r <code>catchError</code> call happens after this future
has completed with an error then the error is reported as unhandled error.
See the description on <a href="dart-async/Future-class.html">Future</a>.</p>
    </section>
    
    <section class="summary source-code" id="source">
      <h2><span>Implementation</span> </h2>
      <pre class="language-dart"><code class="language-dart">Future&lt;S&gt; then&lt;S&gt;(FutureOr&lt;S&gt; onValue(T value), {Function onError});</code></pre>
    </section>

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