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    <h1>key property</h1>

        <section class="multi-line-signature">
          <span class="returntype">Key</span>
          <span class="name ">key</span>
          <div class="features">final, inherited</div>
        </section>
        <section class="desc markdown">
          <p>Controls how one widget replaces another widget in the tree.</p>
<p>If the <code>runtimeType</code> and <code>key</code> properties of the two widgets are
<code>operator==</code>, respectively, then the new widget replaces the old widget by
updating the underlying element (i.e., by calling <code>Element.update</code> with the
new widget). Otherwise, the old element is removed from the tree, the new
widget is inflated into an element, and the new element is inserted into the
tree.</p>
<p>In addition, using a <code>GlobalKey</code> as the widget's <code>key</code> allows the element
to be moved around the tree (changing parent) without losing state. When a
new widget is found (its key and type do not match a previous widget in
the same location), but there was a widget with that same global key
elsewhere in the tree in the previous frame, then that widget's element is
moved to the new location.</p>
<p>Generally, a widget that is the only child of another widget does not need
an explicit key.</p>
<p>See also the discussions at <code>Key</code> and <code>GlobalKey</code>.</p>
        </section>
                <section class="summary source-code" id="source">
          <h2><span>Implementation</span> </h2>
          <pre class="language-dart"><code class="language-dart">final Key key

</code></pre>
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