Setting object property by reflection

  • Thread starter Thread starter Omikron
  • Start date Start date
O

Omikron

Hi
I would like to set a property of an object (like Web UI control)
based on the property name to given value (as string.)

I have:


Dim obj_FinalProperty As System.Reflection.PropertyInfo =
obj_ref.GetType().GetProperty(PropertyName)

Dim obj_MethodInfo As MethodInfo =
obj_FinalProperty.GetSetMethod(True)
obj_MethodInfo.Invoke(obj_ref, Value)


obj_ref is the control reference. Now let's say I have a button and I
want to set its "Height" to "20" (provided as string). Height property
is System.Web.UI.WebControls.Unit, and I am getting exception when it
comes to Invoke call:

Object of type 'System.String' cannot be converted to type
'System.Web.UI.WebControls.Unit'. I don't know why this happens,
because when I write directly - button.Height = "20" everything is
fine. How can I overcome this problem ?

Many Thanks
Bartek
 
Omikron said:
Hi
I would like to set a property of an object (like Web UI control)
based on the property name to given value (as string.)

I have:


Dim obj_FinalProperty As System.Reflection.PropertyInfo =
obj_ref.GetType().GetProperty(PropertyName)

Dim obj_MethodInfo As MethodInfo =
obj_FinalProperty.GetSetMethod(True)
obj_MethodInfo.Invoke(obj_ref, Value)
Click to expand...
There's no need to call .GetSetMethod(); you can call .SetValue() directly.
obj_ref is the control reference. Now let's say I have a button and I
want to set its "Height" to "20" (provided as string). Height property
is System.Web.UI.WebControls.Unit, and I am getting exception when it
comes to Invoke call:

Object of type 'System.String' cannot be converted to type
'System.Web.UI.WebControls.Unit'. I don't know why this happens,
because when I write directly - button.Height = "20" everything is
fine. How can I overcome this problem ?
Click to expand...
Visual Basic supports some convenient implicit conversions that reflected
properties don't. You need to supply a value of the exact same type as the
property, not merely one that's convertible to it. You can do this by
calling Convert.ChangeType() and supplying the property's type.
 
Visual Basic supports some convenient implicit conversions that reflected
properties don't. You need to supply a value of the exact same type as the
property, not merely one that's convertible to it. You can do this by
calling Convert.ChangeType() and supplying the property's type.
Click to expand...

I tried this before as well. I had:

Dim obj_FinalProperty As System.Reflection.PropertyInfo =
obj_Control.GetType().GetProperty(PropertyName)

If Not obj_FinalProperty Is Nothing AndAlso
obj_FinalProperty.CanWrite = True Then
Try
Dim ValueType As Type =
System.Type.GetType(obj_FinalProperty.PropertyType.AssemblyQualifiedName.ToString(),
False, True)

If Not ValueType Is Nothing Then
obj_FinalProperty.SetValue(obj_Control,
System.Convert.ChangeType(Value, ValueType), Nothing)
End If

Still Convert.ChangeType returns exception about invalid conversion.
So I understand there is no way to apply string value to Unit type by
the reflection ?
 
Ok, I think I find a solution. I need to check if the type implements
Parse method, if so I can invoke it.
 
Omikron said:
I tried this before as well. I had:

Dim obj_FinalProperty As System.Reflection.PropertyInfo =
obj_Control.GetType().GetProperty(PropertyName)

If Not obj_FinalProperty Is Nothing AndAlso
obj_FinalProperty.CanWrite = True Then
Try
Dim ValueType As Type =
System.Type.GetType(obj_FinalProperty.PropertyType.AssemblyQualifiedName.ToString(),
False, True)
Click to expand...
What on earth is this supposed to achieve? Just stop at .PropertyType.
If Not ValueType Is Nothing Then
obj_FinalProperty.SetValue(obj_Control,
System.Convert.ChangeType(Value, ValueType), Nothing)
End If
Click to expand...
ValueType cannot possibly be Nothing. The property must have a type and it
must be accessible, otherwise you wouldn't have been able to get it at all.
Still Convert.ChangeType returns exception about invalid conversion.
Click to expand...

Yes, I should have dug further. Convert only operates on system types. You
want TypeConverter here.
So I understand there is no way to apply string value to Unit type by
the reflection ?
Click to expand...

Yes, there is. Here's a full snippet:

Dim PropertyInfo As PropertyInfo =
obj_Control.GetType().GetProperty(PropertyName)
If PropertyInfo Is Nothing Then Throw New
InvalidOperationException(String.Format("Property '{0}' does not exist.",
PropertyName))
If Not PropertyInfo.CanWrite Then Throw New
InvalidOperationException(String.Format("Property '{0}' is not writable.",
PropertyName))
PropertyInfo.SetValue(obj_Control,
TypeDescriptor.GetConverter(PropertyInfo.PropertyType).ConvertFromString(Value),
Nothing)
 
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