API Komposisi Vue 3 - Objek yang berpotensi kosong

Question

Saya menggunakan api Vue 3 Composition dan Typescript untuk melaksanakan pinch untuk zum menggunakan pakej HammerJS.

Saya cuba mengikuti contoh kerja CodePen yang ditulis dalam JavaScript: https://codepen.io/bakho/details/GBzvbB dilaksanakan dalam Vue.

Walau bagaimanapun, saya menghadapi beberapa isu semasa cuba menjalankannya dalam apl Vue saya dan saya tidak pasti cara untuk membetulkannya.

Ralat berikut:

// Object is possibly 'null'.
imageContainer.value.offsetWidth;

// Object is possibly 'null'.
imageContainer.value.appendChild(displayImage);

// Object is possibly 'null'.
imageContainer.value.addEventList ener...

Ini adalah kod sumber lengkap:

<template>
  <h1>Image Zoom</h1>
  <div class="imageContainer" ref="imageContainer"></div>
</template>

<script lang="ts">
import Hammer from "hammerjs";
import { defineComponent } from "vue";
import { ref } from 'vue';

export default defineComponent({
  setup() {
    const imageUrl = "https://source.unsplash.com/random";
    const imageContainer = ref(null)

    let minScale = 1; let maxScale = 4; let imageWidth : any; let imageHeight : any; let containerWidth : any;
    let containerHeight : any; let displayImageX = 0; let displayImageY = 0; let displayImageScale = 1;
    let displayDefaultWidth : any; let displayDefaultHeight 
    let rangeX = 0; let rangeMaxX = 0; let rangeMinX = 0;
    let rangeY = 0; let rangeMaxY = 0; let rangeMinY = 0;

    // let displayImageRangeY = 0;

    let displayImageCurrentX = 0;
    let displayImageCurrentY = 0;
    let displayImageCurrentScale = 1;

    function resizeContainer() {
      containerWidth = imageContainer.value.offsetWidth;
      containerHeight = imageContainer.value.offsetHeight;
      if (displayDefaultWidth !== undefined && displayDefaultHeight !== undefined) {
        displayDefaultWidth = displayImage.offsetWidth;
        displayDefaultHeight = displayImage.offsetHeight;
        updateRange();
        displayImageCurrentX = clamp(displayImageX, rangeMinX, rangeMaxX);
        displayImageCurrentY = clamp(displayImageY, rangeMinY, rangeMaxY);
        updateDisplayImage(
          displayImageCurrentX,
          displayImageCurrentY,
          displayImageCurrentScale
        );
      }
    }
    resizeContainer();

    function clamp(value, min, max) {
      return Math.min(Math.max(min, value), max);
    }

    function clampScale(newScale) {
      return clamp(newScale, minScale, maxScale);
    }

    const displayImage = new Image();
        displayImage.src = imageUrl;
        displayImage.onload = function(){
        imageWidth = displayImage.width;
        imageHeight = displayImage.height;
        imageContainer.value.appendChild(displayImage);
        displayImage.addEventListe ner('mousedown', e => e.preventDefault(), false);
        displayDefaultWidth = displayImage.offsetWidth;
        displayDefaultHeight = displayImage.offsetHeight;
        rangeX = Math.max(0, displayDefaultWidth - containerWidth);
        rangeY = Math.max(0, displayDefaultHeight - containerHeight);
    }

    imageContainer.value.addEventLis tener('wheel', e => {
        displayImageScale = displayImageCurrentScale = clampScale(displayImageScale + (e.wheelDelta / 800));
        updateRange();
        displayImageCurrentX = clamp(displayImageCurrentX, rangeMinX, rangeMaxX)
        displayImageCurrentY = clamp(displayImageCurrentY, rangeMinY, rangeMaxY)
        updateDisplayImage(displayImageCurrentX, displayImageCurrentY, displayImageScale);  
    }, false);

