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<div class="inner-content">
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<h1>
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Helper Per Binding Bidirezionali
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<a class="edit-page-link" href="https://github.com/facebook/react/tree/master/docs/docs/10.2-form-input-binding-sugar.it-IT.md" target="_blank">Edit on GitHub</a>
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</h1>
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<div class="subHeader"></div>
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<p><code>ReactLink</code> è una maniera semplice di esprimere binding bidirezionali con React.</p>
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<blockquote>
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<p>Nota:</p>
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<p>Se hai poca esperienza del framework, nota che <code>ReactLink</code> non è necessario per molte applicazioni e dovrebbe essere utilizzato con cautela.</p>
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</blockquote>
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<p>In React, i dati fluiscono in una direzione: dal proprietario ai figli. Questo poiché i dati fluiscono in una sola direzione nel <a href="https://en.wikipedia.org/wiki/Von_Neumann_architecture">modello di computazione di Von Neumann</a>. Puoi pensare ad esso come "binding unidirezionale dei dati."</p>
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<p>Tuttavia, esistono parecchie applicazioni che richiedono di leggere dati e farli fluire nuovamente nel tuo programma. Ad esempio, quando sviluppi dei moduli, vorrai spesso aggiornare uno <code>state</code> di React quando ricevi un input dall'utente. O forse vuoi effettuare il layout in JavaScript e reagire ai cambiamenti nelle dimensioni di alcuni elementi DOM.</p>
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<p>In React, questo verrebbe implementato ascoltando un evento "change", leggendo la tua fonte di dati (solitamente il DOM) e chiamando <code>setState()</code> su uno dei tuoi componenti. "Chiudere il ciclo del flusso dei dati" esplicitamente conduce a programmi più comprensibili e mantenibili. Consulta <a href="/react/docs/forms.html">la nostra documentazione sui moduli</a> per maggiori informazioni.</p>
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<p>Il binding bidirezionale -- assicurarsi implicitamente che alcuni valori nel DOM siano sempre consistenti con degli <code>state</code> in React -- è più conciso e supporta un'ampia varietà di applicazioni. Abbiamo fornito <code>ReactLink</code>: zucchero sintattico per impostare il pattern del ciclo del flusso di dati descritto in predecenza, ovvero "collegare" una fonte di dati con lo <code>state</code> di React.</p>
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<blockquote>
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<p>Nota:</p>
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<p><code>ReactLink</code> è soltanto uno strato di astrazione e convenzioni attorno al pattern <code>onChange</code>/<code>setState()</code>. Non cambia fondamentalmente la maniera in cui i dati fluiscono all'interno della tua applicazione React.</p>
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</blockquote>
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<h2><a class="anchor" name="reactlink-prima-e-dopo"></a>ReactLink: Prima e Dopo <a class="hash-link" href="#reactlink-prima-e-dopo">#</a></h2>
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<p>Ecco un semplice esempio di modulo che non utilizza <code>ReactLink</code>:</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">NoLink</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span>
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<span class="nx">getInitialState</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
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<span class="k">return</span> <span class="p">{</span><span class="nx">message</span><span class="o">:</span> <span class="s1">'Ciao!'</span><span class="p">};</span>
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<span class="p">},</span>
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<span class="nx">handleChange</span><span class="o">:</span> <span class="kd">function</span><span class="p">(</span><span class="nx">event</span><span class="p">)</span> <span class="p">{</span>
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<span class="k">this</span><span class="p">.</span><span class="nx">setState</span><span class="p">({</span><span class="nx">message</span><span class="o">:</span> <span class="nx">event</span><span class="p">.</span><span class="nx">target</span><span class="p">.</span><span class="nx">value</span><span class="p">});</span>
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<span class="p">},</span>
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<span class="nx">render</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
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<span class="kd">var</span> <span class="nx">message</span> <span class="o">=</span> <span class="k">this</span><span class="p">.</span><span class="nx">state</span><span class="p">.</span><span class="nx">message</span><span class="p">;</span>
