Mapbox案例表达 [英] Mapbox case expression

问题描述

我尝试使用大小写表达式来设置地图框图层的样式:

i try to style my mapbox layer using case expression:

const max_expr = ['max', ['get', 'POLY_COLOUR_CODE_D'], ['get', 'POLY_COLOUR_CODE_BW'], ['get', 'POLY_COLOUR_CODE_A']];

'paint': {
        'fill-color': ['case', ['==', max_expr, 1], 'green', ['==', max_expr, 2],  'yellow', 
        ['==', max_expr, 3], 'red', ['==', max_expr, 4], 'red']
}

但是我得到以下奇怪的错误:paint.fill-color:期望参数的数量为奇数. 您知道如何解决此问题吗?

but i get following weird error: paint.fill-color: Expected an odd number of arguments. Do you have any idea how to fix this?

推荐答案

您可能只是在case表达式中缺少了默认值:

You are probably just missing a default value in your case expression:

[
  'case',
  ['==', max_expr, 1],
  'green',
  ['==', max_expr, 2],
  'yellow',
  ['==', max_expr, 3],
  'red',
  ['==', max_expr, 4],
  'red',
  <default>
];

这不是很明显，但是文档显示默认值不是可选的: https://www.mapbox.com/mapbox-gl-js/style-spec/#expressions-case

It's not super obvious, but the documentation shows that a default is not optional: https://www.mapbox.com/mapbox-gl-js/style-spec/#expressions-case

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