如何在 Angular Material 9 中为“mat-select”元素编写自定义数据属性

Question

我正在尝试为 Angular Material 9 中的 mat-select 元素设置自定义数据属性 (data-tag)。以下是我正在使用的 HTML 和 TS 代码，但没有任何反应通过在浏览器中检查网页代码：

HTML：

<mat-form-field>
    <mat-label>Course</mat-label>
        <mat-select [formControl]="subjectControl" required>
            <mat-option>-- None --</mat-option>
            <mat-optgroup *ngFor="let course of subjects" [label]="course.semester" [disabled]="course.disabled">
                <mat-option *ngFor="let subject of course.courses" [value]="subject.subjectName" [attr.data-tag]="subject.subjectSemester">
                    {{ subject.subjectName }}
                </mat-option>
            </mat-optgroup>
        </mat-select>
</mat-form-field>

TS：

export interface SubjectGroup {
    disabled?: boolean;
    semester: string;
    courses: Subject[];
}
export interface Subject {
    subjectName: string;
    subjectSemester: string;
}

export class FormComponent implements OnInit {
    subjectControl = new FormControl("", Validators.required);
    subjects: SubjectGroup[] = [
        {
            semester: "Semester 1",
            courses: [
                {
                    subjectName: "Course 1",
                    subjectSemester: "1° Semester"
                },
                {
                    subjectName: "Course 2",
                    subjectSemester: "1° Semester"
                },
                {
                    subjectName: "Course 3",
                    subjectSemester: "1° Semester"
                },
                {
                    subjectName: "Course 4",
                    subjectSemester: "1° Semester"
                },
                {
                    subjectName: "Course 5",
                    subjectSemester: "1° Semester"
                }
            ]
        },
        {
            semester: "Semester 2",
            courses: [
                {
                    subjectName: "Course 1",
                    subjectSemester: "2° Semester"
                },
                {
                    subjectName: "Course 2",
                    subjectSemester: "2° Semester"
                },
                {
                    subjectName: "Course 3",
                    subjectSemester: "2° Semester"
                },
                {
                    subjectName: "Course 4",
                    subjectSemester: "2° Semester"
                }
            ]
        }
    ];
}

我找到了this question，但我不明白我做错了什么。谢谢

#编辑 1：

我也试过了：

<mat-option *ngFor="let subject of course.courses" [value]="subject.subjectName" [attr.data-tag]="subject ? subject.subjectSemester : null">

什么都没有……

Answer 1

终于解决了：

HTML：

<mat-form-field>
    <mat-label>Course</mat-label>
        <mat-select
            [formControl]="subjectControl"
            [attr.data-tag]="this.subjectControl.value"
            required
        >
            <mat-option>-- None --</mat-option>
            <mat-optgroup *ngFor="let course of subjects" [label]="course.semester" [disabled]="course.disabled">
                <mat-option *ngFor="let subject of course.courses" [value]="subject.subjectName"><!--here I have to set [value] to `.subjectName` or `.subjectSemester` to show it into the `data-tag`-->
                    {{ subject.subjectName }}
                </mat-option>
            </mat-optgroup>
        </mat-select>
</mat-form-field>

正如代码的cmets中所写，我必须将[attr.data-tag]放入mat-select等于this.subjectControl.value，并将mat-option的[value]设置为等于要存储到[attr.data-tag]中的值.

Answer 2

您的代码在我看来是正确的。我尝试将它添加到现有的 stackblitz 示例中，它显示在 HTML 中。也许这将有助于弄清楚：

https://stackblitz.com/edit/angular-material-select-compare-with?embed=1&file=app/app.html

<mat-option class="mat-option ng-star-inserted" data-tag="Three" role="option" ng-reflect-value="[object Object]" tabindex="0" id="mat-option-29" aria-selected="false" aria-disabled="false">