Field Validator Fires undesirably
<p>I have a page with the following mark up</p>

<pre><code>&lt;%@ Page Title="" Language="C#" MasterPageFile="~/CaseAdmin.master" AutoEventWireup="true" CodeBehind="AddExhibit.aspx.cs" Inherits="Prototype5.AddExhibit" %&gt;
</code></pre>

<p></p>

<pre><code>    &lt;h2 class="style2"&gt;
    &lt;strong&gt;&lt;span style="color: #FFFFFF"&gt;Add Exhibit
    Form&lt;/span&gt;&lt;/strong&gt;&lt;/h2&gt;
&lt;div style="width: 600px"&gt;
&lt;table style="width: 303px" align="left"&gt;
        &lt;tr&gt;
            &lt;td class="style26" style="background-color: #666666"&gt;
                &lt;p class="style5" style="color: #000000; background-color: #666666;"&gt;
                    &lt;strong style="background-color: #666666"&gt;Select Existing Case ID:    
                &lt;/strong&gt;    
                &lt;/p&gt;&lt;/td&gt;
            &lt;td class="" style="background-color: #C0C0C0" align="left"&gt;
                &lt;asp:DropDownList ID="DropDownListcaseid" runat="server" 
                    onselectedindexchanged="DropDownListcaseid_SelectedIndexChanged"&gt;
                &lt;/asp:DropDownList&gt;
                &lt;asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" 
                    ControlToValidate="DropDownListcaseid" 
                    ErrorMessage="Please select a valid case id from the dropdown menu" 
                    ForeColor="Red"&gt;*&lt;/asp:RequiredFieldValidator&gt;
            &lt;/td&gt;
        &lt;/tr&gt;
        &lt;tr&gt;
            &lt;td class="style4" colspan="2"&gt;
                &amp;nbsp;&lt;/td&gt;
        &lt;/tr&gt;
    &lt;/table&gt;

    &lt;asp:SqlDataSource ID="SqlDataSource1" runat="server" 
        ConnectionString="&lt;%$ ConnectionStrings:CMSSQL3ConnectionString1 %&gt;" 
        SelectCommand="SELECT [CaseID] FROM [Cases]"&gt;&lt;/asp:SqlDataSource&gt;

&lt;/div&gt;
&lt;div style="width: 603px; height: 75px; "&gt;

    &lt;table style="height: 66px; width: 598px; top: 277px; left: 268px;" 
        align="left"&gt;
        &lt;tr&gt;
            &lt;td class="bold" 
                style="color: #000000; background-color: #666666; width: 127px;"&gt;
                &lt;strong&gt;Exhibit Type&lt;/strong&gt;&lt;/td&gt;
            &lt;td class="bold" style="background-color: #666666; width: 228px;"&gt;
                &lt;span style="color: #000000"&gt;Exhibit Image&lt;/td&gt;
            &lt;td class="bold" style="background-color: #666666; width: 111px;"&gt;
                &lt;span style="color: #000000"&gt;Stored Location&lt;/span&gt;&lt;/td&gt;
            &lt;td class="bold" style="background-color: #666666; color: #000000;"&gt;
                Officer ID&lt;/span&gt;&lt;/td&gt;
        &lt;/tr&gt;
        &lt;tr&gt;
            &lt;td class="style32" style="background-color: #C0C0C0; width: 127px;"&gt;
                &lt;asp:DropDownList ID="exhibitTypeDropDownList" runat="server"&gt;
                    &lt;asp:ListItem&gt;&lt;/asp:ListItem&gt;
                    &lt;asp:ListItem&gt;Hard Disk&lt;/asp:ListItem&gt;
                    &lt;asp:ListItem&gt;Pen Drive&lt;/asp:ListItem&gt;
                    &lt;asp:ListItem&gt;Laptop&lt;/asp:ListItem&gt;
                    &lt;asp:ListItem&gt;Palm Devce&lt;/asp:ListItem&gt;
                    &lt;asp:ListItem&gt;Mobile Phone&lt;/asp:ListItem&gt;
                    &lt;asp:ListItem&gt;Tablet PC&lt;/asp:ListItem&gt;
                    &lt;asp:ListItem&gt;Pager&lt;/asp:ListItem&gt;
                &lt;/asp:DropDownList&gt;
                &lt;asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" 
                    ControlToValidate="exhibitTypeDropDownList" 
                    ErrorMessage="Please Enter the type of exhibit. eg. Harddisk" 
                    ForeColor="Red" ondisposed="addExhibitButton_Click"&gt;*&lt;/asp:RequiredFieldValidator&gt;
            &lt;/td&gt;
            &lt;td class="style28" style="background-color: #C0C0C0; width: 228px;"&gt;
                &lt;asp:FileUpload ID="exhibitImageFileUpload" runat="server" /&gt;
            &lt;/td&gt;
            &lt;td class="style20" style="background-color: #C0C0C0; width: 111px;"&gt;
                &lt;asp:DropDownList ID="storedLocationDropDownList" runat="server"&gt;
                    &lt;asp:ListItem&gt;&lt;/asp:ListItem&gt;
                    &lt;asp:ListItem&gt;B-15/4&lt;/asp:ListItem&gt;
                    &lt;asp:ListItem&gt;B-10/1&lt;/asp:ListItem&gt;
                    &lt;asp:ListItem&gt;B-5/4&lt;/asp:ListItem&gt;
                &lt;/asp:DropDownList&gt;
                &lt;asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" 
                    ControlToValidate="storedLocationDropDownList" 
                    ErrorMessage="Please enter a valid stored location" ForeColor="Red" 
                    ondisposed="addExhibitButton_Click"&gt;*&lt;/asp:RequiredFieldValidator&gt;
            &lt;/td&gt;
            &lt;td class="style30" style="background-color: #C0C0C0"&gt;
                &lt;asp:DropDownList ID="DropDownList1" runat="server" 
                    DataSourceID="officersSqlDataSource" DataTextField="PoliceID" 
                    DataValueField="PoliceID" Width="79px" Height="26px"&gt;
                &lt;/asp:DropDownList&gt;
                &lt;asp:RequiredFieldValidator ID="RequiredFieldValidator4" runat="server" 
                    ControlToValidate="DropDownList1" 
                    ErrorMessage="Please select a valid Officer id from the dropdown list" 
                    ForeColor="Red" ondisposed="addExhibitButton_Click"&gt;*&lt;/asp:RequiredFieldValidator&gt;
            &lt;/td&gt;
        &lt;/tr&gt;
    &lt;/table&gt;

