{"id":4767,"date":"2021-12-25T21:27:35","date_gmt":"2021-12-25T13:27:35","guid":{"rendered":"http:\/\/123.57.164.21\/?p=4767"},"modified":"2021-12-25T21:27:35","modified_gmt":"2021-12-25T13:27:35","slug":"%e4%ba%86%e8%a7%a3-swiftui-%e7%9a%84-onchange","status":"publish","type":"post","link":"https:\/\/92it.top\/?p=4767","title":{"rendered":"\u4e86\u89e3 SwiftUI \u7684 onChange"},"content":{"rendered":"\n

\u8f6c\u8f7d\uff1ahttps:\/\/www.fatbobman.com\/posts\/onChange\/<\/p>\n\n\n\n

\u4ece iOS 14 \u5f00\u59cb\uff0cSwiftUI \u4e3a\u89c6\u56fe\u63d0\u4f9b\u4e86 onChange \u4fee\u9970\u5668\uff0c\u901a\u8fc7\u4f7f\u7528 onChange\uff0c\u6211\u4eec\u53ef\u4ee5\u5728\u89c6\u56fe\u4e2d\u5bf9\u7279\u5b9a\u7684\u503c\u8fdb\u884c\u89c2\u5bdf\uff0c\u5e76\u5728\u5176\u66f4\u6539\u65f6\u89e6\u53d1\u64cd\u4f5c\u3002\u672c\u6587\u5c06\u5bf9 onChange \u7684\u7279\u70b9\u3001\u7528\u6cd5\u3001\u6ce8\u610f\u4e8b\u9879\u4ee5\u53ca\u66ff\u4ee3\u65b9\u6848\u505a\u4ee5\u4ecb\u7ecd\u3002<\/p>\n\n\n\n

\u5982\u4f55\u4f7f\u7528 onChange<\/h5>\n\n\n\n
\n\n\n\n

onChange \u7684\u5b9a\u4e49\u5982\u4e0b\uff1a<\/p>\n\n\n\n

func onChange<V>(of value: V, perform action: @escaping (V) -> Void) -> some View where V : Equatable\n<\/pre>\n\n\n\n
onChange \u5728\u53d1\u73b0\u7279\u5b9a\u503c\u53d1\u751f\u53d8\u5316\u65f6\uff0c\u5c06\u8c03\u7528\u95ed\u5305\u4e2d\u7684\u64cd\u4f5c\u3002<\/p>\n\n\n\n
struct OnChangeDemo:View{\n    @State var t = 0\n    var body: some View{\n        Button(\"change\"){\n            t += 1\n        }\n        .onChange(of: t, perform: { value in\n            print(value)\n        })\n    }\n}\n<\/pre>\n\n\n\n
\u70b9\u51fb Button\uff0ct \u5c06\u52a0\u4e00\uff0conChange \u5c06\u5bf9 t \u503c\u8fdb\u884c\u6bd4\u8f83\uff0c\u5982\u679c\u503c\u53d1\u751f\u6539\u53d8\uff0c\u5c06\u8c03\u7528\u95ed\u5305\u6253\u5370\u65b0\u503c\u3002<\/p>\n\n\n\n
\u5728\u95ed\u5305\u4e2d\u53ef\u4ee5\u8fdb\u884c\u526f\u4f5c\u7528\u64cd\u4f5c\uff0c\u6216\u8005\u4fee\u6539\u89c6\u56fe\u4e2d\u7684\u5176\u4ed6\u53ef\u53d8\u5185\u5bb9\u3002<\/p>\n\n\n\n
\u4f20\u9012\u5230\u95ed\u5305\u4e2d\u7684\u503c\uff08\u4f8b\u5982\u4e0a\u9762\u7684 value\uff09\u662f\u4e0d\u53ef\u53d8\u7684\uff0c\u5982\u679c\u9700\u8981\u4fee\u6539\uff0c\u8bf7\u76f4\u63a5\u66f4\u6539\u89c6\u56fe\u4e2d\u7684\u53ef\u53d8\u503c\uff08t\uff09\u3002<\/p>\n\n\n\n
onChange \u7684\u95ed\u5305\u662f\u8fd0\u884c\u5728\u4e3b\u7ebf\u7a0b\u4e0a\u7684\uff0c\u5e94\u907f\u514d\u5728\u95ed\u5305\u4e2d\u6267\u884c\u8fd0\u884c\u65f6\u95f4\u957f\u7684\u4efb\u52a1\u3002<\/p>\n\n\n\n
\u5982\u4f55\u83b7\u53d6\u88ab\u89c2\u5bdf\u503c\u7684 OldValue<\/h5>\n\n\n\n
\n\n\n\n
