flutter 自定义字体 


fonts:
    - family: PingFangExtraLight
      fonts:
        - asset: fonts/PingFang/PingFang-ExtraLight.ttf
    - family: PingFangHeavy
      fonts:
        - asset: fonts/PingFang/PingFang-Heavy.ttf
    - family: PingFangLight
      fonts:
        - asset: fonts/PingFang/PingFang-Light.ttf
    - family: PingFangMedium
      fonts:
        - asset: fonts/PingFang/PingFang-Medium.ttf
    - family: PingFang
      fonts: