parameter-name">onValue</span>(<span class="parameter" id="onValue-param-value"><span class="type-annotation">T</span> <span class="parameter-name">value</span></span>), {</span> <span class="parameter" id="then-param-onError"><span class="type-annotation"><a href="dart-core/Function-class.html">Function</a></span> <span class="parameter-name">onError</span></span> })
            <span class="returntype parameter">&#8594; <a href="dart-async/Future-class.html">Future</a><span class="signature">&lt;<wbr><spa