优化翻页效果(同步更新)

src/components/DashBoard.vue

@@ -124,6 +124,7 @@
       在线预览<hr>
       <span style="display: inline-block">在线预览分页页数:</span>
       <input v-model="lengthPerPage">
+      (建议为3的倍数，因为固定了一行三张)
     </div>
     <template #footer>
       <el-button type="primary" @click="saveConfig">保存</el-button>
@@ -538,8 +539,14 @@ function saveConfig(){
     }
   }
 
-  store.state.lengthPerPage = Number(lengthPerPage.value)
-  localStorage.setItem("lengthPerPage", lengthPerPage.value)
+  if(lengthPerPage.value < 0 || lengthPerPage.value > 30) {
+    ElMessage("分页页数设置错误，范围1~30")
+    lengthPerPage.value = 30
+  }
+  else {
+    store.state.lengthPerPage = Number(lengthPerPage.value)
+    localStorage.setItem("lengthPerPage", lengthPerPage.value)
+  }
   localStorage.setItem("darkConfig", JSON.stringify(darkConfig.value))
   isConfig.value = false
   adjustForStyle()