Vue and Element-UI Cascading Pull-down Box Case Tutorial

The cascading selectors in Vue and Element-UI handle not only parent-child relationships, but a tree-shaped data structure. Through careful data design, complex scenarios such as multi-level linkage between provinces, cities and counties can be achieved. Pay attention to performance optimization when loading asynchronously, such as using virtual scrolling, caching and anti-shake/throttling technologies. For code quality, readability, maintainability and performance should be emphasized.

Vue and Element-UI cascade selectors: more than just a simple parent-son relationship

Have you ever wondered how to elegantly implement a cascading drop-down box in a Vue project to make the user experience smoother and the code simpler? This article takes you into the cascading selectors of Vue and Element-UI, which not only teaches you how to use them, but more importantly, understand the mechanisms behind them and how to avoid some common pitfalls. After reading, you will be able to independently complete various complex cascading selection scenarios and write efficient and maintainable code.

Let’s start with the basics. Element-UI's el-cascader component looks like a multi-stage linkage selector on the surface, but in fact, behind it is a clever combination of data structures and event processing. You have to understand that it does not handle simple parent-son relationships, but a tree-shaped data. Each node of this tree represents an option, and the parent and child nodes are connected through children attribute. This is not a simple array set, but requires careful design of data structures to exert the power of el-cascader .

Let’s take a simple example, suppose we want to conduct a three-level linkage between provinces, cities and counties:

 <code class="javascript"><template> <el-cascader v-model="selectedOptions" :options="options" :props="{ label: 'label', value: 'value', children: 'children' }"></el-cascader> <p>Selected: {{ selectedOptions }}</p> </template> <script> export default { data() { return { selectedOptions: [], options: [ { value: &#39;北京&#39;, label: &#39;北京&#39;, children: [ { value: &#39;朝阳&#39;, label: &#39;朝阳&#39; }, { value: &#39;海淀&#39;, label: &#39;海淀&#39; } ] }, { value: &#39;上海&#39;, label: &#39;上海&#39;, children: [ { value: &#39;浦东&#39;, label: &#39;浦东&#39; }, { value: &#39;黄浦&#39;, label: &#39;黄浦&#39; } ] } ] }; }, methods: { handleChange(value) { console.log(value); // 处理选择的省市县} } }; </script></code>

This code shows the most basic usage. options attribute defines the data structure, props attribute specifies the names of label , value and children fields, v-model binds the selected value, and @change event listens for the selection change. Note that value field is what you use to uniquely identify each option, and it will be returned in the handleChange function.

But this is just the tip of the iceberg. In actual applications, your data may come from the backend interface and need to be loaded asynchronously. At this time, you need to use a function in the options property, which returns a Promise. After the Promise is resolved, el-cascader will re-render. Remember that performance and user experience are crucial when loading asynchronously, avoiding unnecessary requests and redundant data.

Going deeper, you may encounter situations where you need to dynamically load children based on the selected parent node. This requires you to cleverly combine @change events and asynchronous requests. Each time a change is selected, a new request is triggered to obtain the data of the corresponding child nodes. This part of the code will be more complicated and requires careful processing of the loading state to avoid users from seeing flickering or error prompts. A good practice is to use a loading status indicator to let users know that the data is loading.

Finally, some suggestions for performance optimization:

• Data structure optimization: If your data volume is large, consider using virtual scrolling or paging loading to avoid rendering all data at once.
• Cache: Caches loaded data to reduce duplicate requests.
• debounce/throttle: If your asynchronous requests are frequently triggered, use debounce or throttle technology to limit the frequency of requests.

Remember, the elegance of the code is not only reflected in the implementation of functions, but also in the readability, maintainability and performance. Don't sacrifice code quality in pursuit of fast implementation of features. A good cascading selector should be efficient, stable and easy to scale. Hopefully this article will help you better understand and use the cascading selectors of Vue and Element-UI and write better code.

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