GCHandle.Alloc Method (Object)
Allocates a Normal handle for the specified object.
Namespace: System.Runtime.InteropServices
Assembly: mscorlib (in mscorlib.dll)
Parameters
- value
- Type: System.Object
The object that uses the GCHandle.
Return Value
Type: System.Runtime.InteropServices.GCHandleA new GCHandle that protects the object from garbage collection. This GCHandle must be released with Free when it is no longer needed.
| Exception | Condition |
|---|---|
| ArgumentException | An instance with nonprimitive (non-blittable) members cannot be pinned. |
Normal handles are opaque, which means that you cannot resolve the address of the object it contains through the handle.
The following example shows an App class that creates a handle to a managed object using the GCHandle.Alloc method, which prevents the managed object from being collected. A call to the EnumWindows method passes a delegate and a managed object (both declared as managed types, but not shown), and casts the handle to an IntPtr. The unmanaged function passes the type back to the caller as a parameter of the callback function.
using System; using System.IO; using System.Threading; using System.Windows.Forms; using System.Runtime.InteropServices; using System.Security.Permissions; public delegate bool CallBack(int handle, IntPtr param); public class LibWrap { // passing managed object as LPARAM // BOOL EnumWindows(WNDENUMPROC lpEnumFunc, LPARAM lParam); [DllImport("user32.dll")] public static extern bool EnumWindows(CallBack cb, IntPtr param); } public class App { public static void Main() { Run(); } [SecurityPermission(SecurityAction.Demand, UnmanagedCode=true)] public static void Run() { TextWriter tw = System.Console.Out; GCHandle gch = GCHandle.Alloc(tw); CallBack cewp = new CallBack(CaptureEnumWindowsProc); // platform invoke will prevent delegate to be garbage collected // before call ends LibWrap.EnumWindows(cewp, GCHandle.ToIntPtr(gch)); gch.Free(); } private static bool CaptureEnumWindowsProc(int handle, IntPtr param) { GCHandle gch = GCHandle.FromIntPtr(param); TextWriter tw = (TextWriter)gch.Target; tw.WriteLine(handle); return true; } }
- SecurityCriticalAttribute
requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code.
Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
