ASP.NET Tips & Web Development
Generating Random Colors in VB.NET
Jun 16th
Here’s how to generate a random color in the hex RGB format “#FFFFFF”.
Firstly, we generate random integer values from 0 to 255 for each color channel, red, green and blue:
Dim RandomClass As New Random()
Dim intR, intG, intB As Integer
intR = RandomClass.Next(0, 256)
intG = RandomClass.Next(0, 256)
intB = RandomClass.Next(0, 256)
Dim intR, intG, intB As Integer
intR = RandomClass.Next(0, 256)
intG = RandomClass.Next(0, 256)
intB = RandomClass.Next(0, 256)
With random numbers you need to give two values. The range returned is greater than or equal to the first value and less than the second value so (0, 256) gives a range from 0 to 255 inclusive.
Next, we convert these integer values to hexadecimal:
Dim hexR, hexG, hexB, As String
hexR = intR.ToString(“X”).PadLeft(2, “0″c)
hexG = intG.ToString(“X”).PadLeft(2, “0″c)
hexB = intB.ToString(“X”).PadLeft(2, “0″c)
hexR = intR.ToString(“X”).PadLeft(2, “0″c)
hexG = intG.ToString(“X”).PadLeft(2, “0″c)
hexB = intB.ToString(“X”).PadLeft(2, “0″c)
The ToString(“X”) puts the integer into hexadecimal format. The PadLeft(2, “0″c) adds a leading zero before single character hex values, numbers 0-15 so that value 8 becomes 08. Expressing a color hex RGB value shorter than 6 digits may cause problems.
Finally, we put the red, green and blue values together with a hash symbol in a string:
Dim strColor As String
strColor = “#” & hexR & hexG & hexB
strColor = “#” & hexR & hexG & hexB
You can then use this string value to generate random colors within your application.
To set the random color for web form controls you can generally use the randomly generated integer values rather than the hex format, like this:
Label1.BackColor = Drawing.Color.FromArgb(intR, intG, intB)
(2 votes, average: 5.00 out of 5)
Loading ...Selecting a random database record with SQL
Apr 9th
Here’s a “quick and dirty” way of selecting a database record at random. This can be used for things like showing a featured product or a random advert.
Here’s the SQL to use in your SelectCommand:
SELECT TOP 1 * FROM table ORDER BY NEWID()
You can either bind a control such as a Repeater to the data source or use VB to pull data from the record and use it. Here’s an example of producing a random link in a page. ASP.NET form:
<asp:HyperLink ID=”lnkRandomProduct” runat=”server” />
And here’s the VB to grab the data for the single record:
Dim dv As Data.DataView
dv = CType(srcRandomCourse.Select(DataSourceSelectArguments.Empty), Data.DataView)
Dim dr As Data.DataRowView = dv(0)
Dim strProductName As String = CStr(dr(“product_name”))
Dim strProductId As String = CStr(dr(“product_id”))
dv = CType(srcRandomCourse.Select(DataSourceSelectArguments.Empty), Data.DataView)
Dim dr As Data.DataRowView = dv(0)
Dim strProductName As String = CStr(dr(“product_name”))
Dim strProductId As String = CStr(dr(“product_id”))
lnkRandomProduct.Text = strProductName
lnkRandomProduct.NavigateUrl = “http://www.yoursite.com/products.aspx?id=” & strProductId
(3 votes, average: 5.00 out of 5) Loading ...Calculating Age from Date of Birth in VB.NET
Mar 8th
It’s quite common to need to calculate a person’s age from the date of birth they have entered. Here’s the quick and easy way of doing it:
Dim strDOB As String
strDOB = txtDateOfBirth.Text
strDOB = txtDateOfBirth.Text
Dim intAge As Integer
intAge = Math.Floor(DateDiff(DateInterval.Month, DateValue(strDOB), Now()) / 12)
lblAge.Text = intAge
In this example the date of birth data is captured in a TextBox control called txtDateOfBirth. The DateDiff function calculates the difference between two dates. The arguments are the interval to focus on (here months), the first date (here the date of birth) and the second date (here the current date). The date of birth is expressed as DateValue(strDOB) to convert the string to a date format. This is then divided by 12 to give the age in years as a decimal. Finally, the introductory Math.Floor is used to round the number down to the nearest whole number.
(3 votes, average: 5.00 out of 5) Loading ...Conditional Formatting in a GridView
Dec 17th
This code will allow you to change the background colour of a cell or entire row depending on certain conditions.
In this example we test if the row being bound is a data row, then if the second column (indexed as 1) is equal to 0. If it is then the row’s backcolor is set as PeachPuff and the cell itself has backcolor Salmon. Remember that cell indexing starts at 0 so that the first column is e.Row.Cells(0), the second column e.Row.Cells(1), etc.
Protected Sub grdTable_RowDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles grdTable.RowDataBound
If e.Row.RowType = DataControlRowType.DataRow Then
If e.Row.Cells(1).Text = “0″ Then
e.Row.BackColor = System.Drawing.Color.PeachPuff
e.Row.Cells(1).BackColor = Drawing.Color.Salmon
End If
End If
End Sub
To change the text colour simply substitute BackColor with ForeColor.
(3 votes, average: 5.00 out of 5) Loading ...Returning a Record Count using VB.net
Dec 15th
When websites feature a text search and a table or list of results you will sometimes see something like:
73 records matched your search or 128 matches found.
This is actually very easy to do but incredibly hard to find an easy way of doing it. Here’s how it’s done.
This example is based on searching a company contact list.
Firstly, in your web form you need your DataSource and SelectCommand, for example:
<asp:SqlDataSource ID=”srcResults” runat=”server” ConnectionString=”<%$ ConnectionStrings:constrConnectionString %>” SelectCommand=”SELECT * FROM [contacts] WHERE [firstname] LIKE ‘%’ + txtSearch + ‘%’ OR [lastname] LIKE ‘%’ + txtSearch + ‘%’”>
Then, in your VB you get the number of records returned as follows:
Dim intMatches As Integer
Dim dv As Data.DataView
dv = CType(srcResults.Select(DataSourceSelectArguments.Empty), Data.DataView)
intMatches = dv.Count.ToString()
Dim dv As Data.DataView
dv = CType(srcResults.Select(DataSourceSelectArguments.Empty), Data.DataView)
intMatches = dv.Count.ToString()
You will need to change srcResults in the third line to the ID of your DataSource control, the rest of the code can stay as it is.
Finally, you need to output the number of records to the page. This can be done by putting a Literal or Label control in the web form:
<asp:Literal ID=”litRecordCountText” runat=”server” />
Here’s some code which gives different output depending on whether there are 0, 1 or more than 1 record counted:
If intMatches = 0 Then
litRecordCountText.Text = “<span style=’color:’cc0000′>Sorry, no contacts matched your search text.<br />Try entering just the first few letters of a name.</span>”
ElseIf intMatches = 1 Then
litRecordCountText.Text = “1 match found. The following contact matches your search.”
Else
litRecordCountText.Text = intMatches & ” matches found. The following contacts match your search.”
End If
litRecordCountText.Text = “<span style=’color:’cc0000′>Sorry, no contacts matched your search text.<br />Try entering just the first few letters of a name.</span>”
ElseIf intMatches = 1 Then
litRecordCountText.Text = “1 match found. The following contact matches your search.”
Else
litRecordCountText.Text = intMatches & ” matches found. The following contacts match your search.”
End If
(3 votes, average: 5.00 out of 5) Loading ...
