SwiftUI:拖动逻辑出错还是这是一个错误? [英] SwiftUI: Error in dragging logic or is this a bug?

问题描述

SwiftUI 处于测试阶段，所以这可能是一个错误，但我在其他 YouTube 视频中看到过类似的东西，所以也许不是，测试非常简单.我正在创建一个可以水平拖动的圆圈.

SwiftUI is in beta, so maybe this is a bug, but I've seen something like this working in others YouTube videos so perhaps it's not, the test is pretty simple. I'm creating a circle I can drag around on horizontally.

import SwiftUI

struct ContentView : View {
    @State private var location = CGPoint.zero
    var body: some View {
        return Circle()
            .fill(Color.blue)
            .frame(width: 300, height: 300)
            .gesture(
                DragGesture(minimumDistance: 10)
                    .onChanged { value in
                        print("value.location")
                        print(value.location)
                        self.location = CGPoint(
                            x: value.location.x,
                            y: 0)
                }
        )
            .offset(x: self.location.x, y: self.location.y)
    }
}

#if DEBUG
struct ContentView_Previews : PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}
#endif

这会导致行为:

据我所知，DragGesture onChanged 回调中的 value.location 值不应该像这样在数字之间波动.查看日志，数字到处都是.我错过了什么吗?

As far as I can tell, the value.location value in the DragGesture onChanged callback shouldn't be fluctuating between numbers like this. Looking at the logs the numbers are all over the place. Am I missing something?

推荐答案

DragGesture 的默认 CoordinateSpace 是 .local，这是Circle 内的坐标空间.当您移动 Circle 时会发生什么?由于您的手指没有移动，您的手指在 Circle 的几何图形中的位置突然发生了变化，从而导致 Circle 再次移动.重复恶心.

DragGesture's default CoordinateSpace is .local, which is the coordinate space inside your Circle. What happens when you move the Circle? Since your finger doesn't move, the location of your finger in the Circle's geometry suddenly changes, which causes the Circle to move again. Repeat ad nauseum.

尝试使用CoordinateSpace.global:

DragGesture(minimumDistance: 10, coordinateSpace: .global)

您可能还想使用 value.translation 而不是 value.location 来避免手指向下时的初始跳跃.

You'll probably also want to use value.translation instead of value.location to avoid the initial jump when you put your finger down.

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