Load contexts and Type.GetType
Type.GetType(AN,T) actually translates to Assembly.Load(AN).GetType(T). This actually can be the cause of many confusions. Often programmers end up in a situation where they have explicitly loaded the assembly, but Type.GetType is not able to find the type from the assembly they just loaded.
Let us look into the sample below. Let us do a Type.GetType for Foo and provide the path to the location of Foo in the config file as mentioned below.
Copy the source below to TypeSample.cs and the config to TypeSample.exe.config
using System;
using System.Reflection;
class DomSample {
public static void Main(){
try {
Type ty1 = Type.GetType("Foo, Foo, Version=1.0.0.0, Culture=neutral, PublicKeyToken=1faea1974f697f94");
if (ty1 != null) {
Console.WriteLine("V1 Type = {0}", ty1.Assembly.FullName.ToString());
}
else {
Console.WriteLine("Unable to find type ...");
}
}
catch (Exception e) {
Console.WriteLine(e.ToString());
}
}
}
<configuration>
<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<probing privatePath="v1" />
</assemblyBinding>
</runtime>
</configuration>
Make sure that you create a path v1 under APPBASE and create a Foo.cs which is compiled and signed to Foo.dll. Copy the following source to Foo.cs and comple it to Foo.dll and sign it with the key (see my article on signinig)
using System;
using System.Reflection;
[assembly: System.Reflection.AssemblyVersion("1.0.0.0")]
public class Foo {
public void Bar() {
Console.WriteLine("Version = {0}", (Assembly.GetExecutingAssembly()).ToString());
}
}
If you run TypeSample.exe you will get the following output
V1 Type = Foo, Version=1.0.0.0, Culture=neutral, PublicKeyToken=1faea1974f697f94
If you run the sample under ntsd you will notice that Foo.dll is loaded from directory v1 in the default AppDomain
Opened log file 'ntsd.log'
0:000> !dumpdomain
--------------------------------------
System Domain: 7a390b60
LowFrequencyHeap: 7a390b84
HighFrequencyHeap: 7a390be0
StubHeap: 7a390c3c
Stage: OPEN
Name: None
--------------------------------------
Shared Domain: 7a391138
LowFrequencyHeap: 7a39115c
HighFrequencyHeap: 7a3911b8
StubHeap: 7a391214
Stage: OPEN
Name: None
Assembly: 001e8828
--------------------------------------
Domain 1: 001b0890
LowFrequencyHeap: 001b08b4
HighFrequencyHeap: 001b0910
StubHeap: 001b096c
Stage: OPEN
SecurityDescriptor: 001b1a98
Name: DomSample.exe
Assembly: 001e8828 [C:\Windows\assembly\GAC_32\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll]
ClassLoader: 001e88c0
SecurityDescriptor: 001e8738
Module Name
790c2000 C:\Windows\assembly\GAC_32\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll
Assembly: 001f95e0 [c:\blog\May2007\DomSample.exe]
ClassLoader: 001f9678
SecurityDescriptor: 001f94e0
Module Name
00712c24 c:\blog\May2007\DomSample.exe
Assembly: 00208128 [c:\blog\May2007\v1\Foo.dll]
ClassLoader: 00208398
SecurityDescriptor: 00208298
Module Name
007130d8 c:\blog\May2007\v1\Foo.dll
Now let us modify the code above to use LoadFrom and then try the Type.GetType.
Copy the code below to TypeSampleLoadFrom.cs and compile it to TypeSampleLoadFrom.exe. Let us not provide a config file this time such Type.GetType cannot find the assembly Foo when it tries to load it.