onChange \u5141\u8bb8\u6211\u4eec\u901a\u8fc7\u95ed\u5305\u6355\u83b7\u7684\u65b9\u5f0f\u83b7\u53d6\u88ab\u89c2\u5bdf\u503c\u7684\u65e7\u503c\uff08oldValue\uff09\u3002\u4f8b\u5982\uff1a<\/p>\n\n\n\n
struct OldValue: View {\n    @State var t = 1\n    var body: some View {\n        Button(\"change\") {\n            t = Int.random(in: 1...5)\n        }\n        .onChange(of: t) { [t] newValue in\n            let oldValue = t\n            if newValue % oldValue == 2 {\n                print(\"\u4f59\u503c\u4e3a 2\")\n            } else {\n                print(\"\u4e0d\u6ee1\u8db3\u6761\u4ef6\")\n            }\n        }\n    }\n}\n<\/pre>\n\n\n\n
\u7531\u4e8e\u95ed\u5305\u4e2d\u6355\u83b7\u4e86 t\uff0c\u56e0\u6b64\u9700\u4f7f\u7528self.t<\/code>\u65b9\u80fd\u8c03\u7528\u89c6\u56fe\u4e2d\u7684 t\u3002<\/p>\n\n\n\n
\u5bf9\u4e8e\u7ed3\u6784\u7c7b\u578b\uff0c\u6355\u83b7\u65f6\u9700\u4f7f\u7528\u7ed3\u6784\u5b9e\u4f8b\uff0c\u800c\u4e0d\u80fd\u76f4\u63a5\u6355\u83b7\u7ed3\u6784\u4e2d\u7684\u5c5e\u6027\uff0c\u4f8b\u5982\uff1a<\/p>\n\n\n\n
struct OldValue1:View{\n    @State var data = MyData()\n    var body: some View{\n        Button(\"change\"){\n            data.t = Int.random(in: 1...5)\n        }\n        .onChange(of: data.t){ [data] newValue in\n            let oldValue = data.t\n            if newValue % oldValue == 2 {\n                print(\"\u4f59\u503c\u4e3a 2\")\n            } else {\n                print(\"\u4e0d\u6ee1\u8db3\u6761\u4ef6\")\n            }\n        }\n    }\n}\n\nstruct MyData{\n    var t = 0\n}<\/pre>\n\n\n\n
\u6362\u6210 [data.t] \u5c06\u63d0\u793a\u5982\u4e0b\u9519\u8bef\uff1a<\/p>\n\n\n\n
Fields may only be captured by assigning to a specific name\n<\/pre>\n\n\n\n
\u5bf9\u4e8e\u5f15\u7528\u7c7b\u578b\uff0c\u6355\u83b7\u65f6\u9700\u6dfb\u52a0weak<\/code>\u3002<\/p>\n\n\n\n
onChange \u53ef\u4ee5\u89c2\u5bdf\u54ea\u4e9b\u503c<\/h5>\n\n\n\n
\n\n\n\n
\u4efb\u4f55\u7b26\u5408 Equatable \u534f\u8bae\u7684\u7c7b\u578b\u90fd\u53ef\u88ab onChange \u6240\u89c2\u5bdf\u3002\u5bf9\u4e8e\u53ef\u9009\u503c\uff0c\u53ea\u8981 Wrapped \u7b26\u5408 Equatable \u5373\u53ef\u3002<\/p>\n\n\n\n
\u901a\u5e38\u6211\u4eec\u4f1a\u4f7f\u7528 onChange \u6765\u89c2\u5bdf@State\uff0c@StateObject \u6216@ObservableObject \u5305\u88c5\u6570\u636e\u7684\u53d8\u5316\u3002\u4f46\u5728\u67d0\u4e9b\u7279\u5b9a\u7684\u573a\u666f\u4e0b\uff0c\u6211\u4eec\u4e5f\u53ef\u4ee5\u7528 onChange \u6765\u89c2\u5bdf\u5e76\u975e\u4e3a\u89c6\u56fe Source of truth \u7684\u6570\u636e\u3002\u4f8b\u5982\uff1a<\/p>\n\n\n\n
