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.NET Forum / Windows Forms / WinForm Data Binding / November 2005DataGridViewComboBoxColumn where ValueMember is bind to property which type is Guid = ERROR
I have Custom Collection with Custom Object which has Guid as Id - I bind DataGridView into it and it works BUT if I make one Column as DataGridViewComboBoxColumn the trouble becomes. If the DataGridViewComboBoxColumn ValueMember property type is Guid I get nice error when I try to insert a new row in DataGridView. The following exception occurred in the DataGridView: System.ArgumentException: DataGridViewComboBoxCell value is not valid. To replace this default dialog please handle the DataError event. If I suppress this event with custom DataError event I see the problem, DataGridView cannot insert selected value from the DataGridViewComboBoxColumn at all. BUT this problem goes a way if DataGridViewComboBoxColumn ValueMember bind property type is String... ok, no Guid but String is okay - problem is that I would like to have Id's as Guid on my custom objects or I need to make those String and add logic on properties to check that the String is actually valid Guid... not good. Also if I try this with DataSet / DataTable I don't have any problems even that DataGridViewComboBoxColumn ValueMember bind property type is Guid, Int, String or what ever... so is this a bug (don't think so), or (more likely) I'm missing some properties / methods from interfaces I need to implement to make this work? Regards, Oka Morikawa D I G I N E Hi, >I have Custom Collection with Custom Object which has Guid as Id - I bind >DataGridView into it and it works BUT if I make one Column as [quoted text clipped - 20 lines] > likely) I'm missing some properties / methods from interfaces I need to > implement to make this work? A string is a reference type while a Guid is a value type. When a property type is a reference type then it can return null, when it is a value type it can't return null, at the best it can return the default initialized value. So if the grid (indireclty) adds a new custom object, then your key (Guid) isn't null but {0000000-000....} instead and because that guid doesn't exists in the ComboBox it crashes. Untyped DataTable's don't have this problem since all property types are object, and so they can return DBNull.Value or a boxed Guid. In VS2005 final release you can use the new nullable type support & syntax: public class CustomObject { private Guid? someKey = null; // now this property can return null (eg. as default for new objects) or a Guid public Guid? SomeKey { get { return someKey; } set { someKey = value; } } } (Note: This doesn't work with VC2005beta2, because of a boxing problem with nullable types) --- Another thing you can do, is make sure that newly created objects have a Guid that exists in the ComboBox. HTH, Greetings > Regards, > Oka Morikawa > D I G I N E Hi, I tried that and no go. Behaviour is little different thought, now I can select items from ComboBox (before it gave the exception immediately I insert new row into grid) but it cannot store the Id into that column and gives the same exception when I select item from ComboBox and go to next column. I think that ComboBox tries to insert that Id value as String NOT Guid and that's why it gives the exception? Any ideas to get workaround for this? I'm runnin VS2005RTM Regards, Oka Morikawa D I G I N E > Hi, > [quoted text clipped - 64 lines] >> Oka Morikawa >> D I G I N E Hi, > Hi, I tried that and no go. Behaviour is little different thought, now I > can select items from ComboBox (before it gave the exception immediately I [quoted text clipped - 4 lines] > I think that ComboBox tries to insert that Id value as String NOT Guid and > that's why it gives the exception? Any ideas to get workaround for this? I assume i tried something in the lines of what you are doing and it worked (though with nullable types). The editing worked too. Without seeing any code i have no idea why it doesn't work for you. If you want you can post all relevant code. HTH, Greetings > I'm runnin VS2005RTM > [quoted text clipped - 70 lines] >>> Oka Morikawa >>> D I G I N E Thanks, I tested also with bare minimum Custom Objects and it works. My Custom Objects inherits Base Objects where is some common logic and this seems to break something... I'll post later more about this - Thanks! Regards, Oka Morikawa D I G I N E > Hi, > [quoted text clipped - 90 lines] >>>> Oka Morikawa >>>> D I G I N E I found the bug and it's quite weird. I don't know how the DataGridView works internally but the problem was the custom objects list base object. I inherit all my custom collections from base class and the problem was in FindCore method: protected override bool SupportsSearchingCore { get { return true; } } protected override int FindCore(PropertyDescriptor prop, object key) { int result = -1; for (int i = 0; i < this.Count; i++) { object value = prop.GetValue(this.Items[i]); if (value.ToString() == key.ToString()) result = i; } return result; } the bug was in line: if (value.ToString() == key.ToString()) where it was originally without .ToString() method. Question is why DataGridView runs this FindCore method even that there is no such function going on in DGV? Also why DGV crash on that particular line since both value and key are object types what I'm comparing? Then I'm wondering if all this FindCore method will work with all types (object value = prop.GetValue(this.Items[i]);) I throw in or do I soon run into new bug? ...now it works but I'm afraid of my code since I don't know what I fixed and why. Regards, Oka Morikawa D I G I N E > Hi, > [quoted text clipped - 90 lines] >>>> Oka Morikawa >>>> D I G I N E Hi, >I found the bug and it's quite weird. I don't know how the DataGridView >works internally but the problem was the custom objects list base object. I [quoted text clipped - 31 lines] > new bug? ...now it works but I'm afraid of my code since I don't know what > I fixed and why. I don't think it is that strange it calls FindCore, at least not for the Custom List you have bound to the ComboBox. It uses that to find the right item based on the key in the datagrid. I think it originates from the following problem : int i = 10; object o = i; object p = i; Console.WriteLine( o == p ); //writes false It writes false, because each value type is boxed and has its own reference and therefore reference comparison fails. To be safe you should use: .... if ( object.Equals(value, key) ) result = i; .... HTH, Greetings > Regards, > Oka Morikawa [quoted text clipped - 94 lines] >>>>> Oka Morikawa >>>>> D I G I N E I just ran into this one as well. My fix was to remove the binding for the datagrid's datasource in the dispose. If you try to dispose the combobox column's datasource before unbinding it (which is what the components.dispose method is likely doing in your case), you will get that error. The below code fixed the problem for me. 'UserControl overrides dispose to clean up the component list. Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean) If disposing Then 'Following line is required to dispose of the comboboxcolumn properly DataGridView1.DataSource = Nothing If Not (components Is Nothing) Then components.Dispose() End If End If MyBase.Dispose(disposing) End Sub Jim Wooley www.devauthority.com/blogs/jwooley >I have Custom Collection with Custom Object which has Guid as Id - I bind >DataGridView into it and it works BUT if I make one Column as [quoted text clipped - 24 lines] > Oka Morikawa > D I G I N E Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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