ngng自定义输入数字选择器中的零值

Question

我有问题

• 在服务器端PHP上，api返回json，其中某些项目的值为零。我在PHP端使用JSON_NUMERIC_CHECK。

• 在有角度的一面：

<app-number-picker name="scoreEq1" [(ngModel)]="match.scoreEq1" #score="ngModel"></app-number-picker> 

然后，我自定义了号码选择器组件：

<div class="input-group mb-3 input-md">
  <div class="input-group-prepend">
    <span class="input-group-text decrease" (click)="decrease();">-</span></div>
  <input [name]="name" [(ngModel)]="value" class="form-control counter" type="number" step="1">
  <div class="input-group-prepend">
    <span class="input-group-text increase" (click)="increase();" style="border-left: 0px;">+</span></div>
</div>

我的代码的灵感来自blog.thoughtram.io在组件ts中：

import { Component, Input, forwardRef } from '@angular/core';
import { ControlValueAccessor, NG_VALUE_ACCESSOR } from '@angular/forms';

@Component({
  selector: 'app-number-picker',
  templateUrl: './numberPicker.component.html',
  styleUrls: ['./numberPicker.component.css'],
  providers: [
    {
      provide: NG_VALUE_ACCESSOR,
      useExisting: forwardRef(() => NumberPickerComponent),
      multi: true
    }
  ]
})
export class NumberPickerComponent implements ControlValueAccessor {

  @Input()
  name: string;
  @Input() val: number;
  // Both onChange and onTouched are functions
  onChange: any = () => { };
  onTouched: any = () => { };

  get value() {
    return this.val;
  }

  set value(val) {
    this.val = val;
    this.onChange(val);
    this.onTouched();
  }
  // We implement this method to keep a reference to the onChange
  // callback function passed by the forms API
  registerOnChange(fn) {
    this.onChange = fn;
  }
  // We implement this method to keep a reference to the onTouched
  // callback function passed by the forms API
  registerOnTouched(fn) {
    this.onTouched = fn;
  }
  // This is a basic setter that the forms API is going to use
  writeValue(value) {
    if (value) {
      this.value = value;
    }
  }

  decrease() {
    if (this.value === 0 || this.value === null) {
      this.value = null;
    } else {
      this.value--;
    }
  }

  increase() {
    if (isNaN(this.value) || this.value === null) {
      this.value = 0;
    } else {
      this.value++;
    }
  }

}

• 我的问题是match.scoreEq1 = 0 =>时此值未显示在我的输入中=>它保持空白！值为零时，似乎是“未定义”。

NB：match.scoreEq1可以为null =>在这种情况下，我想显示为空白

问题出在哪里？ ngModel？ ControlValueAccessor？

Answer 1

我猜是因为在writeValue(value)方法中您选中了if(value)，但是，如果您的值为0，则该值实际上为false，并且永远不会设置组件的值。只需替换if语句，如下所示：

writeValue(value) {
   if (value !== null && value !== undefined) {
     this.value = value;
   }
}