Scott Hanselman's ComputerZen.com

Scott, now that is just awesome! Not so much the tip of how to resize the columns, but the idea of how you came up with a better way to do it. All about the way we think and come up with good/simple code & solutions.

Great idea - thanks for sharing.

I thought you could set the Width property of a custom column style to -1 to achieve the same effect...

(2 minutes later) I just tried that and it doesn't work. Maybe I'm confusing this with the asp.net grid control...

Guess what you find if you look at ColAutoResize in Relector? Graphics.MeasureString. Most of the example tend to assume the DataSource is a DataTable, but tt works well with collections if you check for the IList or IListSource interface on the DataSource.

Awesome, Scott! That is a nice little snippet, even with Scott Allen's discovery. :)

That was a great example of how a developer should think. Of course I also don't have a comforing feeling when I know I'm using some unintended, private functionality, but the process of getting to the solution was perfect.
I want to be like you when I grow up :)

Agreed. And I also get your point that it's better to "illegally" use reflection than to go around measuring strings and duplicating work (possibly incorrectly) that's already done.

On a related note, I've always hated the ListView control in Windows. It should be much more intelligent than this when being resized. For example, when it grows beyond the last column in width, it just shows wasted blank space, even if some columns are too narrow for their content... I mean, we have web browsers doing a fine job laying out multiple levels of nested tables containing a mix of rich text and images, while desktop applications continue to use this relic from 15 years ago...

The new fancy layout stuff in VS 2005 might allow for a neat new list control. I guess I could try to make one, if I had a spare computer to install this "community preview" thing :).

I'm trying to convert this to vb (and I've never done reflection before) and I'm having a problem. Is this a correct implementation of your code or am I going a little wrong here?

Public Class DataGridButBetter
Inherits DataGrid
Public Sub AutoResizeColumns()
Try
Dim t As Type = MyBase.GetType 'also tried me.GetType but t always ends up as DataGridButBetter
Dim m As System.Reflection.MethodInfo = t.GetMethod("ColAutoResize", System.Reflection.BindingFlags.NonPublic) 'and this ends up as nothing (null to you c# boys)
For i As Integer = Me.FirstVisibleColumn To Me.VisibleColumnCount - 1
m.Invoke(Me, New Object() {i})
Next
Catch ex As Exception
System.Diagnostics.Trace.Write("Failed Resizing Columns: " + ex.ToString())
End Try
End Sub
End Class

any ideas where I'm going wrong? thanks!

Windows.Forms.DataGrid is what I'm doing this to.

Excellent demonstration on reflection for someone new to reflection! I seem to be having reflection security problems though. This is a WINFORM application and when I debug it t.GetMethod("ColAutoResize", System.Reflection.BindingFlags.NonPublic) returns null. Is there anything special that needs to be done before the CLR will allow visibilty to the private methods? Thanks!

Great Job. For the last couple questions about the GetMethod returning null, try this:

[VB.net]
Dim m As MethodInfo = t.GetMethod("ColAutoResize", BindingFlags.NonPublic Or BindingFlags.Instance)

[C#]
MethodInfo m = t.GetMethod("ColAutoResize", BindingFlags.NonPublic | BindingFlags.Instance)

Someone else can probably explain why this works better than I.

Cheers!

h McIntyre - aren't you really doing it to a 'DataGridButBetter' extension of the DataGrid?? I try the same thing in my extended DataGrid and get null as well, even with that last OR addition. I think it is because we aren't getting the correct type back for GetType - we are getting our DataGrids, not the WinForms DataGrid...

Any ideas???

I found, for whatever reason, that multiple queries to the VisibleColumnCount were not always the same...And it was stopping after 5 columns, regardless of how many were in the DataSet; however, the columns were there, and visible, just not being displayed.