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<span class="k">return</span> <span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="s2">"text"</span> <span class="nx">value</span><span class="o">=</span><span class="p">{</span><span class="nx">message</span><span class="p">}</span> <span class="nx">onChange</span><span class="o">=</span><span class="p">{</span><span class="k">this</span><span class="p">.</span><span class="nx">handleChange</span><span class="p">}</span> <span class="o">/></span><span class="p">;</span>
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<span class="p">}</span>
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<span class="p">});</span>
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</code></pre></div>
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<p>Ciò funziona molto bene e il flusso di dati è molto chiaro. Tuttavia, in presenza di un gran numero di campi del modulo può risultare assai prolisso. Utilizziamo <code>ReactLink</code> per risparmiarci la scrittura di un po' di codice:</p>
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<div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">WithLink</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span>
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<span class="hll"> <span class="nx">mixins</span><span class="o">:</span> <span class="p">[</span><span class="nx">React</span><span class="p">.</span><span class="nx">addons</span><span class="p">.</span><span class="nx">LinkedStateMixin</span><span class="p">],</span>
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</span> <span class="nx">getInitialState</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
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<span class="k">return</span> <span class="p">{</span><span class="nx">message</span><span class="o">:</span> <span class="s1">'Ciao!'</span><span class="p">};</span>
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<span class="p">},</span>
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<span class="nx">render</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
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<span class="hll"> <span class="k">return</span> <span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="s2">"text"</span> <span class="nx">valueLink</span><span class="o">=</span><span class="p">{</span><span class="k">this</span><span class="p">.</span><span class="nx">linkState</span><span class="p">(</span><span class="s1">'message'</span><span class="p">)}</span> <span class="o">/></span><span class="p">;</span>
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</span> <span class="p">}</span>
|
|
<span class="p">});</span>
|
|
</code></pre></div>
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<p><code>LinkedStateMixin</code> aggiunge un metodo chiamato <code>linkState()</code> al tuo componente React. <code>linkState()</code> restituisce un oggetto <code>ReactLink</code> contenente il valore attuae dello stato React e una callback per cambiarlo.</p>
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<p>Gli oggetti <code>ReactLink</code> possono essere passati su e giù nell'albero come proprietà, quindi è facile (ed esplicito) impostare un binding bidirezionale tra un componente in profondità nella gerarchia e dello stato che si trova più in alto nella gerarchia.</p>
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<p>Nota che i checkbox hanno un comportamento speciale riguardo il loro attributo <code>value</code>, che è il valore che sarà inviato all'inoltro del modulo se il checkbox è spuntato (il valore predefinito è <code>on</code>). L'attributo <code>value</code> non è aggiornato quando il checkbox viene spuntato o deselezionato. Per i checkbox occorre usare <code>checkedLink</code> anziché <code>valueLink</code>:
|
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<code>
|
|
<input type="checkbox" checkedLink={this.linkState('booleanValue')} />
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</code></p>
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<h2><a class="anchor" name="dietro-le-quinte"></a>Dietro le Quinte <a class="hash-link" href="#dietro-le-quinte">#</a></h2>
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<p>Ci sono due ambiti in <code>ReactLink</code>: il posto in cui crei l'istanza di <code>ReactLink</code> e il posto in cui la utilizzi. Per dimostrare quanto sia semplice usare <code>ReactLink</code>, riscriviamo ciascun ambito separatamente perché sia più esplicito.</p>
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<h3><a class="anchor" name="reactlink-senza-linkedstatemixin"></a>ReactLink Senza LinkedStateMixin <a class="hash-link" href="#reactlink-senza-linkedstatemixin">#</a></h3><div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">WithoutMixin</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span>
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<span class="nx">getInitialState</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
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|
<span class="k">return</span> <span class="p">{</span><span class="nx">message</span><span class="o">:</span> <span class="s1">'Ciao!'</span><span class="p">};</span>
