title: How to set the input of a combobox to read-only
body: <p>In one of my UI5-Dialogs, I implemented a combobox which is invisible when the screen is initially loaded.
  In the method <code>onAfterRendering</code>, I start with setting the input to read-only:</p>
  
  <pre class="lang-js prettyprint-override"><code>onAfterRendering: function(oEvent) {
    var oShovel = this.getView("View0200").byId("comboShovel");
    oShovel.$().find("input").attr("readonly", true);
    this.setVisibleByListKey();
  },
  </code></pre>
  
  <p>After this the method <code>setVisibleByListKey</code> is called, the property <code>visibleShovel</code> will be set to false.</p>
  
  <pre class="lang-js prettyprint-override"><code>setVisibleByListKey: function(oEvent) {
    var oModel = this.getView("View0200").getModel("Data0200");
    this.setVisibleByListKey1(oModel);
    // ...
  },
  
  setVisibleByListKey1: function(oModel) {
    oModel.setProperty("/visibleShovel", false);
  },
  </code></pre>
  
  <p>The property is bound to the attribute visible on my combobox.
  Because of this behavior, the method <code>onAfterRendering</code> will be called again, the attribute <code>readonly</code> is not available (because of invisibility).</p>
  
  <pre class="lang-xml prettyprint-override"><code>&lt;ComboBox id="comboShovel"
    editable="true"
    enabled="true"
    visible="{Data0200&gt;/visibleShovel}"
    valueState="None"
    change=".changeCombo"&gt;
    &lt;items&gt;
      &lt;core:Item text="Ja" enabled="true" key="0" /&gt;
      &lt;core:Item text="Nein" enabled="true" key="1" /&gt;
      &lt;core:Item text="Nicht erforderlich" enabled="true" key="2" /&gt;
    &lt;/items&gt;
  &lt;/ComboBox&gt;
  </code></pre>
  
  <p>I tried to call the set method in <code>onInit</code> or <code>onBeforeRendering</code> but at this time the input attributes can not be changed (because of invisibility again).</p>
  
  <p>So how can I set the input of the combobox to read-only when I set the named visible property?</p>