struct NonStateDemo: View {\n    let store = Store.share\n    @State var id = UUID()\n    var body: some View {\n        VStack {\n            Button(\"refresh\") {\n                id = UUID()\n            }\n            .id(id)\n            .onChange(of: store.date) { value in\n                print(value)\n            }\n        }\n    }\n}\n\nclass Store {\n    var date = Date()\n    var cancellables = Set<AnyCancellable>()\n    init(){\n        Timer.publish(every: 3,  on: .current, in: .common)\n            .autoconnect()\n            .assign(to: \\.date, on: self)\n            .store(in: &cancellables)\n    }\n\n    static let share = Store()\n}\n<\/pre>\n\n\n\n
Store \u5e76\u975e\u53ef\u4ee5\u5f15\u53d1\u89c6\u56fe\u5237\u65b0\u7684\u5143\u7d20\uff0c\u901a\u8fc7\u70b9\u51fb Button \u6539\u53d8 id \u6765\u5237\u65b0\u89c6\u56fe\u3002<\/p>\n\n\n\n
\u672c\u4f8b\u770b\u8d77\u6765\u6709\u4e9b\u65e0\u5398\u5934\uff0c\u4f46\u5b83\u4e3a\u63ed\u793a onChange \u7684\u7279\u70b9\u63d0\u4f9b\u4e86\u5f88\u597d\u7684\u542f\u793a\u3002<\/p>\n\n\n\n
onChange \u7684\u7279\u70b9<\/h5>\n\n\n\n
\n\n\n\n
\u5728 onChange \u63a8\u51fa\u4e4b\u9645\uff0c\u5927\u591a\u6570\u4eba\u5c06\u5176\u89c6\u4e3a@State \u7684 didSet \u5b9e\u73b0\u3002\u4f46\u4e8b\u5b9e\u4e0a\u4e24\u8005\u95f4\u6709\u5f88\u5927\u7684\u5dee\u5f02\u3002<\/p>\n\n\n\n
didSet \u5728\u503c\u53d1\u751f\u6539\u53d8<\/strong>\u5373\u8c03\u7528\u95ed\u5305\u4e2d\u7684\u64cd\u4f5c\uff0c\u65e0\u8bba\u65b0\u503c\u4e0e\u65e7\u503c\u662f\u5426\u4e0d\u540c\u3002\u4f8b\u5982<\/p>\n\n\n\n
class MyStore{\n    var i = 0{\n        didSet {\n            print(\"oldValue:\\(oldValue),newValue:\\(i)\")\n        }\n    }\n}\n\nlet store = MyStore()\nstore.i = 0\n\n\/\/oldValue:0,newValue:0\n<\/pre>\n\n\n\n
onChange \u6709\u5176\u81ea\u8eab\u7684\u8fd0\u884c\u903b\u8f91\u3002<\/p>\n\n\n\n
\u5728\u4e0a\u8282\u7684\u4f8b\u5b50\u4e2d\uff0c\u5c3d\u7ba1 Store \u4e2d\u7684 date \u6bcf\u4e09\u79d2\u4f1a\u53d1\u751f\u4e00\u6b21\u6539\u53d8\uff0c\u4f46\u5e76\u4e0d\u4f1a\u5f15\u8d77\u89c6\u56fe\u7684\u91cd\u65b0\u7ed8\u5236\u3002\u901a\u8fc7\u70b9\u51fb\u6309\u94ae\u5f3a\u5236\u91cd\u7ed8\u89c6\u56fe\uff0conChange \u624d\u4f1a\u88ab\u89e6\u53d1\u3002<\/p>\n\n\n\n
\u5982\u679c\u5728\u4e09\u79d2\u4e4b\u5185\u591a\u6b21\u70b9\u51fb\u6309\u94ae\uff0c\u63a7\u5236\u53f0\u5e76\u4e0d\u4f1a\u6253\u5370\u66f4\u591a\u7684\u65f6\u95f4\u4fe1\u606f\u3002<\/p>\n\n\n\n
\u88ab\u89c2\u5bdf\u503c\u7684\u53d8\u5316\u5e76\u4e0d\u4f1a\u89e6\u53d1 onChange\uff0c\u53ea\u6709\u5728\u6bcf\u6b21\u89c6\u56fe\u91cd\u7ed8\u65f6 onChnage \u624d\u4f1a\u89e6\u53d1\u3002onChange \u89e6\u53d1\u540e\u4f1a\u6bd4\u8f83\u88ab\u89c2\u5bdf\u503c\u7684\u53d8\u5316\uff0c\u53ea\u6709\u65b0\u65e7\u503c\u4e0d\u4e00\u81f4\u65f6\uff0c\u624d\u4f1a\u8c03\u7528 onChange \u95ed\u5305\u4e2d\u7684\u64cd\u4f5c\u3002<\/strong><\/p>\n\n\n\n
