BeginInvoke on PropertyInfo of Items property for ComboBox

Rightthen

13y2.9kVisual Basic .NET

Dear Fellows,

The below written code works when i try to take the items Collection

as a whole and then apply index to it. outside of BeginInvoke.

//propName = ComboBoxProperties.Items;

PropertyInfo comboItems = typeof(ComboBox).GetProperty( propName.ToString().Trim() ) ;

var a = comBox_.BeginInvoke(new Func<object, Object>(comboItems.GetValue), comBox_);

object c = null;

c = comBox_.EndInvoke(a);

retVal = (((ComboBox.ObjectCollection)c)[(int)propIndex]);

but when i try to apply index inside BeginInvoke itself it does not work gives an exception of

An unhandled exception of type 'System.Reflection.TargetInvocationException' occurred in mscorlib.dll

Additional information: Exception has been thrown by the target of an invocation.

i.e when i do like this

delegate object getItemDlg ( object comBox, object[] index );

PropertyInfo comboItems = typeof(ComboBox).GetProperty( propName.ToString().Trim() ) ; object[] index = { propIndex };

var a = comBox_.BeginInvoke( new getItemDlg(comboItems.GetValue), comBox_, index ); object c = null;

c = comBox_.EndInvoke(a);
retVal = c;

i have tried using Func<object,object[],object> and

var a = comBox_.BeginInvoke( new getItemDlg(comboItems.GetValue), new object[]{ comBox_, index });

but to no avail

specifically i would like to know how does one get indexed properties with begin invoke

Thanks

Regards

2 Replies

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Vulpes13y ago
Accepted answer
The problem is that a ComboBox doesn't actually have any indexed properties i.e. properties which are implemented using an indexer.

You might think that Items would be an indexed property but in fact it's just a normal 'named' property which returns a ComboBox.ObjectCollection.

So if you're just invoking PropertyInfo.GetValue, then the only way to do it is how you're doing it now.

FWIW, it would be possible to use a lambda expression which gets the actual item you want and then pass that to BeginInvoke:

PropertyInfo comboItems = typeof(ComboBox).GetProperty(propName.ToString().Trim());
Func func = (obj, index) => ((ComboBox.ObjectCollection)comboItems.GetValue(obj, null))[index];
var a = comBox_.BeginInvoke(func, new object[]{comBox_, (int)propIndex});
object c = null;
c = comBox_.EndInvoke(a);
retVal = c;
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Rightthen13y ago
Vulpes

I am very thankful for ur input.

Thanks
Regards
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