Angular 4-错误:formControlName必须与父formGroup指令一起使用

我正在使用组件-

engine-add-contact-form.html

<form (ngSubmit)="onSubmit()" [formGroup]="contact_form">
<md-tab-group>
    <md-tab label="Form">
        <ang-form></ang-form>
    </md-tab>
    <md-tab label="Email">
        <ang-email></ang-email>
    </md-tab>
    <md-tab label="Message">
        <ang-message></ang-message>
    </md-tab>
</md-tab-group>
<button md-raised-button type="submit">Publish</button>

ang-form.html

<div class="form-grid form-title">
     <md-input-container>
         <input formControlName="contact_form_title" 
        class="form-title-field" mdInput placeholder="Title" value="">
     </md-input-container>
</div>

使用与我添加其他组件(ang-email ang-message)html相同的方法.

Using same way i added other components (ang-email ang-message) html.

我在engine-add-form.ts

export class EngineAddFormComponent{

contact_form: any;

form_value: any;

constructor(){
    this.contact_form = new FormGroup({
        contact_form_title: new FormControl('', Validators.minLength(2)),
        ........
        ........
    });
}
onSubmit(){
    this.form_value = JSON.stringify(this.contact_form.value);
    console.log(this.form_value);
}
}

我收到以下错误-

错误:formControlName必须与父formGroup指令一起使用. 您将要添加一个formGroup 指令并将其传递给现有的FormGroup实例(您可以在您的类中创建一个实例).

Error: formControlName must be used with a parent formGroup directive. You'll want to add a formGroup directive and pass it an existing FormGroup instance (you can create one in your class).

我不明白我的代码出了什么问题.

I can't understand what is wrong with my code.