30.3. Attribute Directives

In the previous two chapters, you learned about two of the three Angular directives---components and structural. You will now use data-binding to practice attribute directives. These change the appearance of a specific HTML element within the DOM.

30.3.1. Open the Lesson 3 Folder

Open VSCode and return to the angular-lc101-projects folder. Find lesson3/examples/src/app in the sidebar and open the skill-set.component.ts, skill-set.component.html, and skill-set.component.css files.

Access Angular lesson 3 in VSCode.

Open the terminal panel and navigate to the lesson3 examples folder. Also make sure that you are on the master branch.

$ git branch
   * master
   solutions
$ ls
   lesson1 lesson2 lesson3
$ cd lesson3
$ ls
   examples        exercises
$ cd examples

Once you are in the folder, enter npm install in the terminal, then run ng serve to launch the project.

You should see the following:

Attribute directives starting screen.

30.3.2. Update the Skill-Set Styling

Examine the code in the skill-set.component.css and skill-set.component.html files:

Examples

CSS

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h3 {
   text-align: center;
   text-decoration: underline;
}

.skills {
   color: green;
}

HTML

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<div class="skills">
   <h3>{{listHeading}}</h3>
   <ol>
      <li *ngFor="let skill of skills">{{skill}}</li>
   </ol>
   <hr>
   <h3>Copy of Skill List</h3>
   <ol>
      <li *ngFor="let skill of skills">{{skill}}</li>
   </ol>
   <hr>
   <p>Here is some practice text...</p>
</div>

Right now, there is an awful lot of green on the page, which is set by the skills class in the CSS file. Let's fix this with some attribute directives.

30.3.2.1. Inline Styling

To change the color and bullet type of the first list element, we could override the CSS instructions with some inline code:

<ol style="color: black" type="A">

However, we can use what we learned about data-binding to replace these hard-coded styles with variables:

<ol [style.color]="alternateColor" [type]="bulletType">

Ideas to note:

  1. Unlike the structural directives *ngFor and *ngIf, we can add more than one attribute directive to an HTML tag.

  2. The style attribute has different properties that can be assigned using dot notation. Examples include style.color and style.background. For properties with two-word labels, like text-align, the data-binding syntax accepts either hyphens or camel case (style.text-align or style.textAlign).

  3. The variables alternateColor and bulletType are assigned in the skill-set.component.ts file.

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    export class SkillSetComponent implements OnInit {
       listHeading: string = 'Some Coding Skills I Know';
       skills: string[] = ['Loops', 'Conditionals', 'Functions', 'Classes', 'Modules', 'Git', 'HTML/CSS'];
       alternateColor: string = 'black';
       bulletType: string = 'A';
       changeColor: boolean = true;
    
       constructor() { }
    
       ngOnInit() { }
    
    }
    
  4. NEAT! Reassigning the alternateColor variable in the .ts file causes EVERY tag with [style.color]="alternateColor" to change color.

Try It

Change the values for the alternateColor and bulletType variables. Save your work and refresh the web page to see the results.

Note that bulletType takes options of numbers (1), upper and lower case letters (A, a), or upper and lower case Roman numerals (I, i). For a detailed description of using the type attribute in an ordered list, check out the W3 schools documentation.

30.3.2.2. Changing Styles with Booleans

We can accomplish the same results by applying a class to the second ol tag:

  1. Add the following code to skill-set.component.css:

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    .ol-style {
       color: black;
       text-align: center;
       list-style-type: upper-roman;
    }
    

    Note

    The CSS property list-style-type defines the look of the list item markers, similar to the ol element's type attribute. The values available to the CSS property are different, however. You can find a full list at W3 schools.

  2. Next, modify line 8 in the starter HTML:

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    <div class="skills">
       <h3>{{listHeading}}</h3>
       <ol [style.color]="alternateColor" [type]="bulletType">
          <li *ngFor="let skill of skills">{{skill}}</li>
       </ol>
       <hr>
       <h3>Copy of Skill List</h3>
       <ol [class.ol-style]="changeColor">
          <li *ngFor="let skill of skills">{{skill}}</li>
       </ol>
       <hr>
       <p>Here is some practice text...</p>
    </div>
    

    After saving these updates, the skills list changes appearance:

    Attribute directives midpoint screen.
  3. Instead of setting [class.ol-style] equal to a string, the changeColor variable is a boolean defined in the skill-set.component.ts file. If changeColor is true, Angular adds the ol-style class of the tag. If changeColor is false, the class remains absent from the tag.

Try It

  1. Set changeColor to false and verify that the second ordered list changes back to green, left-aligned, and numbered.
  2. Create a p-style class in the CSS file and modify line 12 in skill-set.component.html to make the color and alignment of the p element depend on !changeColor.

30.3.3. What About the Buttons?

Nice display of eagerness! We will deal with the buttons on the next page.

30.3.4. Check Your Understanding

The reversed attribute labels ordered lists from highest to lowest values (9, 8, 7... instead of 1, 2, 3...). Unlike the class or style attributes, reversed is not set equal to a string inside the HTML tag. Just having it in the tag flips the numbering of the bullets.

<ol style="color: blue" reversed>

Question

How could we data-bind the reversed attribute in an ol tag? Indicate ALL working options.

  1. Bind the attribute to a variable that holds the string "reversed" or "notReversed".
  2. Bind the attribute to a boolean variable set as true or false.
  3. Bind the attribute to a boolean statement like variable1 > variable2.
  4. Bind the attribute to the empty string "".
  5. Just put square brackets around reversed and hope for the best.