fixed 19a9c340 from https://gitee.com/zhuzijia/docs/pulls/20155

修改狀態管理文檔約束
Signed-off-by: Nzhuzijia <zhuzijia@huawei.com>
Change-Id: I16d7b3d55396222b38bf498297e269f095ead2f5

zh-cn/application-dev/quick-start/arkts-appstorage.md

@@ -193,6 +193,181 @@ struct CompA {
 }
 ```
 
+### 以持久化方式订阅某个事件并接收事件回调
+
+推荐使用持久化方式订阅某个事件并接收事件回调，可以减少开销，增强代码的可读性。
+
+
+```ts
+// xxx.ets
+import emitter from '@ohos.events.emitter';
+
+let NextID: number = 0;
+
+class ViewData {
+  title: string;
+  uri: Resource;
+  color: Color = Color.Black;
+  id: number;
+
+  constructor(title: string, uri: Resource) {
+    this.title = title;
+    this.uri = uri
+    this.id = NextID++;
+  }
+}
+
+@Entry
+@Component
+struct Gallery2 {
+  dataList: Array<ViewData> = [new ViewData('flower', $r('app.media.icon')), new ViewData('OMG', $r('app.media.icon')), new ViewData('OMG', $r('app.media.icon'))]
+  scroller: Scroller = new Scroller()
+  private preIndex: number = -1
+
+  build() {
+    Column() {
+      Grid(this.scroller) {
+        ForEach(this.dataList, (item: ViewData) => {
+          GridItem() {
+            TapImage({
+              uri: item.uri,
+              index: item.id
+            })
+          }.aspectRatio(1)
+          .onClick(() => {
+            if (this.preIndex === item.id) {
+              return
+            }
+            var innerEvent = { eventId: item.id }
+            // 选中态：黑变红
+            var eventData = {
+              data: {
+                "colorTag": 1
+              }
+            }
+            emitter.emit(innerEvent, eventData)
+
+            if (this.preIndex != -1) {
+              console.info(`preIndex: ${this.preIndex}, index: ${item.id}, black`)
+              var innerEvent = { eventId: this.preIndex }
+              // 取消选中态：红变黑
+              var eventData = {
+                data: {
+                  "colorTag": 0
+                }
+              }
+              emitter.emit(innerEvent, eventData)
+            }
+            this.preIndex = item.id
+          })
+
+        }, (item: ViewData) => JSON.stringify(item))
+      }.columnsTemplate('1fr 1fr')
+    }
+
+  }
+}
+
+@Component
+export struct TapImage {
+  @State tapColor: Color = Color.Black;
+  private index: number;
+  private uri: Resource;
+
+  onTapIndexChange(colorTag: emitter.EventData) {
+    this.tapColor = colorTag.data.colorTag ? Color.Red : Color.Black
+  }
+
+  aboutToAppear() {
+    //定义事件ID
+    var innerEvent = { eventId: this.index }
+    emitter.on(innerEvent, this.onTapIndexChange.bind(this))
+  }
+
+  build() {
+    Column() {
+      Image(this.uri)
+        .objectFit(ImageFit.Cover)
+        .border({ width: 5, style: BorderStyle.Dotted, color: this.tapColor })
+    }
+  }
+}
+```
+
+以下示例为消息机制方式订阅事件，会导致回调监听的节点数较多，非常耗时，不推荐以此来实现应用代码。
+
+
+```ts
+// xxx.ets
+class ViewData {
+  title: string;
+  uri: Resource;
+  color: Color = Color.Black;
+
+  constructor(title: string, uri: Resource) {
+    this.title = title;
+    this.uri = uri
+  }
+}
+
+@Entry
+@Component
+struct Gallery2 {
+  dataList: Array<ViewData> = [new ViewData('flower', $r('app.media.icon')), new ViewData('OMG', $r('app.media.icon')), new ViewData('OMG', $r('app.media.icon'))]
+  scroller: Scroller = new Scroller()
+
+  build() {
+    Column() {
+      Grid(this.scroller) {
+        ForEach(this.dataList, (item: ViewData, index?: number) => {
+          GridItem() {
+            TapImage({
+              uri: item.uri,
+              index: index
+            })
+          }.aspectRatio(1)
+
+        }, (item: ViewData, index?: number) => {
+          return JSON.stringify(item) + index;
+        })
+      }.columnsTemplate('1fr 1fr')
+    }
+
+  }
+}
+
+@Component
+export struct TapImage {
+  @StorageLink('tapIndex') @Watch('onTapIndexChange') tapIndex: number = -1;
+  @State tapColor: Color = Color.Black;
+  private index: number;
+  private uri: Resource;
+
+  // 判断是否被选中
+  onTapIndexChange() {
+    if (this.tapIndex >= 0 && this.index === this.tapIndex) {
+      console.info(`tapindex: ${this.tapIndex}, index: ${this.index}, red`)
+      this.tapColor = Color.Red;
+    } else {
+      console.info(`tapindex: ${this.tapIndex}, index: ${this.index}, black`)
+      this.tapColor = Color.Black;
+    }
+  }
+
+  build() {
+    Column() {
+      Image(this.uri)
+        .objectFit(ImageFit.Cover)
+        .onClick(() => {
+          this.tapIndex = this.index;
+        })
+        .border({ width: 5, style: BorderStyle.Dotted, color: this.tapColor })
+    }
+
+  }
+}
+```
+
 
 ## 限制条件
 
@@ -201,4 +376,6 @@ AppStorage与[PersistentStorage](arkts-persiststorage.md)以及[Environment](ark
 - 在AppStorage中创建属性后，调用PersistentStorage.PersistProp()接口时，会使用在AppStorage中已经存在的值，并覆盖PersistentStorage中的同名属性，所以建议要使用相反的调用顺序，反例可见[在PersistentStorage之前访问AppStorage中的属性](arkts-persiststorage.md#在persistentstorage之前访问appstorage中的属性)；
 
 - 如果在AppStorage中已经创建属性后，再调用Environment.EnvProp()创建同名的属性，会调用失败。因为AppStorage已经有同名属性，Environment环境变量不会再写入AppStorage中，所以建议AppStorage中属性不要使用Environment预置环境变量名。
+
+- 状态装饰器装饰的变量，改变会引起UI的渲染更新，如果改变的变量不是用于UI更新，只是用于消息传递，推荐使用 emitter方式。例子可见[以持久化方式订阅某个事件并接收事件回调](#以持久化方式订阅某个事件并接收事件回调)。
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