midButton ios不显示 安卓能显示

"tabBar": {
"color": "#7A7E83",
"selectedColor": "#4a86f4",
"borderStyle": "black",
"backgroundColor": "#ffffff",
"iconWidth": "24px",
"list": [{
"pagePath": "pages/indexpages/workspace/workspace",
"text": "工作台",
"iconPath": "static/images/Project.png",
"selectedIconPath": "static/images/Project-active.png"
},
{
"pagePath": "pages/indexpages/systemcenter/systemcenter",
"text": "个人中心",
"iconPath": "static/images/mycenter.png",
"selectedIconPath": "static/images/mycenter-active.png"
}
],
"midButton": {
"width": "70px",
"height": "70px",
"iconPath": "static/images/tab-mid.png",
"iconWidth": "54px",
"text": "添加项目"
}
},