我最近遇到需要编写一个 MockClass
,因为它会导致 SwiftUIpreview
从工作中。不幸的是,我收到错误:
Property type 'T' does not match that of the 'wrappedValue' property of its wrapper type 'EnvironmentObject'
在视图结构中:
struct ContentView<T>: View {
@EnvironmentObject var mockFoobar: T
...
}
还有错误:
Type of expression is ambiguous without more context
对于预览结构:
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
let mockFoobar: MockFoobar = MockFoobar()
return ContentView<MockFoobar>()
.environmentObject(mockFoobar)
}
}
MockFoobar 类是:
class MockFoobar: ObservableObject {
...
}
正如用户@Asperi 善意提供的,按照建议测试了以下内容:
class Foobar: ObservableObject {
@Published var param: Bool = false
func start() {
self.param = true
}
}
struct MyFoobarView<T: ObservableObject>: View {
@EnvironmentObject var foobar: T
var body: some View {
VStack {
Text("Hello Foobar")
}
.onAppear {
self.foobar.start()
}
}
}
struct MyFoobarView_Previews: PreviewProvider {
static var previews: some View {
let foobar: Foobar = Foobar()
return MyFoobarView()
.environmentObject(foobar)
}
}
但我收到以下错误(第一个错误.onAppear
第二个在 PreviewProvider 中):
Cannot call value of non-function type 'Binding<Subject>'
Generic parameter 'T' could not be inferred