更新消息列表分享 UI

 import React, { Component } from 'react';
 import {
   Text,
+  Image,
   View,
   Dimensions,
   StyleSheet,
@@ -19,7 +20,7 @@ function ShareButton(props) {
         props.shareAction && props.shareAction(props.rowData);
       }}
     >
-      <Text style={styles.shareButtonText}>去分享</Text>
+      <Image source={require('../../images/message_share.png')} style={styles.shareButtonImage}></Image>
     </TouchableOpacity>
   )
 }
@@ -139,16 +140,12 @@ let styles = StyleSheet.create({
     height: 14 
   },
   shareButton: {
-    width: 60,
-    height: 30,
-    borderRadius: 3,
-    backgroundColor: '#D0021B',
+    width: 15 * DEVICE_WIDTH_RATIO,
+    height: 15 * DEVICE_WIDTH_RATIO,
     justifyContent: 'center'
   },
-  shareButtonText: {
-    fontSize: 14,
-    color: 'white',
-    textAlign: 'center',
+  shareButtonImage: {
+    flex: 1
   }
 });