\u5173\u4e8e onChange \u7684 FAQ<\/h5>\n\n\n\n
\n\n\n\n
\u89c6\u56fe\u4e2d\u53ef\u4ee5\u653e\u7f6e\u591a\u5c11\u4e2a onChange<\/strong><\/p>\n\n\n\n
\u4efb\u610f\u591a\u4e2a\u3002\u4e0d\u8fc7\u7531\u4e8e onChange \u7684\u95ed\u5305\u8fd0\u884c\u5728\u4e3b\u7ebf\u7a0b\u4e2d\uff0c\u56e0\u6b64\u6700\u597d\u9650\u5236 onChange \u7684\u4f7f\u7528\u91cf\uff0c\u907f\u514d\u5f71\u54cd\u89c6\u56fe\u7684\u6e32\u67d3\u6548\u7387\u3002<\/p>\n\n\n\n
\u591a\u4e2a onChange \u7684\u6267\u884c\u987a\u884c<\/strong><\/p>\n\n\n\n
\u4e25\u683c\u6309\u7167\u89c6\u56fe\u6811\u7684\u6e32\u67d3\u987a\u5e8f\uff0c\u4e0b\u9762\u7684\u4ee3\u7801\u4e2d\uff0conChange \u7684\u6267\u884c\u987a\u5e8f\u4e3a\u4ece\u5185\u5230\u5916\uff1a<\/p>\n\n\n\n
struct ContentView: View {\n    @State var text = \"\"\n    var body: some View {\n        VStack {\n            Button(\"Change\") {\n                text += \"1\"\n            }\n            .onChange(of: text) { _ in\n                print(\"TextField1\")\n            }\n            .onChange(of: text) { _ in\n                print(\"TextField2\")\n            }\n        }\n        .onChange(of: text, perform: { _ in\n            print(\"VStack\")\n        })\n    }\n}\n\n\/\/ Output:\n\/\/ TextField1\n\/\/ TextField2\n\/\/ VStack\n<\/pre>\n\n\n\n
\u591a\u4e2a onChange \u89c2\u5bdf\u540c\u4e00\u4e2a\u503c<\/strong><\/p>\n\n\n\n
\u5728\u4e00\u4e2a\u6e32\u67d3\u5468\u671f\u5185\uff0c\u89c2\u5bdf\u540c\u4e00\u4e2a\u503c\u7684 onChange\uff0c\u65e0\u8bba\u987a\u5e8f\u4e0e\u5426\uff0c\u83b7\u5f97\u7684\u88ab\u89c2\u5bdf\u503c\u7684\u65b0\u65e7\u503c\u5747\u76f8\u540c<\/strong>\u3002\u4e0d\u4f1a\u56e0\u4e3a\u66f4\u65e9\u987a\u5e8f\u524d\u7684 onChange \u5bf9\u503c\u7684\u5185\u5bb9\u8fdb\u884c\u66f4\u6539\u800c\u53d8\u5316\u3002<\/p>\n\n\n\n
struct InOneLoop: View {\n    @State var t = 0\n    var body: some View {\n        VStack {\n            Button(\"change\") {\n                t += 1 \/\/ t = 1\n            }\n            \/\/ onChange1\n            .onChange(of: t) { [t] newValue in\n                print(\"onChange1: old:\\(t) new:\\(newValue)\")\n                    self.t += 1\n            }\n            \/\/ onChange2\n            .onChange(of: t) { [t] newValue in\n                print(\"onChange2 old:\\(t) new:\\(newValue)\")\n            }\n        }\n    }\n}\n<\/pre>\n\n\n\n
\u8f93\u51fa\u4e3a\uff1a<\/p>\n\n\n\n
render loop\nonChange1: old:3 new:4\nonChange2 old:3 new:4\nrender loop\nonChange1: old:4 new:5\nonChange2 old:4 new:5\nrender loop\nonChange(of: Int) action tried to update multiple times per frame.\n\u5728\u6bcf\u4e2a loop \u5faa\u73af\u4e2d\uff0conChange2 \u7684\u5185\u5bb9\u5e76\u6ca1\u6709\u56e0\u4e3a onChange1 \u5bf9 t \u8fdb\u884c\u4e86\u4fee\u6539\u800c\u53d8\u5316\u3002\n\n<\/pre>\n\n\n\n