&lt;/div&gt;
&lt;div style="width: 609px; height: 23px;"&gt;
                &lt;/div&gt;
&lt;div style="margin-top:12px; width: 232px; text-align:left; font-size:1.3em;"&gt;

    &lt;asp:SqlDataSource ID="officersSqlDataSource" 
        runat="server" 
        ConnectionString="&lt;%$ ConnectionStrings:CMSSQL3ConnectionString1 %&gt;" 
        SelectCommand="SELECT PoliceID FROM PoliceOfficers"&gt;&lt;/asp:SqlDataSource&gt;
    &lt;table align="left"&gt;
        &lt;tr&gt;
            &lt;td align="center"&gt;
                &lt;asp:ValidationSummary ID="ValidationSummary1" runat="server" ForeColor="Red" 
                    HeaderText="The following errors occured." /&gt;
            &lt;/td&gt;
        &lt;/tr&gt;
    &lt;/table&gt;

    &lt;/div&gt;
    &lt;div style="margin-top:12px; width: 456px;"&gt;

        &lt;table  style="width: 450px" align="left"&gt;
            &lt;tr&gt;
                &lt;td align="center" colspan="3"&gt;
                    &lt;asp:Label ID="messageLabel" runat="server" BackColor="White" ForeColor="Red" 
                        Visible="False"&gt;&lt;/asp:Label&gt;
                &lt;/td&gt;
            &lt;/tr&gt;
            &lt;tr&gt;
                &lt;td align="center" style="width: 96px"&gt;
                    &lt;asp:Button ID="cancelButton" runat="server" Text="Cancel" 
                        onclick="cancelButton_Click" height="26px" width="101px" /&gt;
                &lt;/td&gt;
                &lt;td  style="width: 237px"&gt;
                    &amp;nbsp;&lt;/td&gt;
                &lt;td align="center"&gt;
                    &lt;asp:Button ID="addExhibitButton" runat="server" Text="Add Exhibit" 
                        onclick="addExhibitButton_Click" /&gt;
                &lt;/td&gt;
            &lt;/tr&gt;
        &lt;/table&gt;

    &lt;/div&gt;
</code></pre>

<p></p>

<p>and the following interface look
<img src="http://i.stack.imgur.com/dUikM.jpg" alt="alt text"></p>

<p>I wish to perform validation on the page only when the "add exhibit button" is clicked. so in my code behind, i used an "if(page.isvalid)" to check for page validation when the button is clicked. However any other button i click fires the validation as well... I presume its because every button click tries to load a page and that calls the validator to action. how do i allow work around the validation such that, only the " add exhibit button" triggers the page validation?</p>
