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---
title: "Troubleshooting Hybrid Applications"
ms.date: "03/30/2017"
helpviewer_keywords:
- "overlapping controls [WPF]"
- "Windows Forms [WPF], interoperability with"
- "Windows Forms [WPF], WPF interoperation"
- "interoperability [WPF], Windows Forms"
- "hybrid applications [WPF interoperability]"
- "message loops [WPF]"
ms.assetid: f440c23f-fa5d-4d5a-852f-ba61150e6405
---
# Troubleshooting Hybrid Applications
<a name="introduction"></a> This topic lists some common problems that can occur when authoring hybrid applications, which use both [!INCLUDE[TLA2#tla_winclient](../../../includes/tla2sharptla-winclient-md.md)] and Windows Forms technologies.
<a name="overlapping_controls"></a>
## Overlapping Controls
Controls may not overlap as you would expect. Windows Forms uses a separate HWND for each control. [!INCLUDE[TLA2#tla_winclient](../../../includes/tla2sharptla-winclient-md.md)] uses one HWND for all content on a page. This implementation difference causes unexpected overlapping behaviors.
A Windows Forms control hosted in [!INCLUDE[TLA2#tla_winclient](../../../includes/tla2sharptla-winclient-md.md)] always appears on top of the [!INCLUDE[TLA2#tla_winclient](../../../includes/tla2sharptla-winclient-md.md)] content.
[!INCLUDE[TLA2#tla_winclient](../../../includes/tla2sharptla-winclient-md.md)] content hosted in an <xref:System.Windows.Forms.Integration.ElementHost> control appears at the z-order of the <xref:System.Windows.Forms.Integration.ElementHost> control. It is possible to overlap <xref:System.Windows.Forms.Integration.ElementHost> controls, but the hosted [!INCLUDE[TLA2#tla_winclient](../../../includes/tla2sharptla-winclient-md.md)] content does not combine or interact.
<a name="child_property"></a>
## Child Property
The <xref:System.Windows.Forms.Integration.WindowsFormsHost> and <xref:System.Windows.Forms.Integration.ElementHost> classes can host only a single child control or element. To host more than one control or element, you must use a container as the child content. For example, you could add Windows Forms button and check box controls to a <xref:System.Windows.Forms.Panel?displayProperty=nameWithType> control, and then assign the panel to a <xref:System.Windows.Forms.Integration.WindowsFormsHost> control's <xref:System.Windows.Forms.Integration.WindowsFormsHost.Child%2A> property. However, you cannot add the button and check box controls separately to the same <xref:System.Windows.Forms.Integration.WindowsFormsHost> control.
<a name="scaling"></a>
## Scaling
[!INCLUDE[TLA2#tla_winclient](../../../includes/tla2sharptla-winclient-md.md)] and Windows Forms have different scaling models. Some [!INCLUDE[TLA2#tla_winclient](../../../includes/tla2sharptla-winclient-md.md)] scaling transformations are meaningful to Windows Forms controls, but others are not. For example, scaling a Windows Forms control to 0 will work, but if you try to scale the same control back to a non-zero value, the control's size remains 0. For more information, see [Layout Considerations for the WindowsFormsHost Element](layout-considerations-for-the-windowsformshost-element.md).
<a name="adapter"></a>
## Adapter
There may be confusion when working the <xref:System.Windows.Forms.Integration.WindowsFormsHost> and <xref:System.Windows.Forms.Integration.ElementHost> classes, because they include a hidden container. Both the <xref:System.Windows.Forms.Integration.WindowsFormsHost> and <xref:System.Windows.Forms.Integration.ElementHost> classes have a hidden container, called an *adapter*, which they use to host content. For the <xref:System.Windows.Forms.Integration.WindowsFormsHost> element, the adapter derives from the <xref:System.Windows.Forms.ContainerControl?displayProperty=nameWithType> class. For the <xref:System.Windows.Forms.Integration.ElementHost> control, the adapter derives from the <xref:System.Windows.Controls.DockPanel> element. When you see references to the adapter in other interoperation topics, this container is what is being discussed.
