一个视图中的多个警报只能在 swiftui 中始终使用最后一个警报
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【中文标题】一个视图中的多个警报只能在 swiftui 中始终使用最后一个警报【英文标题】：Multiple Alerts in one view can only the last alert works always in swiftui 【发布时间】：2019-12-18 21:03:48 【问题描述】：如果布尔值为真，我有两个警报。
Alert - 1 - 如果蓝牙状态有任何问题而不是开机，就会调用它。这直接从名为 BLE 的 swift 包中调用。代码sn-p如下。
Alert - 2 - 当您想要取消配对外围设备时调用它，为用户提供两个选项。取消配对或保持在同一页面上。
问题： 两个警报似乎都工作正常，但如果它们没有放在同一个视图中。当我将警报放在同一个视图中时，最后显示的警报会按从上到下的顺序调用。
操作系统会读取第一个警报，但只有在调用第二个警报时才会激活它。
如果它们被调用，是否有办法使两个警报都起作用。 我提到了下面的解决方案，但我得到了相同的结果。
Solution 1 和 Solution 2
有2个代码sn-ps
1.主要应用
import SwiftUI
import BLE
struct Dashboard: View
@EnvironmentObject var BLE: BLE
@State private var showUnpairAlert: Bool = false
private var topLayer: HeatPeripheral
self.BLE.peripherals.baseLayer.top
var body: some View
VStack(alignment: .center, spacing: 0)
// MARK: - Menu Bar
VStack(alignment: .center, spacing: 4)
Button(action:
print("Unpair tapped!")
self.showUnpairAlert = true
)
HStack
Text("Unpair")
.fontWeight(.bold)
.font(.body)
.frame(minWidth: 85, minHeight: 35)
.cornerRadius(30)
.onAppear(perform:
self.BLE.update()
)
// Alert 1 - It is called if it meets one of the cases and returns the alert
// It is presented in the function centralManagerDidUpdateState
.alert(isPresented: $BLE.showStateAlert, content: () -> Alert in
let state = self.BLE.centralManager!.state
var message = ""
switch state
case .unknown:
message = "Bluetooth state is unknown"
case .resetting:
message = "Bluetooth is resetting..."
case .unsupported:
message = "This device doesn't have a bluetooth radio."
case .unauthorized:
message = "Turn On Bluetooth In The Settings App to Allow Battery to Connect to App."
case .poweredOff:
message = "Turn On Bluetooth to Allow Battery to Connect to App."
break
@unknown default:
break
return Alert(title: Text("Bluetooth is \(self.BLE.getStateString())"), message: Text(message), dismissButton: .default(Text("OK")))
)
// Alert 2 - It is called when you tap the unpair button
.alert(isPresented: $showUnpairAlert)
Alert(title: Text("Unpair from \(checkForDeviceInformation())"), message: Text("*Your peripheral command will stay on."), primaryButton: .destructive(Text("Unpair"))
self.unpairAndSetDefaultDeviceInformation()
, secondaryButton: .cancel())
func unpairAndSetDefaultDeviceInformation()
defaults.set(defaultDeviceinformation, forKey: Keys.deviceInformation)
disconnectPeripheral()
print("Pod unpaired and view changed to Onboarding")
self.presentationMode.wrappedValue.dismiss()
DispatchQueue.main.async
self.activateLink = true
func disconnectPeripheral()
if skiinBLE.peripherals.baseLayer.top.cbPeripheral != nil
self.skiinBLE.disconnectPeripheral()
2。 BLE 包
import SwiftUI
import Combine
import CoreBluetooth
public class BLE: NSObject, ObservableObject
public var centralManager: CBCentralManager? = nil
public let baseLayerServices = "XXXXXXXXXXXXXXX"
let defaults = UserDefaults.standard
@Published public var showStateAlert: Bool = false
public func start()
self.centralManager = CBCentralManager(delegate: self, queue: nil, options: nil)
self.centralManager?.delegate = self
public func getStateString() -> String
guard let state = self.centralManager?.state else return String()
switch state
case .unknown:
return "Unknown"
case .resetting:
return "Resetting"
case .unsupported:
return "Unsupported"
case .unauthorized:
return "Unauthorized"
case .poweredOff:
return "Powered Off"
case .poweredOn:
return "Powered On"
@unknown default:
return String()
extension BLE: CBCentralManagerDelegate
public func centralManagerDidUpdateState(_ central: CBCentralManager)
print("state: \(self.getStateString())")
if central.state == .poweredOn
self.showStateAlert = false
if let connectedPeripherals = self.centralManager?.retrieveConnectedPeripherals(withServices: self.baseLayerServices), connectedPeripherals.count > 0
print("Already connected: \(connectedPeripherals.map$0.name), self.peripherals: \(self.peripherals)")
self.centralManager?.stopScan()
else
print("scanForPeripherals")
self.centralManager?.scanForPeripherals(withServices: self.baseLayerServices, options: nil)
else
self.showStateAlert = true // Alert is called if there is any issue with the state.
谢谢！！！
【问题讨论】：
【参考方案1】：要记住的是，视图修饰符实际上并不只是修改视图，它们会返回一个全新的视图。所以第一个alert 修饰符返回一个以第一种方式处理警报的新视图。第二个alert 修饰符返回一个新视图，它以第二种方式修改警报（覆盖第一种方法），这是唯一最终生效的方式。最外层的修饰符才是最重要的。
您可以尝试几件事，首先尝试将不同的警报修饰符附加到两个不同的视图，而不是同一个视图。
其次，您可以尝试alert 的替代形式，它采用可选的 Identifiable 绑定并将其传递给闭包。当 value 为 nil 时，什么都不会发生。当状态变为 nil 以外的状态时，应该会出现警报。
这是一个使用alert(item:) 形式的示例，而不是基于布尔的alert(isPresented:)。
enum Selection: Int, Identifiable
case a, b, c
var id: Int rawValue
struct MultiAlertView: View
@State private var selection: Selection? = nil
var body: some View
HStack
Button(action:
self.selection = .a
) Text("a")
Button(action:
self.selection = .b
) Text("b")
.alert(item: $selection) (s: Selection) -> Alert in
Alert(title: Text("selection: \(s.rawValue)"))
【讨论】：
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