Archive for April, 2008

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Find GridView Column Index With AccessibleHeaderText

Trying to access a specific GridView’s column is especially easy, but only if you know the column index. One way to handle accessing the column is to hard code the column index into the code:

GridView gv = new GridView();
DataControlField dcf = gv.Columns[5];

The main problem with the above solution is if you add a new column at index 1, you will need to manually change all hardcoded indexes. Therefore, another way to handle this is to set a constant integer for each column containing the index.

const int _MYCOLUMN = 5;
GridView gv = new GridView();
DataControlField dcf = gv.Columns[5];

Using this would only require you to change the _MYCOLUMN constant integer in one location, which would reflect in the rest of your code. However, an even better way to handle this is to access the column by a defined name. The method below involves setting the AccessibleHeaderText of a column on the aspx page when the gridview column is defined.

<asp:GridView ID=”GridView1″ runat=”server” AutoGenerateColumns=”False”>
<Columns>
<asp:BoundField AccessibleHeaderText=”date” DataField=”date” HeaderText=”Date” SortExpression=”date” />
<asp:BoundField AccessibleHeaderText=”article” DataField=”article” HeaderText=”Article” SortExpression=”article” />
</Columns>
</asp:GridView>

By setting the AccessibleHeaderText, we can now access the column through this header name. The function below requires the gridview and a string containing the AccessibleHeaderText. The function will return the index of the column, if found . Otherwise, negative one (-1).

private int findColumnIndex(GridView gridView, string accessibleHeaderText)
{
for (int index = 0; index < gridView.Columns.Count; index++)
{
if (String.Compare(gridView.Columns[index].AccessibleHeaderText, accessibleHeaderText, true) == 0)
return index;
}
return -1;
}

By using this method, adding a new column in index one will not affect the rest of the code. The method checks the AccessibleHeaderText of each column to verify that it matches your specified string. If it matches, it returns the index.

int dateIndex = findColumnIndex(GridView1, “date”);
int authorIndex = findColumnIndex(GridView1, “author”);
int articleIndex = findColumnIndex(GridView1, “article”);

In the above example, dateIndex will return 0, authorIndex will return -1, and articleIndex will return 1. It’s as simple as that!

Posted under C# by Victor Chen - No Comments

Submit Form On Enter Key Solution

It is natural for web users to hit the enter key to submit a form or otherwise activate an action. There have been several cases where the form does not submit on the enter key. The below example works.

<body>
<form id=”form1″ runat=”server”>
<div>
<asp:TextBox ID=”txtFirstName” runat=”server”></asp:TextBox>
<asp:Button ID=”Button1″ runat=”server” Text=”Button” onclick=”Button1_Click” />
<asp:Label ID=”lblOutput” runat=”server” Text=”"></asp:Label>
</div>
</form>
</body>

The Button1_Click action simply copies the input text from txtFirstName into the label lblOutput. Because this simple example works, one would expect this to work in every case. That is not the case. If hitting the enter key does not submit the form, try one of the following below:

  1. Try putting an invisible HTML Input (Submit) button. Though this has worked for others, it did not work for my situation.

    <input type=”text” style=”display:none”/>

  2. A second option to try is to use a onKeyDown event. This second option will append a moderately long javascript script to check for the enter key on each button press. If the button is pressed, it activates the form submit. To use this, place this script in the head. Finally, on the last input textbox, use the following:

    onKeyPress=”return submitFormWithEnter(this,event)”

    The script is below goes in the within html head tags:

    <script type=”text/javascript”>

    function submitFormWithEnter(myfield,e)
    {
    var keycode;
    if (window.event) keycode = window.event.keyCode;
    else if (e) keycode = e.which;
    else return true;

    if (keycode == 13)
    {
    myfield.form.submit();
    return false;
    }
    else
    return true;
    }
    </script>

  3. This last situation, which worked best for me also checks for the enter key using javascript, but instead of simply activating the form’s action, the function to be run is directly specified. Below, EmailTextBox is the last input TextBox element. Next, replace LoginButton with the ASP Submit Buttton. This script needs to go in the Page_Load section of the codebehind.

    EmailTextBox.Attributes.Add(”onKeyPress”, “javascript:if (event.keyCode == 13) __doPostBack(’” + LoginButton.UniqueID + “‘,”)”);

Posted under C#, Javascript by Victor Chen - No Comments

Using The At Symbol (@) With Strings

Defining the @ symbol prior to the assigning a string value will prevent the need for doubling the backslash (\) in C#. The at symbol (@) simply ignores escape characters. This is useful when accessing a directory local to the server. For example, you may want to store the local directory path in a string. Without using the at symbol (@), it would look similar to the following:

string directoryPath = “C:\\uploadedFiles\\pdfs”;

Note that in the above example, each backslash is needs to be doubled. However, with the at symbol (@), it is both easier to read and type because we can keep the original single backslash format.

string directoryPath = @“C:\uploadedFiles\pdfs”;

Just another trick in C# that may not be blatantly obvious, but very useful. Note that using the at symbol (@) can can be used sparing as in the demonstrated example below:

string directoryPath = “C:\\uploadedFiles” + @“\pdfs”;

In the example above, the at symbol (@) was not used in the first half, but was used in the second half. Not sure why you would use this third example in this case, but just remember that it is an option.

Posted under C# by Victor Chen - No Comments
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