImageUrl = "./resources/Baeckerei.png"

    PHimg1.Controls.Add(img1)
    PHimg2.Controls.Add(img2)

    PHimg3.Controls.Add(img3)
    PHimg4.Controls.Add(img4)

    PHimg5.Controls.Add(img5)
    PHimg6.Controls.Add(img6)
End Sub

End Class

I want that if I click on one of the imagebutton the hole appereance of the frontpage dynamicly changes without loading the hole page new. So I defined several PlacHolder for that.

If I run the webapp but the functionality is not working if I hit the button.

I checked the source and found this tag:

<input type="image" name="ctl03" src="./resources/EssenTrinken.png" onclick="Load_Eating();" />

What is wrong with this solution?

Answer 1

Add to your Page_load a check for IsPostBack

if Not IsPostBack Then
   Load_main()
End If

This will prevent your page_load method to recreate every button and resetting the value for the Image_click event

Answer 2

If you are trying to do this from the code behind, then you need to add the Click event handler:

Protected Sub Load_Main()
    Dim img1 As New ImageButton()    
    AddHandler img1.Click, AddressOf Img1Click
    'rest of your code

and then have some function that does what you want:

Private Sub Img1Click(ByVal sender As Object, ByVal e As ImageClickEventArgs)
    'some code
End Sub

Note, this will cause a postback. It is confusing on how you expect to dynamically change the front page without reloading the page and without using JavaScript...