style：设备运行参数分析-图表效果优化

src/views/iot/deviceParamAnalysis/index.vue

@@ -59,7 +59,13 @@
         />
         <div v-loading="chartLoading">
           <el-empty v-if="!selectedParam" description="请选择左侧参数" />
-          <EChart v-else :key="chartRenderKey" :options="chartOption" height="70vh" />
+          <el-empty v-else-if="chartState === 'empty'" description="暂无数据" />
+          <EChart
+            v-else-if="chartState === 'ready'"
+            :key="chartRenderKey"
+            :options="chartOption"
+            height="70vh"
+          />
         </div>
       </ContentWrap>
     </el-col>
@@ -120,6 +126,7 @@ const selectedModelId = ref<number | undefined>(undefined)
 
 const selectedParam = ref<DeviceTreeNode | null>(null)
 const chartLoading = ref(false)
+const chartState = ref<'idle' | 'loading' | 'empty' | 'ready'>('idle')
 const chartXAxis = ref<string[]>([])
 const chartSeries = ref<{ name: string; data: Array<number | null> }[]>([])
 const chartRenderKey = ref(0)
@@ -251,6 +258,7 @@ const loadTree = async () => {
       selectedParam.value = null
       selectedDeviceId.value = undefined
       selectedModelId.value = undefined
+      chartState.value = 'idle'
       chartXAxis.value = []
       chartSeries.value = []
     }
@@ -300,6 +308,7 @@ const fetchChart = async () => {
     return date.includes(':') ? date : `${date} ${suffix}`
   }
 
+  chartState.value = 'loading'
   chartLoading.value = true
   resetChartData()
   try {
@@ -313,6 +322,7 @@ const fetchChart = async () => {
     if (!rows.length) {
       chartXAxis.value = []
       chartSeries.value = []
+      chartState.value = 'empty'
       return
     }
 
@@ -356,8 +366,11 @@ const fetchChart = async () => {
       const values = keys.map((k) => toNumber(firstRow[k]))
       chartSeries.value = [{ name: param?.label || '参数', data: values }]
     }
+
+    chartState.value = chartXAxis.value.length && chartSeries.value.length ? 'ready' : 'empty'
   } catch {
     message.error('获取图表数据失败')
+    chartState.value = 'idle'
   } finally {
     chartLoading.value = false
   }