angular5 动态设置表单验证规则

patchValue 方法和 setValue 方法只能改变表单的值，但是无法改变表单的验证规则，有时我们根据不同情况执行不同的校验规则，则用该方法
this.validateForm.get('key').setValidators(Validators.required);

示例如下：

.html

<form nz-form [formGroup]="validateForm" class="basicInfoCreateContent" (ngSubmit)="submitForm($event,validateForm.value)">
    <nz-form-item>
        <nz-form-control [nzSpan]="24">
            <input nz-input formControlName="name" maxlength="20" placeholder="请输入" (blur)="onBlur()">
            <nz-form-explain *ngIf="validateForm.get('name').dirty && validateForm.get('name').errors || validateForm.get('name').pending ">
                <ng-container *ngIf="validateForm.get('name').hasError('required')">
                名称不能为空！
                </ng-container>
                <ng-container *ngIf="validateForm.get('name').hasError('duplicated')">
                用户名已存在！
                </ng-container>
            </nz-form-explain>
        </nz-form-control>
    </nz-form-item>
</form>

.ts

export class BranchEdit {
    constructor(private message: NzMessageService, private fb: FormBuilder) {
        this.validateForm = this.fb.group({
            name: ['', [ Validators.required ]],    // 名称
        });
        console.log(this)
    };
    validateForm: FormGroup;
    onBlur(){
        this.validateForm.get('name').setErrors({ error: true, duplicated: true });
    }
}