[MonoTouch] linking dependency

[Jeff Stedfast]

Hi Josh,

If you are writing a binding to a native library, you probably want to take
advantage of LinkWithAttribute(s) instead of specifying gcc flags in
MonoDevelop.

The LinkWithAttribute is an assembly level attribute that you probably want
to either put in your AssemblyInfo.cs, or, if you are using monoDevelop's
"MonoTouch Binding Library" project template, in the code-behind file named
<libMyLibrary>.linkwith.cs that gets auto-generated when you add
libMyLibrary.a to your project[1].

This attribute will look something like this:

[assembly: LinkWith ("libMyLibrary.a", LinkTarget.Simulator |
LinkTarget.ArmV6 | LinkTarget.ArmV7, ForceLoad = true)]

(MonoDevelop smartly auto-detects which architectures the .a is compatible
with, so it's probably safe to leave that field alone)

There are a few other properties for LinkWithAttributes that you can set:

* LinkerFlags: This is where you can list other linker flags you'd like to
pass, e.g. in your cause you'd set it to: "-lz -lsqlite3"

* Frameworks: This allows you to specify a list of frameworks that the
native library depends on, e.g.: "Foundation UIKit"

(in your case, you can leave it empty because both Foundation and UIKit
will be pulled in by the main application anyway, but it doesn't hurt to
add them)

* WeakFrameworks: Same idea as Frameworks, but for weak framework
references.

* IsCxx: This is a boolean property that specifies whether or not the
native library requires the use of the c++ linker. Defaults to false.

* NeedsGccExceptionHandling: Another boolean property which is sometimes
needed by c++ libraries (set to true if the native library requires linking
with -lgcc_eh).

* ForceLoad: This is a boolean hint for the compiler to use -force_load on
the native library (this usually needs to be set to true).


So, for your particular example, you'd probably want a LinkWith similar to
the following:

[assembly: LinkWith ("libMyLibrary.a", LinkTarget.Simulator |
LinkTarget.ArmV6 | LinkTarget.ArmV7, LinkerFlags = "-lz -lsqlite3",
ForceLoad = true)]


Hope that helps answer your question,

Jeff


1. Note: There's a bug in MonoDevelop 2.8.6.* that will cause MonoDevelop
to re-generate the *.linkwith.cs files every time you open the project
(sorry about that, it's my fault). Hopefully 2.8.8 stable will be going out
later this week or next week.


On Tue, Mar 13, 2012 at 1:32 PM, Josh Handel <jhandel at gmail.com> wrote:

> Howdy all,
>   I am trying to wrap Localystics API and its dependent on a few
> libraries (like sqlite).. I have read thru the binding documentation
> but I am still confused where in MonoDevelop to put my extra GCC flags
> to link libraries.. I need to link the following libraries (I think,
> maybe more).
>
> * libz.dylib
> * UIKit.framework
> * libsqlite3.dylib
>
> It also uses Foundation.framework but I don't think thats an issue :-P
>
> Thanks
> Josh Handel
> PS: Thanks for making a Binding Library project.. Last time I did
> binding I had to do it all from commandline (ick).
> _______________________________________________
> MonoTouch mailing list
> MonoTouch at lists.ximian.com
> http://lists.ximian.com/mailman/listinfo/monotouch
>
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