Wix 使用总结(续)--关于Feature和Component的状态判断安装过程

安装过程中，有时候需要根据用户的设置来进行不同的安装，其中一个方面就是根据用户选择安装的Feature或者Component，来判断下一步的操作。

    Wix中提供了相关的判断方法和内置的状态值。

    Prepending some special characters to the names will give them extra meaning:

    %  environment variable (name is case insensitive)

    $   action state of component

    ?   installed state of component

    &   action state of feature

    !   installed state of feature

    The last four can return the following integer values:

   -1   no action to be taken

   1   advertised (only for components)

   2   not present

   3   on the local computer

   4   run from the source

A few examples to make things clearer:

(&FeatureName = 3) AND NOT (!FeatureName = 3)

Run action only if the product will be installed locally. Do not run action on a reinstallation.

The term &FeatureName = 3 means the action is to install the feature locally.

The term NOT (!FeatureName = 3) means the feature is not installed locally.

 (&FeatureName = 2) AND (!FeatureName = 3)

Run action only if the feature will be uninstalled.

This condition only checks for a transition of the feature from an installed state of local to the absent state.

(?ComponentName = 3) AND ($ComponentName = 2 OR $ComponentName = 4)

Run action only if the component was installed locally, but is transitioning out of state.

The term ?ComponentName = 3 means the component is installed locally.

The term $ComponentName = 2 means that the action state on the component is absent.

The term $ComponentName = 4 means that the action state on the component is run from source. Note that an action state of advertise is not valid for a component.

?ComponentName = $ComponentName

Run action only on the reinstallation of a component.