CODEWITHSUNDEEP
c#reflectionout-parameters
ldp615
ldp615

Reputation: 952

How can I invoke a method with an out parameter?

I want expose WebClient.DownloadDataInternal method like below:

[ComVisible(true)]
public class MyWebClient : WebClient
{
    private MethodInfo _DownloadDataInternal;

    public MyWebClient()
    {
        _DownloadDataInternal = typeof(WebClient).GetMethod("DownloadDataInternal", BindingFlags.NonPublic | BindingFlags.Instance);
    }

    public byte[] DownloadDataInternal(Uri address, out WebRequest request)
    {
        _DownloadDataInternal.Invoke(this, new object[] { address, out request });
    }

}

WebClient.DownloadDataInternal has a out parameter, I don't know how to invoke it. Help!

Upvotes: 50

Views: 31673

Answers (2)

dtb
dtb

Reputation: 217293

public class MyWebClient : WebClient
{
    delegate byte[] DownloadDataInternal(Uri address, out WebRequest request);

    DownloadDataInternal downloadDataInternal;

    public MyWebClient()
    {
        downloadDataInternal = (DownloadDataInternal)Delegate.CreateDelegate(
            typeof(DownloadDataInternal),
            this,
            typeof(WebClient).GetMethod(
                "DownloadDataInternal",
                BindingFlags.NonPublic | BindingFlags.Instance));
    }

    public byte[] DownloadDataInternal(Uri address, out WebRequest request)
    {
        return downloadDataInternal(address, out request);
    }
}

Upvotes: 25

JaredPar
JaredPar

Reputation: 754715

You invoke a method with an out parameter via reflection just like any other method. The difference is that the returned value will be copied back into the parameter array so you can access it from the calling function. 

object[] args = new object[] { address, request };
_DownloadDataInternal.Invoke(this, args);
request = (WebRequest)args[1];

Upvotes: 129

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