\u5728\u6bcf\u4e2a loop \u5faa\u73af\u4e2d\uff0conChange2 \u7684\u5185\u5bb9\u5e76\u6ca1\u6709\u56e0\u4e3a onChange1 \u5bf9 t \u8fdb\u884c\u4e86\u4fee\u6539\u800c\u53d8\u5316\u3002<\/p>\n\n\n\n
\u4e3a\u4ec0\u4e48 onChange \u4f1a\u62a5\u9519<\/strong><\/p>\n\n\n\n
\u5728\u4e0a\u9762\u7684\u4ee3\u7801\u4e2d\uff0c\u5728\u8f93\u51fa\u7684\u6700\u540e\uff0c\u6211\u4eec\u83b7\u5f97\u4e86onChange(of: Int) action tried to update multiple times per frame.<\/code>\u7684\u9519\u8bef\u63d0\u793a\u3002<\/p>\n\n\n\n
\u8fd9\u662f\u56e0\u4e3a\uff0c\u7531\u4e8e\u6211\u4eec\u5728 onChange \u4e2d\u5bf9\u88ab\u89c2\u5bdf\u503c\u8fdb\u884c\u4e86\u4fee\u6539\uff0c\u800c\u4fee\u6539\u5c06\u518d\u6b21\u5237\u65b0\u89c6\u56fe\uff0c\u4ece\u800c\u5bfc\u81f4\u4e86\u65e0\u9650\u5faa\u73af\u3002SwiftUI \u4e3a\u4e86\u907f\u514d app \u9501\u6b7b\u800c\u91c7\u53d6\u7684\u4fdd\u62a4\u673a\u5236\u2014\u2014\u5f3a\u5236\u4e2d\u65ad\u4e86 onChange \u7684\u7ee7\u7eed\u6267\u884c\u3002<\/p>\n\n\n\n
\u81f3\u4e8e\u5141\u8bb8\u7684\u5faa\u73af\u6b21\u6570\u6ca1\u6709\u660e\u786e\u7684\u7ea6\u5b9a\uff0c\u4e0a\u9762\u4f8b\u5b50\u4e2d\u7531 Button \u6fc0\u53d1\u7684\u53d8\u5316\u901a\u5e38\u4f1a\u9650\u5236\u5728 2 \u6b21\uff0c\u800c\u7531 onAppear \u6fc0\u53d1\u7684\u53d8\u5316\u5219\u53ef\u80fd\u5728 6-7 \u6b21\u3002<\/p>\n\n\n\n
struct LoopTest: View {\n    @State var t = 0\n    var body: some View {\n        let _ = print(\"frame\")\n        VStack {\n            Text(\"\\(t)\")\n                .onChange(of: t) { _ in\n                    t += 1\n                    print(t)\n                }\n                .onAppear(perform: { t += 1 })\n        }\n    }\n}\n<\/pre>\n\n\n\n
\u8f93\u51fa\uff1a<\/p>\n\n\n\n
 frame\n 2\n frame\n 3\n frame\n 4\n frame\n 5\n frame\n 6\n frame\n 7\n frame\n onChange(of: Int) action tried to update multiple times per frame.\n<\/pre>\n\n\n\n
\u56e0\u6b64\u6211\u4eec\u9700\u8981\u5c3d\u91cf\u907f\u514d\u5728 onChange \u4e2d\u5bf9\u88ab\u89c2\u5bdf\u503c\u8fdb\u884c\u4fee\u6539\uff0c\u5982\u786e\u6709\u5fc5\u8981\uff0c\u8bf7\u4f7f\u7528\u6761\u4ef6\u5224\u65ad\u8bed\u53e5\u6765\u9650\u5236\u66f4\u6539\u6b21\u6570\uff0c\u4fdd\u8bc1\u7a0b\u5e8f\u6309\u9884\u671f\u6267\u884c\u3002<\/p>\n\n\n\n
onChange \u7684\u66ff\u4ee3\u65b9\u6848<\/h5>\n\n\n\n
\n\n\n\n
\u672c\u8282\u4e2d\u6211\u4eec\u5c06\u4ecb\u7ecd\u51e0\u4e2a\u540c onChange \u7c7b\u4f3c\u7684\u5b9e\u73b0\uff0c\u5b83\u4eec\u540c onChange \u7684\u884c\u4e3a\u5e76\u4e0d\u5b8c\u5168\u4e00\u6837\uff0c\u6709\u5404\u81ea\u7684\u7279\u70b9\u548c\u5408\u9002\u7684\u573a\u666f\u3002<\/p>\n\n\n\n
