Easily Getting HTML PostBack Data in ASP.NET

Shared modules we use to return sanitised input data from user forms without the need for Session State, complex PostBack handling and without errors in dropdown lists

Flexible, powerful and secure

There have been a few instances in application development phases where we have needed to get post data earlier than the normal life cycle of the controls. While not a major coding issue to work around, we wanted to make it as small a module as possible.

When combined with a switching function, you can tell the application to pull the data from a data source or the postback depending on situation.

We have used this in production environments in a few cases, and it is used liberally within our Ousia CMS application;

Creating a fully updatable asp:GridView control, almost simulating an Excel sheet
Setting custom form asp:DropDown selected values without errors
Removing session state from applications to reduce payload
Early application updating (before controls are fully created)
Sanatise your data, returns the right data type.

We will set the code out below, and then go into some detail after.

ASP.NET

    Public Shared Function GetPostBackValue(ByVal r As HttpRequest, c As Control) As String        Dim ret As String = ""        If Not IsNothing(r.Form) Then If Not IsNothing(r.Form.Item(c.UniqueID)) Then ret = r.Form.Item(c.UniqueID)        Return ret    End Function    Public Shared Function GetPostBackValueString(ByVal r As HttpRequest, c As String) As String        Dim ret As String = ""        If Not IsNothing(r.Form) Then If Not IsNothing(r.Form.Item(c)) Then ret = r.Form.Item(c)        Return ret    End Function    Public Shared Function GetPostBackDate(ByVal r As HttpRequest, c As Control) As String        Dim ret As String = ""        If Not IsNothing(r.Form) Then If Not IsNothing(r.Form.Item(c.UniqueID)) Then ret = r.Form.Item(c.UniqueID)        Dim retS As String = ""        If IsDate(ret) Then retS = ret        Return retS    End Function    Public Shared Function GetPostBackDateString(ByVal r As HttpRequest, c As String) As String        Dim ret As String = ""        If Not IsNothing(r.Form) Then If Not IsNothing(r.Form.Item(c)) Then ret = r.Form.Item(c)        Dim retS As String = ""        If IsDate(ret) Then retS = ret        Return retS    End Function    Public Shared Function GetPostBackCheck(ByVal r As HttpRequest, c As Control) As Boolean        Dim ret As String = ""        If Not IsNothing(r.Form) Then If Not IsNothing(r.Form.Item(c.UniqueID)) Then ret = r.Form.Item(c.UniqueID)        Dim retS As Boolean = False        If ret = "on" Then retS = True        Return retS    End Function    Public Shared Function GetPostBackCheckString(ByVal r As HttpRequest, c As String) As Boolean        Dim ret As String = ""        If Not IsNothing(r.Form) Then            If Not IsNothing(r.Form.Item(c)) Then                ret = r.Form.Item(c).ToString            End If        End If        Dim retS As Boolean = False        If ret = "on" Or ret = "True" Or ret = "true" Or ret = "1" Then retS = True        Return retS    End Function    Public Shared Function UpdateValueSwitch(u As Boolean, d As String, p As String) As String        Dim ret As String = ""        If u = True Then            If p = "" Then                ret = d            Else                ret = p            End If        Else            ret = d        End If        Return ret    End Function    Public Shared Function ClearInt(v As String) As Int64        Dim i As Int64 = 0        If IsNumeric(v) Then i = v        Return i    End Function    Public Shared Function ClearDou(v As String) As Double        Dim i As Double = 0        If IsNumeric(v) Then i = v        Return i    End Function    Public Shared Function SQLStr(v As String) As String        Dim i As String = "NULL"        If Not IsNothing(v) Then If v <> "" Then i = "N'" + Replace(v, "'", "''") + "'"        Return i    End Function    Public Shared Function SQLInt(v As String) As String        Dim i As String = "NULL"        If Not IsNothing(v) Then If IsNumeric(v) = True Then i = Replace(v, "'", "''")        Return i    End Function    Public Shared Function SQLDate(v As String) As String        Dim i As String = "NULL"        If Not IsNothing(v) Then If IsDate(v) = True Then i = "'" + Date.Parse(v).ToString("yyyy-MM-dd HH:mm:ss") + "'"        Return i    End Function    Public Shared Function SQLBit(v As String) As String        Dim i As String = "0"        If Not IsNothing(v) Then If v = "True" Then i = "1"        Return i    End Function

What it is doing

We know that the majority of people come here to get some examples and then adapt it to there needs, but those of you who want to work out what it is doing keep reading.

GetPostBackValue, GetPostBackCheck and GetPostBackDate will return the relevant value from the values passed in, which are the request (contains all posted information), and the control (the form value). The check and date versions simply check the datatype provided is relevant.

ClearInt, ClearDou, ClearDate return the relevant datatype from a string, used as a basic switch to assign data that needs to be a set type.

SQLStr, SQLInt, SQLBit and SQLDate are used as modifiers to return strings for dynamic SQL preventing any potential SQL injection attacks.

UpdateValueSwitch simply sets a return value dependant on the true or false provided, with the d (default) value overriding the p (postback) value when the p value is blank.

Set an asp:TextBox value to a number

MyTextbox.Text = ClearDou(UpdateValueSwitch(IsPostBack,dr.Item(1).ToString, GetPostBackValue(Request,MyTextbox)))

Pull a date from an asp:TextBox and update SQL

Dim u As String = SQLDate(GetPostBackDate(Request, TextBoxDate))Using mi As New SqlConnection(str)    mi.Open()    Using com As New SqlCommand("EXEC [UpdSproc] " + u + "", mi)        com.ExecuteNonQuery()    End UsingEnd Using