如何修复angular7中的“无法读取未定义的属性”错误”？

Question

Material Validation

Quantity is required

    <div *ngIf="quantity.errors.minlength">should be greater than one</div>

I expect that the quantity field should validate only integers no decimal and it should be greater than one.

Answer 1

如果是被动式，可以尝试一下

*ngIf="form.get('quantity').hasError('minlength')"

Answer 2

You can use ? in property binding:

<div *ngIf="quantity?.errors.minlength">should be greater than one</div>

This won't throw any errors for not having any errors on quantity. and when any errors are bound to quantity the message will show up.