The control box to show hidden layer and change the internal image src, first displayed on a map will then switch

<div class="cart" v-show="cart">
    <div class="cart-content">
        <img :src="imgUrl" />
    </div>
</div>

// display contents and switching cards 
showCart (I) { 
　　 // not solve the problem 
　　 //this.imgUrl = '';
     the this .imgUrl = the this .url [I];
     the this .cart = to true ; 
}, 
// hide card 
closeCard () { 
    the this .cart = to false ; 
},

These are the problems in your code

1. Use the v-if, without v-show, brings frequent switching consumption

2. After you hide empty card imgUrl

closeCard(){
　　this.card = false;
　　this.imgUrl = '';        
}

3. Use multiple cards (recommended)