using System;
using System.Reflection;
class DomSample {
public static void Main() {
try {
Assembly.LoadFrom("c:\\Blog\\May2007\\v2\\Foo.dll");
Type ty1 = Type.GetType("Foo, Foo, Version=1.0.0.0, Culture=neutral, PublicKeyToken=1faea1974f697f94");
if(ty1 != null) {
Console.WriteLine("V1 Type = {0}",ty1.Assembly.FullName.ToString());
}
else {
Console.WriteLine("Unable to find type ...");
}
}
catch(Exception e) {
Console.WriteLine(e.ToString());
}
}
}
The above program yields the result "Unable to find type ...". If you watch the program under ntsd you will notice that Foo.dll is loaded from the LoadFrom, but the Type.GetType was not able to use the already loaded Foo.dll or find Foo.dll to load it to retreive the type information
0:001> !dumpdomain
--------------------------------------
System Domain: 7a390b60
LowFrequencyHeap: 7a390b84
HighFrequencyHeap: 7a390be0
StubHeap: 7a390c3c
Stage: OPEN
Name: None
--------------------------------------
Shared Domain: 7a391138
LowFrequencyHeap: 7a39115c
HighFrequencyHeap: 7a3911b8
StubHeap: 7a391214
Stage: OPEN
Name: None
Assembly: 002e86e8
--------------------------------------
Domain 1: 002b08c8
LowFrequencyHeap: 002b08ec
HighFrequencyHeap: 002b0948
StubHeap: 002b09a4
Stage: OPEN
Name: DomSample1.exe
Assembly: 002e86e8 [C:\Windows\assembly\GAC_32\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll]
ClassLoader: 002e8780
SecurityDescriptor: 002f4ef8
Module Name
790c2000 C:\Windows\assembly\GAC_32\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll
Assembly: 002fa790 [c:\blog\May2007\DomSample1.exe]
ClassLoader: 002fa828
SecurityDescriptor: 002fa690
Module Name
00102c24 c:\blog\May2007\DomSample1.exe
Assembly: 00302bc0 [c:\Blog\May2007\v2\Foo.dll]
ClassLoader: 003072b0
SecurityDescriptor: 00306b88
Module Name
00103120 c:\Blog\May2007\v2\Foo.dll
Let us modify the above sample and add a config TypeSampleLoadFrom.exe.config as follows
<configuration>
<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<probing privatePath="v1" />
</assemblyBinding>
</runtime>
</configuration>
You will get the output V1 Type = Foo, Version=1.0.0.0, Culture=neutral, PublicKeyToken=1faea1974f697f94.
If you run the program under the debugger you will find that there are two Foo.dll loaded in the default AppDomain one loaded from the LoadFrom context and the other load by Type.GetType in the other context. I had specifically placed the same Foo.dll in different locations to make this happen. The Foo.dll loaded by Type.GetType was loaded from v1 directory and the Foo.dll loaded from the LoadFrom context was loaded from v2 directory. If you had both point to the same location, you will however see only one copy of the dll.
0:000> !dumpdomain
--------------------------------------
System Domain: 7a390b60
LowFrequencyHeap: 7a390b84
HighFrequencyHeap: 7a390be0
StubHeap: 7a390c3c
Stage: OPEN
Name: None
--------------------------------------
Shared Domain: 7a391138
LowFrequencyHeap: 7a39115c
HighFrequencyHeap: 7a3911b8
StubHeap: 7a391214
Stage: OPEN
Name: None
Assembly: 003386f8
--------------------------------------
Domain 1: 003008a0
LowFrequencyHeap: 003008c4
HighFrequencyHeap: 00300920
StubHeap: 0030097c
Stage: OPEN
SecurityDescriptor: 00301aa8
Name: DomSample1.exe
Assembly: 003386f8 [C:\Windows\assembly\GAC_32\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll]
ClassLoader: 00338790
SecurityDescriptor: 00344ed0
Module Name
790c2000 C:\Windows\assembly\GAC_32\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll
Assembly: 0034a7c8 [c:\blog\May2007\DomSample1.exe]
ClassLoader: 0034a860
SecurityDescriptor: 0034a6c8
Module Name
002d2c24 c:\blog\May2007\DomSample1.exe
Assembly: 00365b00 [c:\Blog\May2007\v2\Foo.dll]
ClassLoader: 00365998
SecurityDescriptor: 00358038
Module Name
002d3120 c:\Blog\May2007\v2\Foo.dll
Assembly: 00366bd0 [c:\blog\May2007\v1\Foo.dll]
ClassLoader: 00366a58
SecurityDescriptor: 00365c48
Module Name
002d3548 c:\blog\May2007\v1\Foo.dll