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| 1 | <!doctype HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" > | ||
| 2 | <html> | ||
| 3 | <head> | ||
| 4 | <title>Proxy Class for Managed Custom Actions</title> | ||
| 5 | <meta http-equiv="Content-Type" content="text/html; charset=Windows-1252"> | ||
| 6 | <link rel="stylesheet" type="text/css" href="MSDN.css"> | ||
| 7 | </head> | ||
| 8 | <body id="bodyID" class="dtBODY"> | ||
| 9 | <div id="nsbanner"> | ||
| 10 | <div id="bannerrow1"> | ||
| 11 | <table class="bannerparthead" cellspacing="0" id="Table1"> | ||
| 12 | <tr id="hdr"> | ||
| 13 | <td class="runninghead">Managed Libraries for Windows Installer</td> | ||
| 14 | <td class="product"></td> | ||
| 15 | </tr> | ||
| 16 | </table> | ||
| 17 | </div> | ||
| 18 | <div id="TitleRow"> | ||
| 19 | <h1 class="dtH1">Proxy for Managed Custom Actions</h1> | ||
| 20 | </div> | ||
| 21 | </div> | ||
| 22 | <div id="nstext"> | ||
| 23 | <p>The custom action proxy allows an MSI developer to write | ||
| 24 | custom actions in managed code, while maintaing all the advantages of type 1 | ||
| 25 | DLL custom actions including full access to installer state, properties, | ||
| 26 | and the session database.</p> | ||
| 27 | <p>There are generally four problems that needed to be | ||
| 28 | solved in order to create a type 1 custom action in managed code:</p> | ||
| 29 | <ol> | ||
| 30 | <li><p><strong>Exporting the CA function as a native entry point callable by | ||
| 31 | MSI:</strong> The Windows Installer engine expects to call a LoadLibrary and | ||
| 32 | GetProcAddress on the custom action DLL, so an unmanaged DLL needs to implement | ||
| 33 | the function that is initially called by MSI and ultimately returns the result. | ||
| 34 | This function acts as a proxy to relay the custom action call into the | ||
| 35 | managed custom action assembly, and relay the result back to the caller. </p> | ||
| 36 | <li><strong>Providing supporting assemblies without | ||
| 37 | requiring them to be installed as files:</strong> If a DLL custom | ||
| 38 | action runs before the product's files are installed, then it is difficult | ||
| 39 | to provide any supporting files, because of the way the CA DLL is singly | ||
| 40 | extracted and executed from a temp file. (This can be a problem for | ||
| 41 | unmanaged CAs as well.) With managed custom actions we have already hit | ||
| 42 | that problem since both the CA assembly and the MSI wrapper assembly | ||
| 43 | need to be loaded. To solve this, the proxy DLL carries an appended | ||
| 44 | cab package. When invoked, it will extract all contents of the | ||
| 45 | cab package to a temporary working directory. This way the cab package can | ||
| 46 | carry any arbitrary dependencies the custom action may require.</li> | ||
| 47 | <li><p><strong>Hosting and configuring the Common Language Runtime:</strong> | ||
| 48 | In order to invoke a method in a managed assembly from a previously | ||
| 49 | unmanaged process, the CLR needs to be "hosted". This involves choosing | ||
| 50 | the correct version of the .NET Framework to use out of the available | ||
| 51 | version(s) on the system, binding that version to the current process, and | ||
| 52 | configuring it to load assemblies from the temporary working directory.</p> | ||
| 53 | <li><p><strong>Converting the integer session handle into a | ||
| 54 | Session object:</strong> The <a href="">Session</a> class in the managed | ||
| 55 | wrapper library has a constructor which takes an integer session handle as | ||
| 56 | its parameter. So the proxy simply instantiates this object before | ||
| 57 | calling the real CA function.</p> | ||
| 58 | </ol> | ||
| 59 | <p>The unmanaged CAPack module, when used in combination with the managed proxy in | ||
| 60 | the | ||
| 61 | Microsoft.WindowsInstaller assembly, accomplishes the tasks above to enable | ||
| 62 | fully-functional managed DLL custom actions.</p> | ||
| 63 | <p><br/></p> | ||
| 64 | <p><b>See also:</b></p> | ||
| 65 | <ul> | ||
| 66 | <li><a href="writingcas.htm">Writing Managed Custom Actions</a></li> | ||
| 67 | <li><a href="caconfig.htm">Writing the CustomAction.config file</a></li> | ||
| 68 | <li><a href="samplecas.htm">Sample C# Custom Actions</a></li> | ||
| 69 | <li><a href="buildingcas.htm">Building Managed Custom Actions</a></li> | ||
| 70 | </ul> | ||
| 71 | <p><br/></p> | ||
| 72 | </div> | ||
| 73 | </body> | ||
| 74 | </html> | ||