task(id:)<\/strong><\/p>\n\n\n\n
SwiftUI 3.0 \u4e2d\u65b0\u589e\u4e86 task \u4fee\u9970\u5668\uff0ctask \u5c06\u5728\u89c6\u56fe\u51fa\u73b0\u65f6\u4ee5\u5f02\u6b65\u7684\u65b9\u5f0f\u8fd0\u884c\u95ed\u5305\u4e2d\u7684\u5185\u5bb9\uff0c\u540c\u65f6\u5728 id \u503c\u53d1\u751f\u53d8\u5316\u65f6\uff0c\u91cd\u542f\u4efb\u52a1\u3002<\/p>\n\n\n\n
\u5728 task \u95ed\u5305\u4e2d\u7684\u4efb\u52a1\u5355\u5143\u8db3\u591f\u7b80\u5355\u65f6\uff0c\u5176\u8868\u73b0\u540c onChange \u7c7b\u4f3c\uff0c\u76f8\u5f53\u4e8e onAppear + onChange \u7684\u7ec4\u5408\u3002<\/p>\n\n\n\n
struct AsyncTest: View {\n    @State var t: CGFloat = 0\n    var body: some View {\n        let _ = print(\"frame\")\n        VStack {\n            Text(\"\\(t)\")\n                .task(id: t) {\n                    t += 1\n                    print(t)\n                }\n        }\n    }\n}\n<\/pre>\n\n\n\n
\u8f93\u51fa\uff1a<\/p>\n\n\n\n
frame\n1.0\nframe\n2.0\n...\n<\/pre>\n\n\n\n
\u4f46\u6709\u4e00\u70b9\u9700\u8981\u7279\u522b\u6ce8\u610f\uff0c\u7531\u4e8e task \u7684\u95ed\u5305\u662f\u5f02\u6b65\u8fd0\u884c\u7684\uff0c\u7406\u8bba\u4e0a\u5176\u5e76\u4e0d\u4f1a\u5bf9\u89c6\u56fe\u7684\u6e32\u67d3\u9020\u6210\u5f71\u54cd\uff0c\u56e0\u6b64 SwiftUI \u5c06\u4e0d\u4f1a\u9650\u5236\u5b83\u7684\u6267\u884c\u6b21\u6570\u3002\u672c\u4f8b\u4e2d\uff0ctask \u7684\u95ed\u5305\u4e2d\u7684\u4efb\u52a1\u5c06\u4e0d\u65ad\u8fd0\u884c\uff0cText \u4e2d\u7684\u5185\u5bb9\u4e5f\u5c06\u4e0d\u65ad\u53d8\u5316\uff08\u5982\u679c\u5c06 task \u6362\u6210 onChange \u5219\u4f1a\u88ab SwiftUI \u81ea\u52a8\u4e2d\u65ad\uff09\u3002<\/p>\n\n\n\n
Combine \u7248\u672c\u7684 onChange<\/h5>\n\n\n\n
\n\n\n\n
\u5728 onChange \u6ca1\u6709\u63a8\u51fa\u4e4b\u524d\uff0c\u591a\u6570\u4eba\u4f1a\u5229\u7528 Combine \u6846\u67b6\u6765\u5b9e\u73b0\u7c7b\u4f3c onChange \u7684\u6548\u679c\u3002<\/p>\n\n\n\n
import Combine\nstruct CombineVersion: View {\n    @State var t = 0\n    var body: some View {\n        VStack {\n            Button(\"change\") {\n                t += 1\n            }\n        }\n        .onAppearAndOnChange(of: t, perform: { value in\n            print(value)\n        })\n    }\n}\n\npublic extension View {\n    func onAppearAndOnChange<V>(of value: V, perform action: @escaping (_ newValue: V) -> Void) -> some View where V: Equatable {\n        onReceive(Just(value), perform: action)\n    }\n}<\/pre>\n\n\n\n
\u5b83\u7684\u884c\u4e3a\u7c7b\u4f3c onAppear + onChange \u7684\u7ec4\u5408\u3002\u6700\u5927\u7684\u4e0d\u540c\u662f\uff0c\u6b64\u79cd\u65b9\u6848\u5e76\u4e0d\u4f1a\u6bd4\u8f83\u88ab\u89c2\u5bdf\u503c\u662f\u5426\u53d1\u751f\u6539\u53d8\uff08\u65b0\u65e7\u503c\u4e0d\u4e00\u6837\uff09\u3002<\/p>\n\n\n\n
