Array of Checkboxes or Checkboxes in a PlaceHolder

Question

Hi Folks This is my first post here. If this is not the correct forum to post do accept my apologies. I am working on creating checkboxes dynamically. I have a stored procedure that reads a list of interests from a table and these have to be displayed as checkboxes. I do this using a place holder and what I get is a series of checkboxes with column name next to them but I want the values in that column and not column name. for(int i = 0; i < myDS.Tables[Interests].Rows.Count; i++) { CheckBox objCheckBox = new CheckBox(); objCheckBox.ID = myDS.Tables[Interests].Columns[InterestTypeID].ToString(); objCheckBox.Text = myDS.Tables[Interests].Columns[InterestType].ToString(); phlInterests.Controls.Add(objCheckBox); } If I create an array of checkboxes I keep running into an error Object reference not set to an instance of an object. Could someone point me in the right direction. Thanks Priya

pria525 · Answer

Thanks!! It works now. My next step is to get the selected values. Thanks again Priya

jshepler · Answer

Sorry that should be: cblInterests.DataValueField = InterestTypeID;

jshepler · Answer

As Simon pointed out you cannot use .ToString() from the Columns property: myDS.Tables[Interests].Columns[InterestType].ToString(); is invalid and is probably while you are getting the error. Besides what you are trying to do is get the column name (InterestType) which you already know so even if your line of code was valid it's redundant. You can just speciy the column name as a string like: private void createInterests() { DataSet myDS = new DataSet(); myDS = mytFinder.getTrailInterests(); cblInterests.DataSource = myDS.Tables[Interests].DefaultView; cblInterests.DataTextField = InterestType; cblInterests.DataValueField = Interests; cblInterests.DataBind(); }

pria525 · Answer

private void Page_Load(object sender System.EventArgs e) { // Put user code to initialize the page here if(!Page.IsPostBack) { this.createInterests(); } } private void createInterests() { DataSet myDS = new DataSet(); myDS = mytFinder.getTrailInterests(); cblInterests.DataSource = myDS.Tables[Interests].DefaultView; cblInterests.DataTextField = myDS.Tables[Interests].Columns[InterestType].ToString(); cblInterests.DataValueField = myDS.Tables[Interests].Columns[InterestsTypeID].ToString(); cblInterests.DataBind(); } mytFinder.getTrailInterests() -- this is the function for getting data from database and it works fine as I populate a dropdown list using the same function. Thanks a lot I really appreciate your help.

jshepler · Answer

Can you post your code and point out where the error is occuring?

pria525 · Answer

Hi jshepler Thanks for the info I tried it but it doesnt want to work. I am developing a custom module for DotNetNuke and I just keep getting this error Object Reference Not set to and instance of the object. Is there anything else that I have to do other than what you asked me to? Thanks

jshepler · Answer

If you don't specifically require a placeholder consider using the CheckBoxList control instead. You'll save yourself a lot of grief trying to get the selected values after a postback (submit). In your HTML you would have (instead of the placeholder): In your code you would have: void Page_Load (object sender EventArgs e) { if (!IsPostBack) { cblInterests.DataSource = msDS.Tables[Interests].DefaultView; cblInterests.DataTextField = InterestType; cblInterests.DataValueField = InterestTypeID; cblInterests.DataBind(); } } This will generate a checkbox for each row in your dataset. The values are pulled from InterestTypeID and the text (label) is pulled from InterestType. The biggest reason for doing it this way instead of manually adding the items is getting the selected value(s) later. Dynamically adding the controls the way you were doing does not keep them in the VIEWSTATE and hence will not be available on the form's postback. In other words when your user selects an item and clicks the submit button your code will no longer know anything about the checkboxes you put inside phlInterests - in fact they won't even exist anymore. If you absolutely must add the checkboxes manually like you posted there are pretty ugly ways of dealing with it that I could show you. Using the CheckBoxList control avoids all that mess. It will be added to the VIEWSTATE so it will be available on postbacks. You can access the selected values by looping through the contol's Items property and checking the Selected property of each item: foreach(ListItem item in cblInterests.Items) { if(item.Selected == true) { // code that does whatever you need with the selected item(s) // item.Value would be the InterestTypeID as a string // item.Text would be the InterestType as a string } }

shimtanny · Answer

Hi The problem is that you access a specified (by the name) column with the following: objCheckBox.ID = myDS.Tables[Interests].Columns[InterestTypeID].ToString(); Additionaly the ToString() method is not provided to return the columns values. // Solution: There are (maybe) several rows in your table. The columns specifies only the structure. If you wannt to read out values stored in a row you have to say at which position. For the elements of the row you have to specifiy the column... the position in the row. Try this: for(int i = 0; i < myDS.Tables[Interests].Rows.Count; i++) { CheckBox objCheckBox = new CheckBox(); DataRow dr = myDS.Tables[Interests].Rows[0]; objCheckBox.ID = (string) dr[InterestTypeID]; // cast into the stored object type. objCheckBox.Text = (string) dr[InterestType]; // cast into the stored object type. this.Controls.Add(objCheckBox); } Let me know if this is working. Cheers Simon