add 下拉逻辑 review by daiqiang

@@ -38,6 +38,7 @@ export default class AssociatorGift extends Component {
         let heightStyle = total > 0 ? {height: 45} : {height: 35};
         return (
             <View style={styles.bagBackground}>
+                <View style={styles.header}/>
                 <Image style={styles.bgImage} source={require('../images/hyzx_lb.png')}/>
                 <Text style={styles.bagTitle}>{title}</Text>
                 <Text style={[styles.bagTips, heightStyle]}>{desc}</Text>
@@ -143,10 +144,20 @@ let styles = StyleSheet.create({
     container: {
         flex: 1,
     },
+    header: {
+      backgroundColor: '#444444',
+      width,
+      height: 500,
+      flex: 1,
+      position: 'absolute',
+      top: -500,
+      left: 0,
+    },
     bagBackground: {
         width: width,
         alignItems: 'center',
         backgroundColor: '#444444',
+        position: 'relative'
     },
     bgImage: {
         width: 50,