验证gridview中的数据

Question

我有一个网格如下。

Course         Fee Amount(dynamic textbox)
------         ----------
  A1             15000 
  A2             5000

我有一个文本框（网格外）txtTotalFeeAmount，其值为30000。我的要求是每个A1和A2的费用金额应小于或等于30000.另外A1+A2应小于或等于30000.我该怎么做？

修改

我尝试了以下操作，但它不起作用。

For Each gvRow As GridViewRow In gvCourseFeesDetails.Rows
        Dim lblFeeHeadAmount As System.Web.UI.WebControls.Label = gvRow.FindControl("lblFeeHeadAmount")
        'Dim lblTotalFeeAmount As System.Web.UI.WebControls.Label = gvRow.FindControl("lblTotalFeeAmount")

        totalFeeHead = totalFeeHead + Val(lblFeeHeadAmount.Text)

    Next

    nIndividualFeeHead = Val(txtFeeHeadAmount.Text)
    TotalAmount = totalFeeHead + Val(txtFeeHeadAmount.Text)

    If TotalAmount > Val(txtFeeAmount.Text) Then
        Dim script As String = String.Format("ValidateAmount()")
        ScriptManager.RegisterClientScriptBlock(Me, GetType(Page), UniqueID, script, True)
        Exit Sub
    End If

我的javascript函数：

function ValidateAmount()
    {
        alert('Sum of Fee Head Amount should not exceed the total fee amount entered...!');
        return false;
    }