直接上代码

<template>
    <view class="holdon" >
        <image  class="ball" :style="'left:'+moveX+'px;top:'+moveY+'px'"     
                @touchstart="drag_start" @touchmove.prevent="drag_hmove"  mode="aspectFit">
        </image>
    </view>
</template>
<script>
    export default {
        data() {
            return {
                start:[0,0],
                moveY:0,
                moveX:0,
                windowWidth:'',
                windowHeight:'',
            }
        },
        onShow() {
            const { windowWidth, windowHeight } = uni.getSystemInfoSync();  
            this.windowWidth = windowWidth
            this.windowHeight = windowHeight
        },
        methods: {
            drag_start(event){
                this.start[0]= event.touches[0].clientX-event.target.offsetLeft;
                this.start[1]= event.touches[0].clientY-event.target.offsetTop;
            },
            drag_hmove(event){
                    let  tag     = event.touches;
                    if(tag[0].clientX < 0 ){
                        tag[0].clientX = 0
                    }
                    if(tag[0].clientY < 0 ){
                        tag[0].clientY = 0
                    }
                    if(tag[0].clientX > this.windowWidth ){
                        tag[0].clientX = this.windowWidth
                    }
                    if(tag[0].clientY > this.windowHeight ){
                        tag[0].clientY = this.windowHeight
                    }
                    this.moveX   = tag[0].clientX-this.start[0];
                    this.moveY   = tag[0].clientY-this.start[1];
            }
        }}
</script>
 
<style>
    .holdon{
        width: 100%;
        height: 100%;
    }
    .ball{
        width: 70upx;height: 70upx;
        background:linear-gradient(to bottom, #F8F8FF,#87CEFA);
        border-radius: 50%;
        box-shadow: 0 0 15upx #87CEFA;
        color: #fff;
        font-size: 30upx;
        display: flex;justify-content: center;align-items: center;
        position: fixed !important;
        z-index: 1000000;
    }
</style>