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DataBinding errors with interfaces
private object FormatObject(object value)
if (this.ControlAtDesignTime())
return value;
System.Type propertyType = this.propInfo.PropertyType;
if (this.formattingEnabled)
ConvertEventArgs cevent = new ConvertEventArgs(value, propertyType);
if (cevent.Value != value)
return cevent.Value;
TypeConverter sourceConverter = (TypeConverter) null;
if (this.bindToObject.FieldInfo != null)
sourceConverter = this.bindToObject.FieldInfo.Converter;
return Formatter.FormatObject(value, propertyType, sourceConverter, this.propInfoConverter, this.formatString, this.formatInfo, this.nullValue, this.dsNullValue);
ConvertEventArgs cevent = new ConvertEventArgs(value, propertyType);
object obj1 = cevent.Value;
if (propertyType == typeof (object))
return value;
if (obj1 != null && (obj1.GetType().IsSubclassOf(propertyType) || obj1.GetType() == propertyType))
return obj1;
TypeConverter converter = TypeDescriptor.GetConverter(value != null ? value.GetType() : typeof (object));
if (converter != null && converter.CanConvertTo(propertyType))
return converter.ConvertTo(value, propertyType);
if (value is IConvertible)
object obj2 = Convert.ChangeType(value, propertyType, (IFormatProvider) CultureInfo.CurrentCulture);
if (obj2 != null && (obj2.GetType().IsSubclassOf(propertyType) || obj2.GetType() == propertyType))
return obj2;
throw new FormatException(System.Windows.Forms.SR.GetString("ListBindingFormatFailed"));
to use with LINQPad :
add reference to the following:
void Main()
MyForm viewBase = new MyForm { Text = "Base" }, viewDerived = new MyForm { Text = "Derived" };
var viewModel = new MyViewModel();
viewBase.DataBindings.Add("Base", viewModel, "Base", false, DataSourceUpdateMode.OnPropertyChanged);
viewDerived.DataBindings.Add("Derived", viewModel, "Derived", false, DataSourceUpdateMode.OnPropertyChanged);
// Define other methods and classes here
interface IBase {
string BaseMethod();
interface IDerived : IBase {
string DerivedMethod();
class Base: IBase {
public string BaseMethod() {return "BaseMethod"; }
class Derived : Base, IDerived {
public string DerivedMethod(){return "DerivedMethod"; }
class DerivedConverter : TypeConverter {
private readonly Type typeD = typeof(Derived);
public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType) {
if (destinationType.IsAssignableFrom(typeD)) return true;
return base.CanConvertFrom(context, destinationType);
public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture,
object value, Type destinationType) {
if (destinationType.IsAssignableFrom(typeD)) return value;
return base.ConvertTo(context, culture, value, destinationType);
class MyForm : Form {
public IBase Base { get; set; }
public IDerived Derived { get ; set; }
protected override void OnLoad(EventArgs e) {
(Base == null ? "Base is null" : Base.BaseMethod()).Dump("MyForm." + this.Text);
(Derived == null ? "Derived is null" : Derived.DerivedMethod()).Dump("MyForm." + this.Text);
class MyViewModel {
public IBase Base { get { return new Base(); } }
public IDerived Derived { get { return new Derived(); } }
Full stack trace:
System.FormatException: Cannot format the value to the desired type.
at System.Windows.Forms.Binding.FormatObject(Object value)
at System.Windows.Forms.Binding.PushData(Boolean force)
at System.Windows.Forms.Binding.UpdateIsBinding()
at System.Windows.Forms.Binding.CheckBinding()
at System.Windows.Forms.Binding.SetListManager(BindingManagerBase bindingManagerBase)
at System.Windows.Forms.ListManagerBindingsCollection.AddCore(Binding dataBinding)
at System.Windows.Forms.BindingsCollection.Add(Binding binding)
at System.Windows.Forms.BindingContext.UpdateBinding(BindingContext newBindingContext, Binding binding)
at System.Windows.Forms.Control.UpdateBindings()
at System.Windows.Forms.Control.OnBindingContextChanged(EventArgs e)
at System.Windows.Forms.Control.set_BindingContextInternal(BindingContext value)
at System.Windows.Forms.ContainerControl.set_BindingContext(BindingContext value)
at System.Windows.Forms.ContainerControl.get_BindingContext()
at System.Windows.Forms.Control.UpdateBindings()
at System.Windows.Forms.Control.OnBindingContextChanged(EventArgs e)
at System.Windows.Forms.ContainerControl.OnCreateControl()
at System.Windows.Forms.Form.OnCreateControl()
at System.Windows.Forms.Control.CreateControl(Boolean fIgnoreVisible)
at System.Windows.Forms.Control.CreateControl()
at System.Windows.Forms.Control.WmShowWindow(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
at System.Windows.Forms.Form.WmShowWindow(Message& m)
at System.Windows.Forms.Form.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
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