Detailed explanation of the principle and application scenarios of keep-alive in Vue

Detailed explanation of the principle and application scenarios of keep-alive in vue

In Vue, we often encounter situations where we need to retain the state of components when switching between components. At this time, the keep-alive component in Vue can play an important role. This article will explain the principle of keep-alive in detail and introduce its application scenarios.

1. The principle of keep-alive
keep-alive is an abstract component provided by Vue. It can cache the components it wraps and retain the state, thus avoiding the need to recreate them every time the component is switched. and destruction overhead. Specifically, keep-alive will create a cache object named cache to store cached component instances.

When a component wrapped by keep-alive is switched out, its instance will be cached in the cache. When switching back, if the previously cached component instance exists, the instance will be taken directly from the cache and remounted to the DOM. In this way, the state of the component can be retained, and life cycle hook functions such as created and mounted will not be re-executed.

2. Keep-alive application scenarios

1. Forward and backward page caching
   In some application scenarios, we hope that when the user forwards or backwards the page, the page can remain original. state without the need to reload data. At this time, you can use keep-alive to cache page components. When the user returns to the previous page, the page will retrieve the instance directly from the cache and display the previous state.
2. tab switching cache
   In some pages, we may use tabs to switch different content. If the content is reloaded every time you switch, it will lead to a poor user experience. At this time, you can wrap the content components corresponding to each tab with keep-alive to achieve the effect of retaining state between different tabs.
3. Route switching cache
   When we use vue-router to switch routes, sometimes we also need to maintain the state of the component. For example, in the product details page of an e-commerce website, after the user enters the details page from the home page and clicks the return button to return to the home page, he or she hopes to be able to return to the original scrolling position instead of starting from the beginning. At this time, you can use keep-alive to wrap the product details page component to maintain the scroll position.

The following is an example of using keep-alive:

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<keep-alive>
  <router-view></router-view>
</keep-alive>

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In the above example, we use keep-alive to wrap the router-view, thus retaining the state of the routing component. When switching routes, the previous route components are cached and reused when needed.

In addition to using keep-alive in templates, we can also dynamically control caching in the program. By setting the include and exclude properties, we can specify which components need to be cached and which components need to be excluded from the cache.

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In the above example, we only wrap ComponentA in keep-alive and exclude ComponentB, so that only the ComponentA component is cached.

Summary:
keep-alive is a very useful component provided by Vue. It can help us cache component instances and thereby retain the state of the component. Keep-alive can be used to improve user experience in scenarios such as forward and backward pages, tab switching, route switching, etc. It should be noted that when using keep-alive, you need to pay attention to the activated and deactivated hook functions of the component.

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