title: Uncaught TypeError: Cannot read property 'setVisible' of undefined
body: <p>Im fairly new to SAPUI5 and when I click on button I get the error in the title 
  what I did in Is I used the SAP web IDE to create new MVC project .</p>
  
  <p>in the main view JS I put </p>
  
  <pre><code>createContent : function(oController) {
      var btn = new sap.m.Button({
              id:"myBtn",
              text : "Content Button"
         });
      return new sap.m.Page({
          title: "TitleT",
          content: [ btn ]
      });
  }
  </code></pre>
  
  <p>in the Main controller JS I put the following code</p>
  
  <pre><code>onInit: function() {
      var that = this;
      window.setTimeout(function() {
          that.byId("myBtn").setVisible(true);
      }, Math.random() * 10000);
  },
  
  onPress: function() {
      this.byId("pressMeButton").setText("I got pressed");
  }
  </code></pre>
  
  <p>When I run it I see the button but when I click on it I get the error in the on Init,
  what am I doing wrong here?</p>