Trying to open another's application configuration file

Question

I'm developing a WinForm application with C# and .NET Framework 4.7.

With this application I'm trying to load the configuration file from another application:

string applicationName = Environment.GetCommandLineArgs()[1];

if (!string.IsNullOrWhiteSpace(applicationName))
{
    if (!applicationName.EndsWith(".exe"))
        applicationName += ".exe";

    string exePath = 
        Path.Combine(Environment.CurrentDirectory, applicationName);

    try
    {
        // Get the configuration file. The file name has
        // this format appname.exe.config.
        System.Configuration.Configuration config =
          ConfigurationManager.OpenExeConfiguration(exePath);

But ConfigurationManager.OpenExeConfiguration(exePath) throw an exception:

An error occurred while loading the configuration file: The 'exePath' parameter is not valid.
Parameter name: exePath

The configuration file, AnotherApp.exe.config, exists in the folder Environment.CurrentDirectory. I have also tried changing it to Path.Combine(@"D:\", applicationName); and I get the same exception.

If I add the exe.config, instead of .exe, at the end of the name here, applicationName += ".exe";, it seems to open something: config.FilePath is D:\AnotherApp.exe.config.config. But config object is empty. It hasn't filled any property.

What am I doing wrong?

I have copied the code from Microsoft documentation.

Answer 1

Before attempting to open AnotherApp.exe.config, ConfigurationManager.OpenExeConfiguration checks to see whether AnotherApp.exe exists on disk. Here's the source:

// ...
else {
    applicationUri = Path.GetFullPath(exePath);
    if (!FileUtil.FileExists(applicationUri, false))
        throw ExceptionUtil.ParameterInvalid("exePath");

    applicationFilename = applicationUri;
}

// Fallback if we haven't set the app config file path yet.
if (_applicationConfigUri == null) {
    _applicationConfigUri = applicationUri + ConfigExtension;
}

As you can see, the exePath is ultimately passed into FileUtils.FileExists, which ends up checking whether exePath represents a file on disk. In your case, this is AnotherApp.exe, which does not exist. The throw ExceptionUtil.ParameterInvalid("exePath"); statement is where your error is coming from.

Further down in the source I've included above, you can see _applicationConfigUri is set to AnotherApp.exe.config (it's an absolute path, but I've used a relative path for simplicity). When you set your exePath to AnotherApp.exe.config, the code ends up checking for the existence of AnotherApp.exe.config (it thinks this is the exe itself), which it finds. After this, _applicationConfigUri is set to AnotherApp.exe.config.config which does not exist, but the configuration system does not error out in this scenario (instead returning an empty configuration object).

It appears there may be two options for solving this:

1. Include AnotherApp.exe alongside AnotherApp.exe.config.
2. Use ConfigurationManager.OpenMappedExeConfiguration, which allows you to provide your own ExeConfigurationFileMap for instructing the configuration system on how to locate the .config file. If you need help with this, let me know and I'll include an example of how this should work.