title: Typescript: _this2.onClick is not a function
body: <p>I use typescript for react-native development.
  Here <code>List</code> and <code>ListItem</code> are from NativeBase and <code>ListItem</code> is like <code>TouchableOpacity</code> component.</p>
  
  <pre><code>...
  public onClick = () =&gt; this.props.navigation.navigate("NextScreen");
  public _renderRow = (item: any) {
      return (
          &lt;ListItem onPress={() =&gt; this.onClick()}&gt;
               ...
          &lt;/ListItem&gt;
      );
  }
  public render() {
     return(
          &lt;List
              dataArray={this.data}
              renderRow={this._renderRow}
          /&gt;
     );
  }
  </code></pre>
  
  <p>When I click item, it shows following error.</p>
  
  <blockquote>
    <p>_this2.onClick is not a function. (In '_this2.onClick()', '_this2.onClick' is undefined)</p>
  </blockquote>
  
  <p>I assume this is because <code>onClick()</code> function isn't bound to component class. Is the function bound automatically in typescript?</p>
  
  <p>How can I solve this problem?</p>