Problem Generating Table

[palehorse]

Hello everyone,

I am trying to generate a table on my form with rows/cells. I can do this fine with response.write; however, I am trying to pull away from that. What I am using is this:

[color=#0000ff]Dim[/color] tr [color=#0000ff]As[/color] TableRow
[color=#0000ff]Dim[/color] td [color=#0000ff]As[/color] TableCell
[color=#0000ff]Dim[/color] tbl [color=#0000ff]As[/color] Table
[color=#0000ff]Dim[/color] ph[color=#0000ff]As[/color] PlaceHolder
 
[size=3][size=2]tr = [color=#0000ff]New[/color] TableRow[/size]
td = [color=#0000ff]New[/color] TableCell
td.Controls.Add([color=#0000ff]New[/color] LiteralControl("Hello World"))
td.Attributes.Add("style", "width:4px; color:steelblue; font-size:2;")
tr.Cells.Add(td)
tbl.Rows.Add(tr)
[size=3][size=2]ph.Controls.Add(tbl)[/size]

[/size]But this doesn't work. I get the following at tbl.Rows.Add(tr) What am I doing wrong?

Object reference not set to an instance of an object.

Also - if I set tbl = New Table, I get the same error at phfiles.controls.add(tbl)

[/size]

 

[jmcilhinney]

The code you have provided instatiates tr and td but not tbl or ph.

 

[palehorse]

sorry - I am pretty new at this stuff - I am not sure what you mean. Can you give me an example or something.

 

[jmcilhinney]

One of the most fundamental rules of Object Oriented Programming is that you must instantiate an object before you can use it. The following line:

[color=Blue]Dim[/color] tr [color=Blue]As[/color] TableRow

declares the variable tr as being of type TableRow. At this point, it is not actually a TableRow but only a place that a TableRow can be stored. The following line:

tr = [color=Blue]New[/color] TableRow

creates an instance of, or instantiates, the TableRow class and assigns it to tr. You can declare and instantiate a variable in one line like so:

[color=Blue]Dim[/color] tr [color=Blue]As New[/color] TableRow

In your code, you have created a New TableRow and a New TableCell, but not a New Table or PlaceHolder. This means that you cannot legally use the tbl or ph variables as they do not refer to actual objects. You must instantiate them first:

tbl = [color=Blue]New[/color] Table
tbl.Rows.Add(tr)
ph = [color=Blue]New[/color] PlaceHolder
ph.Controls.Add(tbl)

 

[palehorse]

Alright - that made sense about what you said - I have fixed that now. I just can't seem to get anything to display on my screen - meaning, it doesn't appear to be generating my table. I have the following...btw, this is in the Page Load event...

[color=blue]Dim[/color] tbl [color=blue]As[/color] [color=blue]New [/color]Table
[color=blue]Dim[/color] tr [color=blue]As[/color] [color=blue]New[/color] TableRow
[color=blue]Dim[/color] td [color=blue]As[/color] [color=blue]New[/color] TableCell
[color=blue]Dim[/color] ph [color=blue]As[/color] [color=blue]New[/color] PlaceHolder
 
td.Controls.Add([color=#0000ff]New[/color] LiteralControl("Hello World"))
[size=3][size=2]td.Attributes.Add("style", "width:4px; color:steelblue; font-size:2;")[/size]
[size=2]tr.Cells.Add(td)
tbl.Rows.Add(tr)
[/size][size=3][size=2]ph.Controls.Add(tbl)[/size][/size][/size]

...and I no longer get an error - but I just get a blank page. What am I missing here?

 

[palehorse]

Ok, I have progressed a little bit...

If I first create my Table on the Webform - then go into my Page-Load event and code:

[color=#0000ff]Dim[/color] tr [color=#0000ff]As[/color] [color=#0000ff]New[/color] TableRow
[color=#0000ff]Dim[/color] td [color=#0000ff]As[/color] [color=#0000ff]New[/color] TableCell
td.Controls.Add([color=#0000ff]New[/color] LiteralControl("Hello World"))
[color=#008000]'td.Attributes.Add("style", "width:4px; color:steelblue; font-size:2;")[/color]
tr.Cells.Add(td)
[size=3][size=2]Table1.Rows.Add(tr)[/size][/size]
[size=3][size=2]

[/size][/size]
This will add the text "Hello World" in the cell. If I uncomment the td.attributes.add - then all I get is a blank page. What I was trying to do is, without first creating a table, dynamically generate a table on the page load event and set the proper attributes for the cells - I just can't seem to figure it out.

 

[jmcilhinney]

I've done next to no WebForms development I'm afraid, so I'll have to leave it up to others from here.