What causes "Operation cannot be performed." in dotnet/wpf?

Pass a valid dotted-quad IPv4 string (e.g. "192.168.0.1") with exactly 4 octets in 0-255

dotnet/wpf · error · InvalidOperationException

Operation cannot be performed.

Error message

Operation cannot be performed.

What it means

IValueProvider.SetValue parses the string with GetIPAddressFromString; if the string is not a valid IPv4 address, the proxy throws InvalidOperationException('Operation cannot be performed') instead of sending IPM_SETADDRESS. Only valid 4-octet IPv4 values are accepted.

Solutions

Pass a valid dotted-quad IPv4 string (e.g. "192.168.0.1") with exactly 4 octets in 0-255
Pre-validate the string with IPAddress.TryParse before calling SetValue
Catch InvalidOperationException and report the invalid input to the caller
Trim/handle whitespace and ensure the test data has no typos

Example fix

// before
valuePattern.SetValue(userInput);
// after
if (System.Net.IPAddress.TryParse(userInput, out var ip) && ip.AddressFamily == AddressFamily.InterNetwork && userInput.Split('.').Length == 4)
{
    valuePattern.SetValue(userInput);
}
else
{
    throw new FormatException($"'{userInput}' is not a valid IPv4 address.");
}

Defensive patterns

Strategy: validation

Validate before calling

bool valid = System.Net.IPAddress.TryParse(val, out var ip) && val.Split('.').Length == 4 && ip.AddressFamily == AddressFamily.InterNetwork;

Try / catch

try { valuePattern.SetValue(val); }
catch (InvalidOperationException) { /* invalid IPv4 string; report or fix input */ }

Prevention

Pre-validate with IPAddress.TryParse and require 4 octets
Reject IPv6 for SysIPAddress32 controls
Trim whitespace from user/config input
Use canonical dotted-quad strings in test data

When it happens

Trigger: Calling IValueProvider.SetValue with strings like "abc", "999.1.1.1", "1.2.3" (3 octets), or empty string; GetIPAddressFromString returns null so control reaches the throw at the end of SetValue.

Common situations: Passing IPv6 addresses to an IPv4-only SysIPAddress32 control; whitespace/typos in test data; localized or malformed input from a config file.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/d25473018f02c282. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/UIAutomation/UIAutomationClientSideProviders/MS/Internal/AutomationProxies/WindowsIPAddress.cs:143

                byte[] abOctet = ipAddress.GetAddressBytes();

                if (abOctet.Length == 4)
                {
                    uint ipV4 = 0;

                    for (int iPos = 0; iPos < 4; iPos++)
                    {
                        ipV4 = (ipV4 << 8) + abOctet[iPos];
                    }

                    // no return result for this message, so if it get sent it must have succeeded
                    Misc.ProxySendMessage(_hwnd, NativeMethods.IPM_SETADDRESS, IntPtr.Zero, (IntPtr)unchecked((int)ipV4));
                    return;
                }
            }

            // this was no a valid IP address
            throw new InvalidOperationException (SR.OperationCannotBePerformed);
        }


        // Request to get the value that this UI element is representing as a string
        string IValueProvider.Value
        {
            get
            {
                return Misc.ProxyGetText(_hwnd, IP_ADDRESS_STRING_LENGTH);
            }
        }

        bool IValueProvider.IsReadOnly
        {
            get
            {
                return !Misc.IsEnabled(_hwnd);
            }

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