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[.NET/CoreFoundation] Use [UnmanagedCallersOnly] instead of [MonoPInvokeCallback] for the CGPDFDictionaryApplyFunction function. #12956

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Oct 8, 2021
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[.NET/CoreFoundation] Use [UnmanagedCallersOnly] instead of [MonoPInvokeCallback] for the CGPDFDictionaryApplyFunction function. #12956

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36 changes: 31 additions & 5 deletions src/CoreGraphics/CGPDFDictionary.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -154,51 +154,77 @@ public bool GetArray (string key, out CGPDFArray array)
return r;
}

#if NET
[DllImport (Constants.CoreGraphicsLibrary)]
unsafe extern static void CGPDFDictionaryApplyFunction (/* CGPDFDictionaryRef */ IntPtr dic, delegate* unmanaged<IntPtr, IntPtr, IntPtr, void> function, /* void* */ IntPtr info);
#else
// CGPDFDictionaryApplierFunction
delegate void ApplierFunction (/* const char* */ string key, /* CGPDFObjectRef */ IntPtr value, /* void* */ IntPtr info);
delegate void ApplierFunction (/* const char* */ IntPtr key, /* CGPDFObjectRef */ IntPtr value, /* void* */ IntPtr info);
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Could this be left as string and add in a [MarhsalAs(UnmanagedType. LPUTF8Str)] to the string parameter?

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No, because parameters and the return type for methods decorated with [UnmanagedCallersOnly] must be blittable, and string isn't blittable (and the MarshalAs attribute doesn't change that fact).

Now technically this delegate could be left with the string argument, because it's only used in legacy Xamarin (and not where we apply the [UnmanagedCallersOnly] attribute), but that would mean we'd have different implementations of the ApplyBridge function between the legacy and .NET - one with a string argument and one with an IntPtr argument. I opted for changing the parameter type in legacy Xamarin to be able to share more code with .NET.

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👍


[DllImport (Constants.CoreGraphicsLibrary)]
extern static void CGPDFDictionaryApplyFunction (/* CGPDFDictionaryRef */ IntPtr dic, ApplierFunction function, /* void* */ IntPtr info);

static readonly ApplierFunction applyblock_handler = ApplyBridge;
#endif // NET

public delegate void ApplyCallback (string key, object value, object info);

#if NET
[UnmanagedCallersOnly]
#else
#if !MONOMAC
[MonoPInvokeCallback (typeof (ApplierFunction))]
#endif
static void ApplyBridge (string key, IntPtr pdfObject, IntPtr info)
#endif // NET
static void ApplyBridge (IntPtr key, IntPtr pdfObject, IntPtr info)
{
var data = (Tuple<ApplyCallback, object>) GCHandle.FromIntPtr (info).Target;
var callback = data.Item1;

callback (key, CGPDFObject.FromHandle (pdfObject), data.Item2);
callback (Marshal.PtrToStringUTF8 (key), CGPDFObject.FromHandle (pdfObject), data.Item2);
}

public void Apply (ApplyCallback callback, object info = null)
{
var data = new Tuple<ApplyCallback, object> (callback, info);
var gch = GCHandle.Alloc (data);
try {
#if NET
unsafe {
CGPDFDictionaryApplyFunction (Handle, &ApplyBridge, GCHandle.ToIntPtr (gch));
}
#else
CGPDFDictionaryApplyFunction (Handle, applyblock_handler, GCHandle.ToIntPtr (gch));
#endif
} finally {
gch.Free ();
}
}

#if NET
[UnmanagedCallersOnly]
#else
#if !MONOMAC
[MonoPInvokeCallback (typeof (ApplierFunction))]
#endif
static void ApplyBridge2 (string key, IntPtr pdfObject, IntPtr info)
#endif // NET
static void ApplyBridge2 (IntPtr key, IntPtr pdfObject, IntPtr info)
{
var callback = (Action<string,CGPDFObject>) GCHandle.FromIntPtr (info).Target;

callback (key, new CGPDFObject (pdfObject));
callback (Marshal.PtrToStringUTF8 (key), new CGPDFObject (pdfObject));
}

public void Apply (Action<string,CGPDFObject> callback)
{
GCHandle gch = GCHandle.Alloc (callback);
#if NET
unsafe {
CGPDFDictionaryApplyFunction (Handle, &ApplyBridge2, GCHandle.ToIntPtr (gch));
}
#else
CGPDFDictionaryApplyFunction (Handle, ApplyBridge2, GCHandle.ToIntPtr (gch));
#endif
gch.Free ();
}

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