<a name="nesting"></a>
## Nesting
Nesting a <xref:System.Windows.Forms.Integration.WindowsFormsHost> element inside an <xref:System.Windows.Forms.Integration.ElementHost> control is not supported. Nesting an <xref:System.Windows.Forms.Integration.ElementHost> control inside a <xref:System.Windows.Forms.Integration.WindowsFormsHost> element is also not supported.
<a name="focus"></a>
## Focus
Focus works differently in [!INCLUDE[TLA2#tla_winclient](../../../includes/tla2sharptla-winclient-md.md)] and Windows Forms, which means that focus issues may occur in a hybrid application. For example, if you have focus inside a <xref:System.Windows.Forms.Integration.WindowsFormsHost> element, and you either minimize and restore the page or show a modal dialog box, focus inside the <xref:System.Windows.Forms.Integration.WindowsFormsHost> element may be lost. The <xref:System.Windows.Forms.Integration.WindowsFormsHost> element still has focus, but the control inside it may not.
Data validation is also affected by focus. Validation works in a <xref:System.Windows.Forms.Integration.WindowsFormsHost> element, but it does not work as you tab out of the <xref:System.Windows.Forms.Integration.WindowsFormsHost> element, or between two different <xref:System.Windows.Forms.Integration.WindowsFormsHost> elements.
<a name="property_mapping"></a>
## Property Mapping
Some property mappings require extensive interpretation to bridge dissimilar implementations between the [!INCLUDE[TLA2#tla_winclient](../../../includes/tla2sharptla-winclient-md.md)] and Windows Forms technologies. Property mappings enable your code to react to changes in fonts, colors, and other properties. In general, property mappings work by listening for either *Property*Changed events or On*Property*Changed calls, and setting appropriate properties on either the child control or its adapter. For more information, see [Windows Forms and WPF Property Mapping](windows-forms-and-wpf-property-mapping.md).
<a name="layoutrelated_properties_on_hosted_content"></a>
## Layout-related Properties on Hosted Content
When the <xref:System.Windows.Forms.Integration.WindowsFormsHost.Child%2A?displayProperty=nameWithType> or <xref:System.Windows.Forms.Integration.ElementHost.Child%2A?displayProperty=nameWithType> property is assigned, several layout-related properties on the hosted content are set automatically. Changing these content properties can cause unexpected layout behaviors.
Your hosted content is docked to fill the <xref:System.Windows.Forms.Integration.WindowsFormsHost> and <xref:System.Windows.Forms.Integration.ElementHost> parent. To enable this fill behavior, several properties are set when you set the child property. The following table lists which content properties are set by the <xref:System.Windows.Forms.Integration.ElementHost> and <xref:System.Windows.Forms.Integration.WindowsFormsHost> classes.
|Host Class|Content Properties|
|----------------|------------------------|
|<xref:System.Windows.Forms.Integration.ElementHost>|<xref:System.Windows.FrameworkElement.Height%2A><br /><br /> <xref:System.Windows.FrameworkElement.Width%2A><br /><br /> <xref:System.Windows.FrameworkElement.Margin%2A><br /><br /> <xref:System.Windows.FrameworkElement.VerticalAlignment%2A><br /><br /> <xref:System.Windows.FrameworkElement.HorizontalAlignment%2A>|
|<xref:System.Windows.Forms.Integration.WindowsFormsHost>|<xref:System.Windows.Forms.Control.Margin%2A><br /><br /> <xref:System.Windows.Forms.Control.Dock%2A><br /><br /> <xref:System.Windows.Forms.Control.AutoSize%2A><br /><br /> <xref:System.Windows.Forms.Control.Location%2A><br /><br /> <xref:System.Windows.Forms.Control.MaximumSize%2A>|
Do not set these properties directly on the hosted content. For more information, see [Layout Considerations for the WindowsFormsHost Element](layout-considerations-for-the-windowsformshost-element.md).