[vb.net that's working great]
Private Sub sqlGrid_DataSourceChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles sqlGrid.DataSourceChanged
Try
Dim t As Type = sqlGrid.GetType
Dim m As Reflection.MethodInfo = t.GetMethod("ColAutoResize", Reflection.BindingFlags.NonPublic Or Reflection.BindingFlags.Instance)

Dim i As Integer = sqlGrid.FirstVisibleColumn
Dim j As Integer = sqlGrid.VisibleColumnCount
Do While i < j
m.Invoke(sqlGrid, New Object() {i})
i = i + 1
Loop
Catch ex As Exception
Trace.Write("Failed to resize column: " + ex.ToString + vbCrLf)
End Try
End Sub

Reflection works on a specific Type so what you want to do in the subclassed DataGrid scenario is grab the MethodInfo of ColAutoResize(int) off DataGrid and *not* the subclass. You also need to make sure you're specifying BindingFlags.Instance as well as the parameter signature. You then perform Invoke() on your subclassed instance. Here's what it might look like in a sub-classed SuperDataGrid:

public void AutoResizeColumns() {

MethodInfo m = typeof(DataGrid).GetMethod("ColAutoResize", BindingFlags.Instance | BindingFlags.NonPublic, null, new Type[] { typeof(Int32) }, null);

for (int i = this.FirstVisibleColumn; (i < this.VisibleColumnCount); i++) {
m.Invoke(this, new object[] {i});
}
}

I found the following to be required:

using System.Reflection;



protected void dataGrid1_DataSourceChanged(object sender, System.EventArgs e)

{

try

{

Type t = dataGrid1.GetType();

MethodInfo m = t.GetMethod("ColAutoResize",

BindingFlags.Instance | BindingFlags.NonPublic);



for (int i = dataGrid1.FirstVisibleColumn;

i < dataGrid1.VisibleColumnCount; i++)

m.Invoke(dataGrid1, new object[]{i});

}

catch (Exception ex)

{

System.Diagnostics.Trace.Write("Failed Resizing Columns: " + ex.ToString());

}

}



”You must specify Instance or Static along with Public or NonPublic or no members will be returned”; quote from http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfsystemreflectionbindingflagsclasstopic.asp

Great, really great job!

I have been searching for an answer for this for a while now, and I came across solutions of pages and pages of code.

This is simple and elegant.

Congratulations.

If it can be useful I modified the code like this, so I can use it from wherever in my project.

\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
Public Sub columns_autoresize(ByRef sqlGrid As DataGrid)

Try
Dim t As Type = sqlGrid.GetType
Dim m As Reflection.MethodInfo = t.GetMethod("ColAutoResize", Reflection.BindingFlags.NonPublic Or Reflection.BindingFlags.Instance)

Dim i As Integer = sqlGrid.FirstVisibleColumn
Dim j As Integer = sqlGrid.VisibleColumnCount
Do While i < j
m.Invoke(sqlGrid, New Object() {i})
i = i + 1
Loop
Catch ex As Exception
Trace.Write("Failed to resize column: " + ex.ToString + vbCrLf)
End Try
End Sub
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

Very usefull code! Great work.
Thanks to all.
Carlos.

I was using the following code (on Paint Event) to AutoSize Columns in my datagrid:


Code:

Type t = dgTC.DataSource.GetType();
MethodInfo m = t.GetMethod("ColAutoResize", BindingFlags.Instance | BindingFlags.NonPublic);
for (int i = dgTC.FirstVisibleColumn; (i< dgTC.VisibleColumnCount); i++)
{
m.Invoke(dgTC, new object[]{i});
}

But after adding custom tablestyle and column style I am getting following exception:

Code:

System.Reflection.TargetInvocationException: Exception has been thrown
by the target of an invocation.

---> System.InvalidOperationException: The '' DataGridColumnStyle cannot
be used because it is not associated with a Property or Column in the DataSource.

At: System.Windows.Forms.DataGridColumnStyle.CheckValidDataSource(CurrencyManager value)

At: System.Windows.Forms.DataGridColumnStyle.GetColumnValueAtRow
(CurrencyManager source, Int32 rowNum)
at System.Windows.Forms.DataGrid.ColAutoResize(Int32 col)
--- End of inner exception stack trace ---

at System.Reflection.RuntimeMethodInfo.InternalInvoke(Object obj,
BindingFlags invokeAttr, Binder binder, Object[] parameters,
CultureInfo culture, Boolean isBinderDefault, Assembly caller, Boolean
verifyAccess)

at System.Reflection.RuntimeMethodInfo.InternalInvoke(Object obj,
BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture,
Boolean verifyAccess)

at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags
invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters)
at TotalControl.frmDataEntry.AutoSizeDataGrid() in c:\documents and settings\
MyComp\my documents\visual studio
projects\totalcontrol\frmdataentry.cs:line 699


Can someone help me with this? Thanks a lot in advance.