Try ViewHelper

Attempts to render child content. If an Exception is encountered while rendering, instead the f:else child node is rendered, if it is present. If f:else is not used, no output is returned.

Can be used to perform complex translations of Exception messages which can occur. Can naturally also be used to provide a great deal of additional information about every possible Exception-type error which Fluid can encounter (and there are many).

Note that this is a Condition ViewHelper which means you can use the f:then child node but it differs from regular Conditions by also allowing the template developer to skip the f:then child node and use the direct tag content as the "TRUE" condition and add an f:else which is only rendered in case of an Exception during rendering.

Also note that you can use the then and else attributes; the then attribute is what is attempted rendered and the else attribute is what is rendered if retrieving the then attribute's value fails. Which clearly only makes sense if for example complex inline ViewHelpers are used in the attributes.

Example usage

Please note that this is a theoretical example!

The example is theoretical in one major aspect: v:format.json.decode throws an Exception which Fluid displays as a string always - abstract from this and imagine that a plain Exception happens on errors.

<v:try>
    <!-- assume that the variable {badJson} contains the string "DontDecodeMe"
         which if course is invalid JSON and cannot be decoded. The default
         behavior is to simply output a simple "cannot decode" string. -->
    <v:variable.set name="decodedBadJson" value="{badJson -> v:format.json.decode()}" />
    Displayed only if the JSON decode worked. Much more code and many more
    ViewHelpers can go here. Now, imagine that this block spans so much code
    that potentially there could come an Exception from many additional places
    (for example from Widgets) and you cannot be sure where the Exception comes
    from but still want to tell the user what exactly went wrong and provide
    an error code which makes sense to send to developers if problems persist:
    <f:else>
        <h4>
            Error in "{exception.trace.0.class
                -> v:iterator.explode(glue: '_')
                -> v:iterator.pop()
                -> v:format.replace(substring: 'ViewHelper', replacement: ''}"
            <small>{exception.code}</small>
            <!-- Output example: "Error in Decode <small>1358440054</small>" -->
        </h4>
        <p>
            {exception.message}
            <!-- Output example: "The provided argument is invalid JSON" -->
        </p>
        <pre>
            Value: ``{exception.trace.0.args.0}
            <!-- Output example: "Value: ``DontDecodeMe" which is quite nice
                 for developers to know as part of a bug report from users. -->
        </pre>
    </f:else>
</v:try>
...or if you want a shorter version...
<!-- Tries to encode an object, if it fails, falls back by returning a proper JSON
     value, thus preventing breakage by the JSON consumer whatever it may be. -->
{v:try(then: '{badObject -> v:format.json.encode()}', else: '{"validJson": "validValue"')}
<!-- Note: be VERY careful about the inline JSON syntax! It's very close to Fluids. Always
     double quote your object variables' names, that prevents almost all issues! -->