struct CombineVersion: View {\n    @State var t = 0\n    @State var n = 0\n    var body: some View {\n        VStack {\n            Text(\"\\(n)\")\n            Button(\"change n\"){\n                n += 1\n                t += 0\n            }\n        }\n        .onAppearAndOnChange(of: t, perform: { value in\n            print(\"combine \\(t)\")\n        })\n        .onChange(of: t){ value in\n            print(\"onChange \\(t)\")\n        }\n    }\n}\n<\/pre>\n\n\n\n
onChange \u7684\u95ed\u5305\u56e0\u4e3a t \u7684\u5185\u5bb9\u6ca1\u6709\u53d1\u751f\u53d8\u5316\u5c06\u4e0d\u4f1a\u88ab\u8c03\u7528\uff0c\u800c onAppearAndOnChange \u7684\u95ed\u5305\u5c06\u5728\u6bcf\u6b21 t \u8d4b\u503c\u65f6\u5747\u88ab\u8c03\u7528\u3002<\/p>\n\n\n\n
\u6709\u7684\u65f6\u5019\uff0c\u8fd9\u79cd\u884c\u4e3a\u6070\u662f\u6211\u4eec\u6240\u9700\u7684\u3002<\/p>\n\n\n\n
Binding \u7248\u672c\u7684 onChange<\/h5>\n\n\n\n
\n\n\n\n
\u6b64\u79cd\u65b9\u5f0f\u53ea\u80fd\u9488\u5bf9 Binding \u7c7b\u578b\u7684\u6570\u636e\uff0c\u901a\u8fc7\u5728 Binding \u7684 Set \u4e2d\u6dfb\u52a0\u4e00\u5c42\u903b\u8f91\uff0c\u5b9e\u73b0\u5bf9\u5185\u5bb9\u53d8\u5316\u7684\u54cd\u5e94\u3002<\/p>\n\n\n\n
extension Binding {\n    func didSet(_ didSet: @escaping (Value) -> Void) -> Binding<Value> {\n        Binding(get: { wrappedValue },\n                set: { newValue in\n                    self.wrappedValue = newValue\n                    didSet(newValue)\n                })\n    }\n}\n\nstruct BindingVersion2: View {\n    @State var text = \"\"\n    var body: some View {\n        Form {\n            TextField(\"text:\", text: $text.didSet { print($0) })\n        }\n    }\n}<\/pre>\n\n\n\n
\u53ef\u80fd\u4f60\u4f1a\u89c9\u5f97\u591a\u6b64\u4e00\u4e3e\uff0c\u5b8c\u5168\u53ef\u4ee5\u4f7f\u7528 onChange \u6765\u5b9e\u73b0\uff0c\u4f46\u91c7\u7528 Binding \u7684\u65b9\u5f0f\u8ba9\u6211\u4eec\u6709\u4e86\u5728\u6570\u636e\u4fee\u6539\u524d<\/strong>\u8fdb\u884c\u5224\u65ad\u64cd\u4f5c\u7684\u53ef\u80fd\uff0c\u4f7f\u7528\u5f97\u5f53\u5c06\u6781\u5927\u5730\u51cf\u5c11\u89c6\u56fe\u7684\u5237\u65b0\u3002<\/p>\n\n\n\n
\u4f8b\u5982\uff0c\u6211\u4eec\u8fd8\u53ef\u4ee5\u5bf9\u65b0\u6570\u636e\u8fdb\u884c\u63d0\u524d\u5224\u65ad\u4ee5\u51b3\u5b9a\u662f\u5426\u66f4\u6539\u539f\u503c\uff1a<\/p>\n\n\n\n
extension Binding {\n    func conditionSet(_ condition: @escaping (Value) -> Bool) -> Binding<Value> {\n        Binding(get: { wrappedValue },\n                set: { newValue in\n                    if condition(newValue) {\n                        self.wrappedValue = newValue\n                    }\n                })\n    }\n}\n<\/pre>\n\n\n\n
