Type.GetType() returning null

Question

I have a web application that dynamically creates a web page using usercontrols.

Within my code I have the following:

    private void Render_Modules()
    {
        foreach (OnlineSystemPageCustom.OnlineSystemPageHdr.OnlineSystemPageModule item in custompage.Header.Modules)
        {
            if (item.ModuleCustomOrder != 99 && !item.ModuleOptional)
            {
                string typeName = item.ModuleInternetFile;
                Type child = Type.GetType(typeName);
                webonlinecustombase ctl = (webonlinecustombase)Page.LoadControl("../IPAM_Controls/webtemplatecontrols/" + child.Name.ToString() + ".ascx");
                ctl.Event = Event;
                ctl.custompage = custompage;
                ctl.custommodule = item;
                this.eventprogrammodules.Controls.Add(ctl);
            }
        }
    }

The "typeName" that is being returned (example) is:

IPAMIntranet.IPAM_Controls.webtemplatecontrols.eventorgcommittee

The namespace for the user controls is as follows:

namespace IPAMIntranet.IPAM_Controls

The problem I am having is that Type.GetType(typeName) is returning null. What am I missing here?

Solution 1

Type.GetType(string) only looks in the currently executing assembly and mscorlib when you don't specify the assembly name within the string.

Options:

• Use the assembly-qualified name instead
• Call Assembly.GetType(name) on the appropriate assembly instead

If you have an easy way of getting hold of the relevant assembly (e.g. via typeof(SomeKnownType).Assembly) then the second option is probably simpler.

Solution 2

Type.GetType looks as the calling assembly, and a few system assemblies. For anything else, you must either use assemblyInstance.GetType(typeName), or you must use the "assembly qualified name" of the type, which includes the assembly details in which the type can be found. Otherwise, it wont be found, and will return null. You can get that from:

string aqn = someType.AssemblyQualifiedName;

Comments

[mattgcon]

assembly-qualified name? where do I get that? These are custom user controls that I created within the web application itself if that helps

[mattgcon]

how do I get the assembly qualified name for the user controls

[Marc Gravell]

@mattgcon I included that in the answerr

[Jon Skeet]

@mattgcon: You can use Type.AssemblyQualifiedName, but if you know it's for a specific assembly, you could use typeof(SomeClassInTheAssembly).Assembly to get that assembly, then use Assembly.GetType(string). It doesn't matter which class you use from the assembly to get a reference to it.

[mattgcon]

After I get the assembly then what do I do? Do I state Type child = Assembly.GetType(typeName) to get the user control?

[mattgcon]

if the someType is my typeName, I have to say that typeName is going to be dynamic and I have no idea what it is during design time.

[Jon Skeet]

@mattgcon: Yes, exactly... except using the assembly reference instead of just Assembly.

[mattgcon]

ok so I added the following: 'Assembly aqn = typeof(webonlinecustombase).Assembly' then 'Type child = aqn.GetType(typeName)' but it is still returning null

[Jon Skeet]

@mattgcon: Then it sounds like either your type name is wrong, or that type isn't in the same assembly as webonlinecustombase. (Is that really the name of a type? You might want to look at the .NET naming conventions.)

[mattgcon]

let us continue this discussion in chat

[Jon Skeet]

@mattgcon: Sorry, chat doesn't really work for my lifestyle. Let's stick to comments.

[Marc Gravell]

@matt somewhere, somehow, you have some strings. What I am saying is: store them as the assembly-qualified version. Or: if they all come from the same dll, use Assembly.GetType

[mattgcon]

Ok not a problem. the type is being returned from a SQL database with a type such as: 'IPAMIntranet.IPAM_Controls.webtemplatecontrols.eventorgcomm‌​ittee' the usercontrol that I created has a filename of eventorgcommittee.ascx. Both eventorgcommittee.ascx and webonlinecustombase.ascx are located within the same folder

[mattgcon]

The thing is these are not precompiled usercontrols that I added with a dll. they are actual usercontrol files within the web application. They are located in a sub folder within the web application.

[Jon Skeet]

@mattgcon: I don't know the details of on-the-fly compilation in ASP.NET - I suggest you try to open one of the generated assemblies in Reflector, and see what's in it. Alternatively, try to change your design so that you don't need quite this approach...

[mattgcon]

what I dont understand is, why do I need to call a different assembly if the user control files are not pre compiled from a dll and instead located as files within my web application.

[Marc Gravell]

@web just create one, and see what the assembly-qualified-name is. IIRC they follow a pattern.

[Jon Skeet]

@mattgcon: Well the types are being created on-the-fly... I'd hoped it would be compiling all of the user controls in one assembly, which would make it work... but if it only compiles them on a "just in time" basis, you'll end up with one assembly per control, which makes it all harder.

[mattgcon]

You are correct in the fact that it is one assembly per control. Here is a question, how would I take that string for the type and do a typeof(class) on it?

[Jon Skeet]

@mattgcon: You can't, because the type reference basically isn't known at compile-time - because it's compiled at execution time.

[mattgcon]

hmmm well that makes things more difficult then. and it has to be done this way.

[Jon Skeet]

@mattgcon: It's not clear exactly what you mean by that. Do you have to use non-precompiled user-controls? (If you precompiled them, they could all be in the same assembly.) Does the logic have to be in those user controls? You could have a class which basically used typeof for each user control you cared about, creating a mapping from string to type - but that would basically force the early compilation anyway.

[mattgcon]

oh what I meant was that the loading of the controls has to be at runtime. The webonlinecustombase is the base usercontrol for all of the dynamically loaded controls if that helps

[mattgcon]

I might have just solved my issue hold on and I will return with my results

[mattgcon]

Ok this was solved by simply putting stripping off everything except for the control name from typePath and placing it in the LoadControl statement.

[Jon Skeet]

@mattgcon: Ah, excellent - glad you sorted it in the end!

[AKS]

@skeet , using Assemly... gives error that "An object reference is required for the non-static field, method, or property 'System.Reflection.Assembly.GetType(string)'

[Jon Skeet]

@AKS: Hence the "on the appropriate assembly" part. You need to have a reference to the relevant Assembly first...