如何在Android上更改textColor即使在Android中？(How to change textColor on press Even in Android?)

 你的初始状态可能没有设置，所以this.state.cities实际上是空的。 
 
 在渲染函数中做这样的事情： 
 
render() {
  const options = ( this.state.cities || [] ).map( (city) => ( {
      value: city.name,
      label: city.id
  } );

  return (
    -- other components --

    { options.length ? (
        <Field name="city"
            label="Cidade"
            value={this.state.value}
            onChange={this.handleChange}
            options={options}
            component="select"
        />
      ) : null }

    -- other components --
  );
}
 
 ( this.state.cities || [] )将检查this.state.cities是否可用，否则它使用一个空数组。 
 
 
 更多细节：你的axios调用是异步的。 这意味着，React不会等待axios获取数据，而只是尝试渲染某些东西。 
 
 你的状态尚未设置（可能），因此你会得到这个错误。 

Your initial state might not be set, so this.state.cities is actually empty.
 
Do something like this in your render function:
 
render() {
  const options = ( this.state.cities || [] ).map( (city) => ( {
      value: city.name,
      label: city.id
  } );

  return (
    -- other components --

    { options.length ? (
        <Field name="city"
            label="Cidade"
            value={this.state.value}
            onChange={this.handleChange}
            options={options}
            component="select"
        />
      ) : null }

    -- other components --
  );
}
 
( this.state.cities || [] ) will check if this.state.cities is available, otherwise it uses an empty array.
 
 
A little more detail: Your axios call is asynchronous. That means, that React doesn't wait for axios to fetch your data but instead just tries to render something.
 
Your state has not been set (probably) and therefore you get this error.