How to implement pull-up to change nav color function in uniapp

With the popularity of mobile applications, uniapp is very popular as a cross-platform application development framework. The pull-up function to change the nav color makes many developers put it down. Next, let’s explore how to implement this function.

1. Determine the requirements: When the page is pulled down to a certain height, the background color of the navigation (nav) at the top of the page changes.

2. Modify the HTML file: add a fixed-position navigation bar at the top of the page, and set its background color to the color that needs to be changed.

3. Modify the JS file: Obtain the scroll height of the page by listening to the page pull-down event. When the scroll height reaches a certain value, modify the background color of the navigation bar.

Now, let’s take a detailed look at the specific implementation process.

1. Determine the needs

Before we start to implement the function of pulling up to change the color of the navigation bar, we need to first determine our own needs. For example, we have a page that needs to change the background color of the navigation bar to red when the drop-down height is 400px. Then, we need to add a navigation bar to the HTML file and set its background color to red.

<template>
  <view>
    <!-- 导航栏 -->
    <view></view>
    <!-- 页面主体 -->
    <view>
      <!-- 页面内容 -->
    </view>
  </view>
</template>

2. Modify the JS file

Next, we need to implement in the JS file the function of changing the color of the navigation bar when the page is pulled down to a certain height. Here, we can use onPageScroll provided by uniapp to listen for page sliding events.

onLoad() {
  // 监听页面滚动事件
  uni.pageScrollTo({
    scrollTop: 0, // 滚动到页面顶部
    duration: 0 // 滚动时间为0毫秒
  })
  uni
    .createIntersectionObserver(this, { observeAll: true })
    .relativeToViewport({ bottom: 0 }, ({ intersectionRect }) => {
      // 当页面滚动高度达到400px时，改变导航栏背景色
      if (intersectionRect.top 
The implementation logic of this code is that when the scroll height reaches 400px, call uni.setBackgroundColor to change the background color of the navigation bar to red. 
It should be noted here that if you want to modify the webview background color in the uni.setBackgroundColor method, you must pass in the webviewId of the current page. We can get all currently open webview instances through uni.getCurrentPages(), and then get the webviewId of the last page. It is recommended here to obtain the webviewId according to the writing method in the uniapp instance, which can avoid some problems in subsequent development. 
3. Complete code
Finally, the function of pulling up to change the color of the navigation bar is implemented as follows: 
<template>
  <view>
    <!-- 导航栏 -->
    <view></view>
    <!-- 页面主体 -->
    <view>
      <!-- 页面内容 -->
    </view>
  </view>
</template>

<script>
  export default {
    data() {
      return {
        style: &#39;&#39;
      }
    },
    onLoad() {
      // 监听页面滚动事件
      uni.pageScrollTo({
        scrollTop: 0, // 滚动到页面顶部
        duration: 0 // 滚动时间为0毫秒
      })
      uni
        .createIntersectionObserver(this, { observeAll: true })
        .relativeToViewport({ bottom: 0 }, ({ intersectionRect }) => {
          // 当页面滚动高度达到400px时，改变导航栏背景色
          if (intersectionRect.top <= 400) {
            this.style = &#39;background-color: #ff0000;&#39;
            uni.setBackgroundColor({
              backgroundColor: &#39;#ff0000&#39;,
              // 只是横向背景色改变时可不传此参数
              // 必须要传递的参数是调用这个API的webviewId，可以通过payload或getCurrentPages()获取当前webview对象，再从webview对象中获取id
              // 在getCurrentPages()会得到已经打开过的页面的web-view实例对象
              webviewId: getCurrentPages()[getCurrentPages().length - 1].$getOpenerEventChannel().id
            })
          } else {
            this.style = &#39;background-color: #ffffff;&#39;
            uni.setBackgroundColor({
              backgroundColor: &#39;#ffffff&#39;,
              webviewId: getCurrentPages()[getCurrentPages().length - 1].$getOpenerEventChannel().id
            })
          }
        })
    }
  }
</script>

In summary, through the above three steps, we You can implement the pull-up function to change the color of the navigation bar in uniapp. Hope this article helps you! 

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