<a name="navigation_applications"></a>
## Navigation Applications
Navigation applications may not maintain user state. The <xref:System.Windows.Forms.Integration.WindowsFormsHost> element recreates its controls when it is used in a navigation application. Recreating child controls occurs when the user navigates away from the page hosting the <xref:System.Windows.Forms.Integration.WindowsFormsHost> element and then returns to it. Any content that has been typed in by the user will be lost.
<a name="message_loop_interoperation"></a>
## Message Loop Interoperation
When working with Windows Forms message loops, messages may not be processed as expected. The <xref:System.Windows.Forms.Integration.WindowsFormsHost.EnableWindowsFormsInterop%2A> method is called by the <xref:System.Windows.Forms.Integration.WindowsFormsHost> constructor. This method adds a message filter to the [!INCLUDE[TLA2#tla_winclient](../../../includes/tla2sharptla-winclient-md.md)] message loop. This filter calls the <xref:System.Windows.Forms.Control.PreProcessMessage%2A?displayProperty=nameWithType> method if a <xref:System.Windows.Forms.Control?displayProperty=nameWithType> was the target of the message and translates/dispatches the message.
If you show a <xref:System.Windows.Window> in a Windows Forms message loop with <xref:System.Windows.Forms.Application.Run%2A?displayProperty=nameWithType>, you cannot type anything unless you call the <xref:System.Windows.Forms.Integration.ElementHost.EnableModelessKeyboardInterop%2A> method. The <xref:System.Windows.Forms.Integration.ElementHost.EnableModelessKeyboardInterop%2A> method takes a <xref:System.Windows.Window> and adds a <xref:System.Windows.Forms.IMessageFilter?displayProperty=nameWithType>, which reroutes key-related messages to the [!INCLUDE[TLA2#tla_winclient](../../../includes/tla2sharptla-winclient-md.md)] message loop. For more information, see [Windows Forms and WPF Interoperability Input Architecture](windows-forms-and-wpf-interoperability-input-architecture.md).
<a name="opacity_and_layering"></a>
## Opacity and Layering
The <xref:System.Windows.Interop.HwndHost> class does not support layering. This means that setting the <xref:System.Windows.UIElement.Opacity%2A> property on the <xref:System.Windows.Forms.Integration.WindowsFormsHost> element has no effect, and no blending will occur with other [!INCLUDE[TLA2#tla_winclient](../../../includes/tla2sharptla-winclient-md.md)] windows which have <xref:System.Windows.Window.AllowsTransparency%2A> set to `true`.
<a name="dispose"></a>
## Dispose
Not disposing classes properly can leak resources. In your hybrid applications, make sure that the <xref:System.Windows.Forms.Integration.WindowsFormsHost> and <xref:System.Windows.Forms.Integration.ElementHost> classes are disposed, or you could leak resources. Windows Forms disposes <xref:System.Windows.Forms.Integration.ElementHost> controls when its non-modal <xref:System.Windows.Forms.Form> parent closes. [!INCLUDE[TLA2#tla_winclient](../../../includes/tla2sharptla-winclient-md.md)] disposes <xref:System.Windows.Forms.Integration.WindowsFormsHost> elements when your application shuts down. It is possible to show a <xref:System.Windows.Forms.Integration.WindowsFormsHost> element in a <xref:System.Windows.Window> in a Windows Forms message loop. In this case, your code may not receive notification that your application is shutting down.
<a name="enabling_visual_styles"></a>
## Enabling Visual Styles
Microsoft Windows XP visual styles on a Windows Forms control may not be enabled. The <xref:System.Windows.Forms.Application.EnableVisualStyles%2A?displayProperty=nameWithType> method is called in the template for a Windows Forms application. Although this method is not called by default, if you use Visual Studio to create a project, you will get Microsoft Windows XP visual styles for controls, if version 6.0 of Comctl32.dll is available. You must call the <xref:System.Windows.Forms.Application.EnableVisualStyles%2A> method before handles are created on the thread. For more information, see [How to: Enable Visual Styles in a Hybrid Application](how-to-enable-visual-styles-in-a-hybrid-application.md).
