Map对象使用[]赋值，Map中的size不递增

@Entry
@Component
struct MapPage {
@State map: Map<string, string> = new Map<string, string>()

build() {
Button('点击')
.onClick(() => {
this.map.set('a1', 'a1');
console.log(this.map.size.toString())
})
}
}
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