    function updateDisplayImage(x, y, scale) {
        const transform = 'translateX(' + x + 'px) translateY(' + y + 'px) translateZ(0px) scale(' + scale + ',' + scale + ')';
        displayImage.style.transform = transform;
        displayImage.style.webkitTransform = transform;
        displayImage.style.transform = transform;
    }

    function updateRange() {
        rangeX = Math.max(0, Math.round(displayDefaultWidth * displayImageCurrentScale) - containerWidth);
        rangeY = Math.max(0, Math.round(displayDefaultHeight * displayImageCurrentScale) - containerHeight);
        
        rangeMaxX = Math.round(rangeX / 2);
        rangeMinX = 0 - rangeMaxX;

        rangeMaxY = Math.round(rangeY / 2);
        rangeMinY = 0 - rangeMaxY;
    }

    const hammertime = new Hammer(imageContainer);
    hammertime.get('pinch').set({ enable: true });
    hammertime.get('pan').set({ direction: Hammer.DIRECTION_ALL });

    hammertime.on('pan', ev => {  
        displayImageCurrentX = clamp(displayImageX + ev.deltaX, rangeMinX, rangeMaxX);
        displayImageCurrentY = clamp(displayImageY + ev.deltaY, rangeMinY, rangeMaxY);
        updateDisplayImage(displayImageCurrentX, displayImageCurrentY, displayImageScale);
    });

    hammertime.on('pinch pinchmove', ev => {
        displayImageCurrentScale = clampScale(ev.scale * displayImageScale);
        updateRange();
        displayImageCurrentX = clamp(displayImageX + ev.deltaX, rangeMinX, rangeMaxX);
        displayImageCurrentY = clamp(displayImageY + ev.deltaY, rangeMinY, rangeMaxY);
        updateDisplayImage(displayImageCurrentX, displayImageCurrentY, displayImageCurrentScale);
    });

    hammertime.on('panend pancancel pinchend pinchcancel', () => {
        displayImageScale = displayImageCurrentScale;
        displayImageX = displayImageCurrentX;
        displayImageY = displayImageCurrentY;
    }); 

    return {};
  },
});
</script>

<style>
.imageContainer {
  width: 96%;
  height: 96%;
  max-width: 800px;
  max-height: 600px;
  position: absolute;
  overflow: hidden;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  margin: auto;
  background: #2b2b2c;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
}
.imageContainer > img {
  display: block;
  max-width: 100%;
  max-height: 100%;
  cursor: move;
  touch-action: none;
}
</style>

Boleh sesiapa beritahu saya apa yang salah dan mengapa ia menyebabkan ini Object 可能为“null”

Answer 1

Ini adalah sebab kesilapan:

• const imageContainer = ref(null) -> 您将值设置为 null 并且 TypeScript 警告您对该对象的属性的任何访问都可能引发错误，因为初始值为 null 并且因为您尝试在模板中使用 ref Elemen ini mungkin wujud atau tidak.

• const imageContainer = document.querySelector('.imageContainer') -> 您正在查询存在或不存在的 HTML 元素，这意味着您还可以获取 null sebagai nilai, dan TypeScript sekali lagi memberi amaran kepada anda bahawa sebarang akses kepada sifat objek mungkin menimbulkan ralat

Penyelesaian:

• Anda mesti membuat panggilan daripada setup 函数返回 setup 变量，以便 Vue 将其与模板中的 ref 绑定，并且可以在 onMounted 函数内部访问该变量，因为它是 ref ，这意味着它尚未安装到 DOM 中。 setup 在 Vue.js 组件生命周期中的 created 和 mounted sebelum cangkuk, dan anda tidak mempunyai akses kepada mana-mana kandungan DOM di dalamnya.

import { ref, onMounted } from 'vue'

export default {
  setup() {
    const imageContainer = ref(null)

    onMounted(() => {
      // here you access imageContainer variable
    })

    return {
      imageContainer 
    }
  }
}