如何在textchanged事件上阻止或禁用按钮的回发？

debugcn 发表于 Dev

达伍德·阿巴斯（Dawood Abbas）

对于我的“用户名”字段，我正在检查存在名称，如果存在则将在label。引发错误。那么如何禁用按钮的单击事件或回发？

protected void txtUserName_TextChanged(object sender, EventArgs e)  
{  
    try  
    {  
        string userName = txtUserName.Text;  
        if (connection.State == ConnectionState.Closed)  
            connection.Open();

        command = new SqlCommand();
        command.CommandText = "Get_UserName";
        command.CommandType = CommandType.StoredProcedure;
        command.Parameters.AddWithValue("@userName", userName);
        command.Connection = connection;

        SqlDataReader reader = command.ExecuteReader();
        if (reader.HasRows)
        {
            lblUserNameError.Text = "Alredy Exist";
            lblUserNameError.Visible = true;
            //btnSave.Enabled = false; 
             //btnSave.onClientClick="return false";
             someID.Attributes.Add("onClick", "return false;");
        }
        else
        {
            lblUserNameError.Visible = false;               
        }
    }
    catch (Exception ex)
    {
        Response.Write(ex.Message);
    }  
    finally //Close db Connection if it is open....  
    {
        if (connection.State == ConnectionState.Open)
            connection.Close();
    }
}

以上三种方式，我仍然可以在点击按钮后返回页面。

达伍德·阿巴斯（Dawood Abbas）

我的文本框在UpdatePanel内，按钮也必须在UpdatePanel内，否则它不会刷新。

<asp:updatepanel id="uptxtUserName" runat="server" xmlns:asp="#unknown"><contenttemplate>
                                <asp:textbox id="txtUserName" runat="server" tabindex="8" autopostback="true">
                                        ontextchanged="txtUserName_TextChanged"></asp:textbox>
                                        <asp:label id="lblUserNameError" runat="server" visible="false" forecolor="Red"></asp:label>
            <asp:requiredfieldvalidator id="reqUName" controltovalidate="txtUserName" errormessage="Required" class="error" runat="server" forecolor="Red">
            </asp:requiredfieldvalidator>
            </contenttemplate>
                <triggers>
                    <asp:asyncpostbacktrigger controlid="txtUserName" eventname="TextChanged" />
                    <asp:asyncpostbacktrigger controlid="btnSave" eventname="Click" />
                    <asp:asyncpostbacktrigger controlid="btnCancel" eventname="Click" />
                </triggers>
            </asp:updatepanel>
<pre lang="xml"><asp:UpdatePanel ID="upbtnSave" runat="server"><ContentTemplate>
                        <asp:Button ID="btnSave" Text="Save" runat="server" TabIndex="31" class="btn btn-success" onclick="btnSave_Click"></asp:Button>
                                <asp:Button ID="btnCancel" Text="Cancel" CausesValidation="false" runat="server" TabIndex="32" class="btn" onclick="btnCancel_Click"></asp:Button>
                                    </ContentTemplate>
                                        <Triggers>
                                            <asp:AsyncPostBackTrigger ControlID="btnSave" EventName="Click" />
                                            <asp:AsyncPostBackTrigger ControlID="btnCancel" EventName="Click" />
                                            <asp:AsyncPostBackTrigger ControlID="txtUserName" EventName="TextChanged" />
                                        </Triggers>
                                    </asp:UpdatePanel>

那么后面的代码将如下所示

protected void txtUserName_TextChanged(object sender, EventArgs e)   
        {     
            try   
            {    
                string userName = txtUserName.Text;
                if (connection.State == ConnectionState.Closed)
                    connection.Open();


            command = new SqlCommand();
            command.CommandText = &quot;Get_UserName&quot;;
            command.CommandType = CommandType.StoredProcedure;
            command.Parameters.AddWithValue(&quot;@userName&quot;, userName);
            command.Connection = connection;

            SqlDataReader reader = command.ExecuteReader();
            if (reader.HasRows)
            {
                lblUserNameError.Text = &quot;Alredy Exist&quot;;
                lblUserNameError.Visible = true;
                btnSave.OnClientClick = &quot;return false;&quot;;
            }
            else
            {
                lblUserNameError.Visible = false;
                btnSave.OnClientClick = &quot;return true;&quot;;
            }
        }
        catch (Exception ex)
        {
            Response.Write(ex.Message);
        }
        finally //Close db Connection if it is open....
        {
            if (connection.State == ConnectionState.Open)
                connection.Close();
            connection.Close();
            command.Dispose();
        }
    }

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