weui/navigation-bar/navigation-bar.wxml

<view class="weui-navigation-bar {{extClass}}">
  <view class="weui-navigation-bar__placeholder {{ios ? 'ios' : 'android'}}" style="padding-top: {{statusBarHeight}}px;visibility: hidden;"></view>
  <view class="weui-navigation-bar__inner {{ios ? 'ios' : 'android'}}" style="padding-top: {{statusBarHeight}}px; color: {{color}};background: {{background}};{{displayStyle}};{{innerPaddingRight}};{{innerWidth}};">

    <view class='weui-navigation-bar__left' style="{{leftWidth}}">
      <block wx:if="{{back}}">
        <view class="weui-navigation-bar__buttons">
          <view bindtap="back" class="weui-navigation-bar__button weui-navigation-bar__btn_goback"></view>
        </view>
      </block>
      <block wx:else>
        <slot name="left"></slot>
      </block>
    </view>

    <view class='weui-navigation-bar__center'>
      <view wx:if="{{loading}}" class="weui-navigation-bar__loading">
        <view class="weui-loading" style="width:{{size.width}}rpx;height:{{size.height}}rpx;"></view>
      </view>
      <block wx:if="{{title}}">
        <text>{{title}}</text>
      </block>
      <block wx:else>
        <slot name="center"></slot>
      </block>
    </view>

    <view class='weui-navigation-bar__right'>
      <slot name="right"></slot>
    </view>
  </view>
</view>