Workaround: this.radChat1.ChatElement.InputTextBox.TextBoxItem.TextBoxControl.Multiline = true; this.radChat1.ChatElement.InputTextBox.ButtonsStack.Children.Remove(this.radChat1.ChatElement.ShowToolbarButtonElement); this.radChat1.ChatElement.InputTextBox.ButtonsStack.Children.Remove(this.radChat1.ChatElement.SendButtonElement); StackLayoutElement stack = new StackLayoutElement(); stack.MinSize = new Size(0, 60); this.radChat1.ChatElement.InputTextBox.Parent.Children.Add(stack); this.radChat1.ChatElement.InputTextBox.Parent.Children.Remove(this.radChat1.ChatElement.InputTextBox); stack.StretchHorizontally = true; stack.Orientation = Orientation.Horizontal; stack.Children.Add(this.radChat1.ChatElement.InputTextBox); stack.Children.Add(this.radChat1.ChatElement.ShowToolbarButtonElement); stack.Children.Add(this.radChat1.ChatElement.SendButtonElement); this.radChat1.ChatElement.ShowToolbarButtonElement.StretchHorizontally = false; this.radChat1.ChatElement.SendButtonElement.StretchHorizontally = false;