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3 <title>Writing Managed Custom Actions</title>
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9
10 <div id="control">
11 <span class="productTitle">Deployment Tools Foundation</span><br />
12 <span class="topicTitle">Writing Managed Custom Actions</span><br />
13 <div id="toolbar">
14 <span id="chickenFeet">
15 <a href="using.htm">Development Guide</a> &gt;
16 <a href="managedcas.htm">Managed CAs</a> &gt;
17 <span class="nolink">Writing CAs</span>
18 </span>
19 </div>
20 </div>
21 <div id="main">
22 <div id="header">
23 </div>
24 <div class="summary">
25 <p><b>Caveats</b></p>
26 <p>Before choosing to write a custom action in managed code instead of
27 traditional native C++ code, you should carefully consider the following:</p>
28 <ul>
29 <li><p>Obviously, it introduces a dependency on the .NET Framework. Your
30 MSI package should probably have a LaunchCondition to check for the presence
31 of the correct version of the .NET Framework before anything else happens.</p></li>
32 <li><p>If the custom action runs at uninstall time, then even the uninstall of
33 your product may fail if the .NET Framework is not present. This means a
34 user could run into a problem if they uninstall the .NET Framework before
35 your product.</p></li>
36 <li><p>A managed custom action should be configured to run against a specific
37 version of the .NET Framework, and that version should match the version your
38 actual product runs against. Allowing the version to "float" to the latest
39 installed .NET Framework is likely to lead to compatibility problems with
40 future versions. The .NET Framework provides side-by-side functionality for
41 good reason -- use it.</p></li>
42
43 </ul>
44 <p><br/></p>
45 <p><b>How To</b></p>
46 <ul>
47 <li><p>A custom action function needs to be declared as
48 <tt>public static</tt> (aka <tt>Public Shared</tt> in VB.NET). It takes one parameter which is
49 a <a href="DTFAPI.chm::/html/T_Microsoft_Deployment_WindowsInstaller_Session.htm">Session</a> object, and returns a
50 <a href="DTFAPI.chm::/html/T_Microsoft_Deployment_WindowsInstaller_ActionResult.htm">ActionResult</a> enumeration.</p>
51 <pre><font face="Consolas, Courier New"> [CustomAction]
52 <font color=blue>public</font> <font color=blue>static</font> ActionResult MyCustomAction(Session session)</font></pre><br />
53 <li><p>The function must have a
54 <a href="DTFAPI.chm::/html/T_Microsoft_Deployment_WindowsInstaller_CustomActionAttribute.htm"
55 >CustomActionAttribute</a>, which enables it to be
56 linked to a proxy function. The attribute can take an optional
57 &quot;name&quot; parameter, which is the name of the entrypoint
58 that is exported from the custom action DLL.</p>
59 <li><p>Fill in MSI CustomAction table entries just like you
60 would for a normal type 1 native-DLL CA. Managed CAs can also work just
61 as well in deferred, rollback, and commit modes.</p>
62 <li><p>If the custom action function throws any kind of
63 Exception that isn't handled internally, then it will be caught by the proxy
64 function. The Exception message and stack trace will be printed to the
65 MSI log if logging is enabled, and the CA will return a failure code.</p>
66 <li><p>To be technically correct, any MSI handles obtained should be
67 closed before a custom action function exits -- otherwise a warning
68 gets printed to the log. The handle classes in the managed library
69 (<a href="DTFAPI.chm::/html/T_Microsoft_Deployment_WindowsInstaller_Database.htm">Database</a>,
70 <a href="DTFAPI.chm::/html/T_Microsoft_Deployment_WindowsInstaller_View.htm">View</a>,
71 <a href="DTFAPI.chm::/html/T_Microsoft_Deployment_WindowsInstaller_Record.htm">Record</a>,
72 <a href="DTFAPI.chm::/html/T_Microsoft_Deployment_WindowsInstaller_SummaryInfo.htm">SummaryInfo</a>)
73 all implement the IDisposable interface,
74 which makes them easily managed with C#'s <tt>using</tt>
75 statement. Alternatively, they can be closed in a finally block.
76 As a general rule, <i>methods</i> return new handle objects that should be
77 managed and closed by the user code, while <i>properties</i> only return a reference
78 to a prexisting handle object.</p></li>
79 <li><p>Don't forget to use a <a href="caconfig.htm">CustomAction.config</a> file to
80 specify what version of the .NET Framework the custom action should run against.</p></li>
81 </ul>
82
83 <p><br/></p>
84 <p><b>See also:</b></p>
85 <ul>
86 <li><a href="samplecas.htm">Sample C# Custom Actions</a></li>
87 <li><a href="caconfig.htm">Specifying the Runtime Version</a></li>
88 <li><a href="databases.htm">Working with MSI Databases</a></li>
89 <li><a href="buildingcas.htm">Building Managed Custom Actions</a></li>
90 <li><a href="debuggingcas.htm">Debugging Managed Custom Actions</a></li>
91 </ul>
92 <p><br/></p>
93
94 </div>
95
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