如何为 Picker 提供默认的“请选择..."；选项? [英] How to provide Picker a default "Please select..." option?

问题描述

我想让我的 Picker 在启动时显示默认选项".这意味着:类似于请选择一个选项".

I'd like to make my Picker to show a "default option" on startup. That means: something like "Please select an option".

我尝试用这个短语手动添加一个选项，但是，这样可以在选择其他选项后重新选择默认选项"，就像它是真正的选项之一.有没有办法做到这一点?

I've tried to add a option manually with this phrase, but, this way the "default option" can be re-selected after selecting other options, like it was one of the real options. There is some way to do this?

<View style={Styles.row}>
            <Picker
                selectedValue={this.state.initialOption}
                onValueChange={this.handleChangeOption}
                prompt='Options'}
              >
              <Picker.Item label='Please select an option...' value='0' />
              <Picker.Item label='option 1' value='1' />
              <Picker.Item label='option 2' value='2' />
            </Picker>
</View>

推荐答案

您可以向 handleChangeOption 添加条件，以便它仅在值不为 0 时设置状态(请选择一个选项... 选择器).类似的东西:

You can add a conditional to your handleChangeOption so that it would only set state when the value is not 0 (the Please select an option... Picker). Something like:

handleChangeOption(val) {
  if (val !== 0) {
    this.setState({selectedValue: val});
  }
}

...
  
 <View style={Styles.row}>
    <Picker
       selectedValue={this.state.selectedValue}
       onValueChange={this.handleChangeOption}
       prompt='Options'}
       >
       <Picker.Item label='Please select an option...' value='0' />
       <Picker.Item label='option 1' value='1' />
       <Picker.Item label='option 2' value='2' />
    </Picker>
</View>

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