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<span class="p">},</span>
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<span class="hll"> <span class="nx">handleChange</span><span class="o">:</span> <span class="kd">function</span><span class="p">(</span><span class="nx">newValue</span><span class="p">)</span> <span class="p">{</span>
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</span><span class="hll"> <span class="k">this</span><span class="p">.</span><span class="nx">setState</span><span class="p">({</span><span class="nx">message</span><span class="o">:</span> <span class="nx">newValue</span><span class="p">});</span>
|
|
</span><span class="hll"> <span class="p">},</span>
|
|
</span> <span class="nx">render</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
|
|
<span class="hll"> <span class="kd">var</span> <span class="nx">valueLink</span> <span class="o">=</span> <span class="p">{</span>
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</span><span class="hll"> <span class="nx">value</span><span class="o">:</span> <span class="k">this</span><span class="p">.</span><span class="nx">state</span><span class="p">.</span><span class="nx">message</span><span class="p">,</span>
|
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</span><span class="hll"> <span class="nx">requestChange</span><span class="o">:</span> <span class="k">this</span><span class="p">.</span><span class="nx">handleChange</span>
|
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</span><span class="hll"> <span class="p">};</span>
|
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</span> <span class="k">return</span> <span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="s2">"text"</span> <span class="nx">valueLink</span><span class="o">=</span><span class="p">{</span><span class="nx">valueLink</span><span class="p">}</span> <span class="o">/></span><span class="p">;</span>
|
|
<span class="p">}</span>
|
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<span class="p">});</span>
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</code></pre></div>
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<p>Come puoi vedere, gli oggetti <code>ReactLink</code> sono semplici oggetti che hanno due proprietà: <code>value</code> e <code>requestChange</code>. <code>LinkedStateMixin</code> è altrettanto semplice: popola semplicemente questi campi con un valore da <code>this.state</code> e una callback che invoca <code>this.setState()</code>.</p>
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<h3><a class="anchor" name="reactlink-senza-valuelink"></a>ReactLink Senza valueLink <a class="hash-link" href="#reactlink-senza-valuelink">#</a></h3><div class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="kd">var</span> <span class="nx">WithoutLink</span> <span class="o">=</span> <span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span>
|
|
<span class="nx">mixins</span><span class="o">:</span> <span class="p">[</span><span class="nx">React</span><span class="p">.</span><span class="nx">addons</span><span class="p">.</span><span class="nx">LinkedStateMixin</span><span class="p">],</span>
|
|
<span class="nx">getInitialState</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="p">{</span><span class="nx">message</span><span class="o">:</span> <span class="s1">'Ciao!'</span><span class="p">};</span>
|
|
<span class="p">},</span>
|
|
<span class="nx">render</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
|
|
<span class="kd">var</span> <span class="nx">valueLink</span> <span class="o">=</span> <span class="k">this</span><span class="p">.</span><span class="nx">linkState</span><span class="p">(</span><span class="s1">'message'</span><span class="p">);</span>
|
|
<span class="kd">var</span> <span class="nx">handleChange</span> <span class="o">=</span> <span class="kd">function</span><span class="p">(</span><span class="nx">e</span><span class="p">)</span> <span class="p">{</span>
|
|
<span class="nx">valueLink</span><span class="p">.</span><span class="nx">requestChange</span><span class="p">(</span><span class="nx">e</span><span class="p">.</span><span class="nx">target</span><span class="p">.</span><span class="nx">value</span><span class="p">);</span>
|
|
<span class="p">};</span>
|
|
<span class="k">return</span> <span class="o"><</span><span class="nx">input</span> <span class="nx">type</span><span class="o">=</span><span class="s2">"text"</span> <span class="nx">value</span><span class="o">=</span><span class="p">{</span><span class="nx">valueLink</span><span class="p">.</span><span class="nx">value</span><span class="p">}</span> <span class="nx">onChange</span><span class="o">=</span><span class="p">{</span><span class="nx">handleChange</span><span class="p">}</span> <span class="o">/></span><span class="p">;</span>
|
|
<span class="p">}</span>
|
|
<span class="p">});</span>
|
|
</code></pre></div>
|
|
<p>La proprietà <code>valueLink</code> è anche abbastanza semplice. Gestisce semplicemente l'evento <code>onChange</code> e invoca <code>this.props.valueLink.requestChange()</code>, e inoltre utilizza <code>this.props.valueLink.value</code> anziché <code>this.props.value</code>. Tutto qua!</p>
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