asp:UpdatePanel work only when other inputs are valid - asp.net

Question

I have this UpdatePanel:
<asp:ScriptManager ID="CheckManager" runat="server" />
<asp:UpdatePanel ID="checkUsername" runat="server" UpdateMode="Conditional" >
<ContentTemplate>
<asp:Label ID="canUse" runat="server" Text=""/>
<asp:Button ID="check" runat="server" Text="Usable?" onclick="check_Click" />
<asp:TextBox ID="username" runat="server" ></asp:TextBox>
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger controlid="check" eventname="Click" />
</Triggers>
</asp:UpdatePanel>
update code:
protected void check_Click(object sender, EventArgs e)
{
using (HotelEntities h = new HotelEntities())
{
UserHandle u = new UserHandle();
if (u.FindUserByUsername(h, username.Text.ToString()).Any())
{
canUse.ForeColor = Color.Magenta;
canUse.Text = "You cannot use this username";
username.Text = "";
}
else
{
canUse.ForeColor = Color.Green;
canUse.Text = "you can use this username";
}
}
}
but works only when other inputs in form (that have validations e.g. RequiredFieldValidator) are valid .
How can I fix this?

Answer 1

Set CausesValidation="false" for the button for which you do not want validation to be performed when the Button control is clicked.
<asp:Button ID="check" CausesValidation="false" runat="server"
Text="Usable?" onclick="check_Click" />
Button.CausesValidation Property: Gets or sets a value indicating whether validation is performed when the Button control is clicked.

Answer 2

You need to set the ValidationGroup property same with the button and your textbox validations etc. For example you have required field validator near the textBox1. And you have two buttons. If you dont use ValidationGroup, you wont be able to click any of them without validating your inputs.
You may
Check here to see an example