修改pdf错误提示

src/components/course/course-ware.vue

 <template>
   <div class="course-ware">
-    <div v-show="url" class="canvas-box"></div>
+    <div v-show="url && loadPdf" class="canvas-box"></div>
     <p v-show="!url" class="tip">无相关课件</p>
   </div>
 </template>
@@ -26,6 +26,11 @@ export default {
       default: true,
     }
   },
+  data() {
+    return {
+      loadPdf: false
+    }
+  },
   watch: {
     url(val) {
       this.drawPDF();
@@ -56,6 +61,7 @@ export default {
         for (let item of pages) {
           this.createCanvas(item)
         }
+        this.loadPdf = true;
       } catch(err) {
         console.log(err)
       }