\u8bf7\u6ce8\u610f\uff0c\u6b64\u79cd\u65b9\u5f0f\u5e76\u4e0d\u80fd\u540c\u652f\u6301 Binding \u7684\u7cfb\u7edf\u63a7\u4ef6\u5f88\u597d\u7684\u914d\u5408\u4f7f\u7528\uff0c\u56e0\u4e3a\u7cfb\u7edf\u63a7\u4ef6\u5e76\u4e0d\u4f1a\u56e0\u4e3a\u6211\u4eec\u9650\u5236\u4e86\u6570\u503c\u7684\u4fee\u6539\u800c\u4ea7\u751f\u5bf9\u5e94\u7684\u6548\u679c\uff08\u7cfb\u7edf\u63a7\u4ef6\u4e2d\u8fd8\u4fdd\u7559\u4e86\u4e00\u5957\u81ea\u5df1\u7684\u6570\u636e\uff0c\u9664\u975e\u5f3a\u5236\u5237\u65b0\u89c6\u56fe\uff0c\u5426\u5219\u5e76\u4e0d\u4f1a\u4fdd\u8bc1\u540c\u5916\u90e8\u7684\u6570\u636e\u5b8c\u5168\u540c\u6b65\uff09\u3002\u4f8b\u5982\u4e0b\u9762\u7684\u4ee3\u7801\uff0c\u8868\u73b0\u540c\u4f60\u9884\u671f\u7684\u884c\u4e3a\u4f1a\u6709\u51fa\u5165\u3002<\/p>\n\n\n\n
struct BindingVersion3: View {\n    @State var text = \"\"\n    var body: some View {\n        Form {\n            Text(text)\n            TextField(\"text:\", text: $text.conditionSet { text in\n                return text.count < 5\n            })\n        }\n    }\n}\n<\/pre>\n\n\n\n
\u603b\u7ed3<\/h5>\n\n\n\n
\n\n\n\n
onChange \u4e3a\u6211\u4eec\u5728\u89c6\u56fe\u4e2d\u8fdb\u884c\u903b\u8f91\u5904\u7406\u63d0\u4f9b\u4e86\u4fbf\u5229\uff0c\u4e86\u89e3\u5b83\u7684\u7279\u70b9\u4e0e\u9650\u5236\uff0c\u9009\u62e9\u5408\u9002\u7684\u573a\u666f\u4f7f\u7528\u5b83\u3002\u5728\u5fc5\u8981\u7684\u60c5\u51b5\u4e0b\uff0c\u5c06\u903b\u8f91\u5904\u7406\u4e0e\u89c6\u56fe\u5206\u79bb\uff0c\u4ee5\u4fdd\u8bc1\u89c6\u56fe\u7684\u6e32\u67d3\u6548\u7387\u3002<\/p>\n\n\n\n
\u5e0c\u671b\u672c\u6587\u5bf9\u4f60\u6709\u6240\u5e2e\u52a9\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u8f6c\u8f7d\uff1ahttps:\/\/www.fatbobman.com\/posts\/onChange\/ \u4ece iOS 14 \u5f00 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"_links":{"self":[{"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/posts\/4767"}],"collection":[{"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/92it.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=4767"}],"version-history":[{"count":4,"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/posts\/4767\/revisions"}],"predecessor-version":[{"id":4771,"href":"https:\/\/92it.top\/index.php?rest_route=\/wp\/v2\/posts\/4767\/revisions\/4771"}],"wp:attachment":[{"href":"https:\/\/92it.top\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4767"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/92it.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4767"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/92it.top\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4767"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}