WPF设计器实例化对象并导致编译器错误

Question

I have solution called MySol .

I have a DLL project in MySol called DeviceProj . This project defines a class:

public class Device
{
    public int NumFields { get; set; }
}

I also have a WPF UserControl project in MySol called DeviceControl . This class looks something like this:

public class DeviceControl : UserControl
{
    private Device _MyDevice;

    public Device MyDevice 
    {
        get { return _MyDevice; }
        set
        {
            _MyDevice = value;
            for (var i = 0; i < _MyDevice.NumFields; i++)
                Main.Children.Add(new TextBox());
        }
    }

    public DeviceControl()
    {
        MyDevice = new Device { NumFields = 4 };

        InitializeComponent();
    }
}

Finally, I have a WPF Application project in MySol called DeviceWindow . When I add a DeviceControl to the DeviceWindow Designer, I see my control with 4 text boxes (this is expected: the designer creates an instance of DeviceControl and, since the default Device has its NumFields property set to 4, there are 4 text boxes).

But, when I compile MySol , I get the error:

Error 1 Unable to copy file "C:\\path\\to\\Device.dll" to "bin\\Debug\\Device.dll". The process cannot access the file 'bin\\Debug\\Device.dll' because it is being used by another process.

I assume this is because an instance of Device is being used by the WPF designer, so the DLL cannot be overwritten.

Is there any way around this problem?

Shorter, easier to understand (maybe?) explanation:

The WPF Window designer creates an instance of all UserControls declared in the window. If one of those UserControls contains a reference to an object declared in a different project (we'll call it ObjectProject ) in the same solution, the solution will not build because the ObjectProject .dll will be in use by the WPF designer. Visual Studio cannot overwrite .dll files that are in use.

Answer 1

The cause of this issue is your .DLL and your WPF application targets may differ. Your application target may be Client Profile. Keep both the target to same.

For example, if your library targets .NET 4, make sure your WPF Application targets also 4, not client profile.

Answer 2

Go to C:\\path\\to\\Device.dll and bin\\Debug\\Device.dll folder of your project then delete the Device.dll file from these two locations. When you run your project again, these files will be created automatically in the directory. Then you can build without this error.