AngularJS - 切換選單

Hello, aspiring programmers! Today, we're going to dive into the world of AngularJS and explore a nifty little feature called the Switch Menu. Don't worry if you're new to programming – I'll guide you through this step by step, just like I've done for countless students over my years of teaching. So, grab a cup of coffee (or your favorite beverage), and let's get started!

What is a Switch Menu?

Before we jump into the code, let's understand what a Switch Menu is. Imagine you're in a restaurant, and the waiter hands you a menu. But this isn't just any menu – it's a magical menu that changes based on what you're in the mood for. That's essentially what a Switch Menu does in AngularJS!

A Switch Menu allows us to display different content based on a specific condition or value. It's like having multiple light switches, where flipping one switch turns on a specific light. In our case, we're switching between different pieces of content.

Basic Structure of a Switch Menu

Let's start with the basic structure of a Switch Menu in AngularJS. Here's a simple example:

<div ng-switch on="expression">
<div ng-switch-when="value1">Content for value1</div>
<div ng-switch-when="value2">Content for value2</div>
<div ng-switch-default>Default content</div>
</div>

Let's break this down:

1. ng-switch: This is the main directive that creates our switch menu.
2. on="expression": This is where we specify what we're switching on. It could be a variable, a function, or any valid AngularJS expression.
3. ng-switch-when: This directive specifies a case for our switch. If the expression matches this value, the content inside will be displayed.
4. ng-switch-default: This is our fallback content. If none of the ng-switch-when cases match, this content will be shown.

A Real-World Example

Now, let's create a more practical example. Imagine we're building a simple weather app that shows different messages based on the temperature. Here's how we could implement that:

<div ng-controller="WeatherController">
<h2>Today's Weather</h2>
<p>Temperature: {{temperature}}°C</p>
<div ng-switch on="temperature">
<div ng-switch-when="30">It's scorching hot! Stay hydrated!</div>
<div ng-switch-when="20">Perfect weather for a picnic!</div>
<div ng-switch-when="10">Better grab a jacket!</div>
<div ng-switch-default>No specific advice for this temperature.</div>
</div>
</div>

app.controller('WeatherController', function($scope) {
$scope.temperature = 20; // This could be dynamically updated
});

In this example, we're switching based on the temperature value. Depending on the temperature, a different message will be displayed to the user.

Using Ranges in Switch Menu

But wait, you might be thinking, "What if I want to show a message for a range of temperatures?" Great question! We can use expressions in our ng-switch-when to achieve this. Let's modify our example:

<div ng-controller="WeatherController">
<h2>Today's Weather</h2>
<p>Temperature: {{temperature}}°C</p>
<div ng-switch on="true">
<div ng-switch-when="temperature >= 30">It's scorching hot! Stay hydrated!</div>
<div ng-switch-when="temperature >= 20 && temperature < 30">Perfect weather for a picnic!</div>
<div ng-switch-when="temperature >= 10 && temperature < 20">Better grab a jacket!</div>
<div ng-switch-default>Brrr! It's cold out there!</div>
</div>
</div>

Now we're using on="true" and putting our conditions in the ng-switch-when attributes. This gives us more flexibility in defining our cases.

Switch Menu with Multiple Values

Sometimes, you might want to display the same content for multiple values. AngularJS has got you covered! You can use an array of values in your ng-switch-when. Here's an example:

<div ng-controller="DayController">
<h2>Today is: {{day}}</h2>
<div ng-switch on="day">
<div ng-switch-when="['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']">It's a weekday. Time to work!</div>
<div ng-switch-when="['Saturday', 'Sunday']">It's the weekend. Time to relax!</div>
<div ng-switch-default>Invalid day</div>
</div>
</div>

app.controller('DayController', function($scope) {
var days = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];
$scope.day = days[new Date().getDay()];
});

This example will display different messages depending on whether it's a weekday or weekend.

Best Practices for Using Switch Menu

As with any programming technique, there are some best practices to keep in mind when using Switch Menus:

1. Keep it simple: If you find yourself with too many cases, consider if there's a more efficient way to structure your code.
2. Use meaningful expressions: Make sure your switch expression is clear and understandable.
3. Don't forget the default case: Always include a default case to handle unexpected values.
4. Consider performance: For very large switch statements, consider if a different approach might be more efficient.

Conclusion

And there you have it, folks! We've switched our way through the basics of AngularJS Switch Menus. From simple switches to more complex examples with ranges and multiple values, you now have the power to create dynamic, condition-based content in your AngularJS applications.

Remember, like learning to ride a bike, mastering AngularJS takes practice. Don't be discouraged if it doesn't click immediately – keep experimenting, keep coding, and before you know it, you'll be switching like a pro!

Happy coding, and may your switches always be in the right position!

Method	Description
ng-switch	The main directive that creates the switch menu
on	Specifies the expression to switch on
ng-switch-when	Defines a case for the switch
ng-switch-default	Defines the default case

Credits: Image by storyset