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How to: Ignore errors in tasks

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Sometimes you want a build to be tolerant of faults in certain tasks. If those non-critical tasks fail, you want the build to continue because it can still produce the required output. For example, if a project uses a SendMail task to send an e-mail message after each component is built, you might consider it acceptable for the build to proceed to completion even when the mail servers are unavailable and the status messages cannot be sent. Or, for example, if intermediate files are usually deleted during the build, you might consider it acceptable for the build to proceed to completion even when those files cannot be deleted.

Use the ContinueOnError attribute

The ContinueOnError attribute of the Task element controls whether a build stops or continues when a task failure occurs. This attribute also controls whether errors are treated as errors or warnings when the build continues.

The ContinueOnError attribute can contain one of the following values:

  • WarnAndContinue or true. When a task fails, subsequent tasks in the Target element and the build continue to execute, and all errors from the task are treated as warnings.

  • ErrorAndContinue. When a task fails, subsequent tasks in the Target element and the build continue to execute, and all errors from the task are treated as errors.

  • ErrorAndStop or false (default). When a task fails, the remaining tasks in the Target element and the build aren't executed, and the entire Target element and the build is considered to have failed.

Versions of the .NET Framework before 4.5 supported only the true and false values.

The default value of ContinueOnError is ErrorAndStop. If you set the attribute to ErrorAndStop, you make the behavior explicit to anyone who reads the project file.

To ignore an error in a task

Use the ContinueOnError attribute of the task. For example:

<Delete Files="@(Files)" ContinueOnError="WarnAndContinue"/>

Example

The following code example illustrates that the Build target still runs and the build is considered a success, even if the Delete task fails.

<Project DefaultTargets="FakeBuild"
    xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
    <ItemGroup>
        <Files Include="*.obj"/>
    </ItemGroup>
    <Target Name="Clean">
        <Delete Files="@(Files)" ContinueOnError="WarnAndContinue"/>
    </Target>

    <Target Name="FakeBuild" DependsOnTargets="Clean">
        <Message Text="Building after cleaning..."/>
    </Target>
</Project>

See also