<a name="licensed_controls"></a>
## Licensed Controls
Licensed Windows Forms controls that display licensing information in a message box to the user might cause unexpected behavior for a hybrid application. Some licensed controls show a dialog box in response to handle creation. For example, a licensed control might inform the user that a license is required, or that the user has three remaining trial uses of the control.
The <xref:System.Windows.Forms.Integration.WindowsFormsHost> element derives from the <xref:System.Windows.Interop.HwndHost> class, and the child control’s handle is created inside the <xref:System.Windows.Forms.Integration.WindowsFormsHost.BuildWindowCore%2A> method. The <xref:System.Windows.Interop.HwndHost> class does not allow messages to be processed in the <xref:System.Windows.Forms.Integration.WindowsFormsHost.BuildWindowCore%2A> method, but displaying a dialog box causes messages to be sent. To enable this licensing scenario, call the <xref:System.Windows.Forms.Control.CreateControl%2A?displayProperty=nameWithType> method on the control before assigning it as the <xref:System.Windows.Forms.Integration.WindowsFormsHost> element's child.
<a name="wpf_designer"></a>
## WPF Designer
You can design your WPF content by using the WPF Designer for Visual Studio. The following sections list some common problems that can occur when authoring hybrid applications with the WPF Designer.
### BackColorTransparent is ignored at design time
The <xref:System.Windows.Forms.Integration.ElementHost.BackColorTransparent%2A> property might not work as expected at design time.
If a WPF control is not on a visible parent, the WPF runtime ignores the <xref:System.Windows.Forms.Integration.ElementHost.BackColorTransparent%2A> value. The reason that <xref:System.Windows.Forms.Integration.ElementHost.BackColorTransparent%2A> might be ignored is because <xref:System.Windows.Forms.Integration.ElementHost> object is created in a separate <xref:System.AppDomain>. However, when you run the application, <xref:System.Windows.Forms.Integration.ElementHost.BackColorTransparent%2A> does work as expected.
### Design-time Error List appears when the obj folder is deleted
If the obj folder is deleted, the Design-time Error List appears.
When you design using <xref:System.Windows.Forms.Integration.ElementHost>, the Windows Forms Designer uses generated files in the Debug or Release folder within your project's obj folder. If you delete these files, the Design-time Error List appears. To fix this problem, rebuild your project. For more information, see [Design-Time Errors in the Windows Forms Designer](/dotnet/framework/winforms/controls/design-time-errors-in-the-windows-forms-designer).
<a name="elementhost_and_ime"></a>
## ElementHost and IME
WPF controls hosted in an <xref:System.Windows.Forms.Integration.ElementHost> currently do not support the <xref:System.Windows.Forms.Control.ImeMode%2A> property. Changes to <xref:System.Windows.Forms.Control.ImeMode%2A> will be ignored by the hosted controls.
## See also
- <xref:System.Windows.Forms.Integration.ElementHost>
- <xref:System.Windows.Forms.Integration.WindowsFormsHost>
- [Interoperability in the WPF Designer](https://docs.microsoft.com/previous-versions/visualstudio/visual-studio-2010/bb628658(v=vs.100))
- [Windows Forms and WPF Interoperability Input Architecture](windows-forms-and-wpf-interoperability-input-architecture.md)
- [How to: Enable Visual Styles in a Hybrid Application](how-to-enable-visual-styles-in-a-hybrid-application.md)
- [Layout Considerations for the WindowsFormsHost Element](layout-considerations-for-the-windowsformshost-element.md)
- [Windows Forms and WPF Property Mapping](windows-forms-and-wpf-property-mapping.md)
- [Design-Time Errors in the Windows Forms Designer](/dotnet/framework/winforms/controls/design-time-errors-in-the-windows-forms-designer)
- [Migration and Interoperability](migration-and-interoperability.md)
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