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PODelphi interface from DLL
 

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  1. PODelphi interface from DLL
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    <p>Using Delphi XE.</p> <p>When trying to access a Delphi interface object from a DLL, it fails if I try to do it dynamically versus statically.</p> <p>The interface unit in the dll implements a function to return an instance of the interface. When linked statically, the result is nil when entering the function and everything works. When loading dynamically, the result is non-nil, so when the assignment to result is being done, the IntFCopy code sees it as non-nil and so tries to free it before the assignment, which raises an exception.</p> <p>Any insight would be appreciated.</p> <p>The DLL includes testinterfaceload_u and exports testInt:</p> <pre><code>library testinterfaceload; uses SimpleShareMem, SysUtils, Classes, testinterfaceload_u in 'testinterfaceload_u.pas'; {$R *.res} exports testInt; begin end. </code></pre> <p>testinterfaceload_u is the unit that defines the interface and simple class implementation:</p> <pre><code>unit testinterfaceload_u; interface type ITestInt = interface procedure Test; end; {this function returns an instance of the interface} function testInt : ITestInt; stdcall; export; type TTestInt = class(TInterfacedObject,ITestInt) procedure Test; end; implementation function testInt : ITestInt; begin //debugger shows result as non-nil ITestInt even before this assignment, when dynamic result := TTestInt.Create; end; procedure TTestInt.Test; var i : integer; begin i := 0; end; end. </code></pre> <p>Here's a console app that loads the dll and calls the testInt function to return the interface:</p> <pre><code>program testload_console; {$APPTYPE CONSOLE} uses SysUtils, Windows, testinterfaceload_u in 'testinterfaceload_u.pas'; type TTestInt = function() : ITestInt; var TestInt: TTestInt; NewTestInt : ITestInt; DLLHandle: THandle; begin DLLHandle := LoadLibrary('testinterfaceload.dll'); if (DLLHandle &lt; HINSTANCE_ERROR) then raise Exception.Create('testinterfaceload.dll can not be loaded or not found. ' + SysErrorMessage(GetLastError)); @TestInt := GetProcAddress(DLLHandle, 'testInt'); try if Assigned(TestInt) then NewTestInt := TestInt; except on e:Exception do WriteLn(Output,e.Message); end; end. </code></pre>
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    1. COWhy use explicit LoadLibrary rather than implicit linking?
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      1. USDavid Heffernan
    2. COI'm having a problem in InstallAware trying to run one of my dll's that calls another of my dll's. InstallAware seems to choke when trying to unload the libraries if the second dll is loaded, so I was trying to handle its lifespan in the first dll.
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    3. CO`if (DLLHandle < HINSTANCE_ERROR) then` is incorrect. `LoadLibrary` returns 0 (i.e. `NULL`) in case of error. Also, `export` is not needed and just serves to confuse. Remove it.
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