Updating Path in SwiftUI - ios

Question

I have got a SwiftUI View with a chart which is made using Path and data from entries array.
The code:
struct TodayChartView: View {
var body: some View {
GeometryReader { reader in
Path { p in
for i in 1..<entries.count {
p.move(to: CGPoint(x: entries[i-1].x, entries[i-1].y: y))
p.addLine(to: CGPoint(entries[i].x: x, entries[i].y: y))
}
}
}.stroke(Color.blue, style: StrokeStyle(lineWidth: 3, lineCap: .round, lineJoin: .round))
}
}
When user presses the button in another View, a new entry is added to entries and I want to display it on my Path. So, basically, I need to somehow trigger redrawing it. Is there any way to achieve it?

Answer 1

Pass the entries as a parameter to TodayChartView. With the entries as a #State var in ContentView, the TodayChartView gets redrawn whenever entries changes.
Here is a complete example (tested in Xcode 11.7):
struct TodayChartView: View {
let entries: [CGPoint]
var body: some View {
// GeometryReader { reader in
Path { p in
for i in 1..<self.entries.count {
p.move(to: CGPoint(x: self.entries[i-1].x, y: self.entries[i-1].y))
p.addLine(to: CGPoint(x: self.entries[i].x, y: self.entries[i].y))
}
}
.stroke(Color.blue, style: StrokeStyle(lineWidth: 3, lineCap: .round, lineJoin: .round))
// }
}
}
struct ContentView: View {
#State private var entries: [CGPoint] = [CGPoint(x: 150, y: 150)]
var body: some View {
VStack(spacing: 20) {
Button("Add Point") {
let x = CGFloat.random(in: 0...300)
let y = CGFloat.random(in: 0...300)
self.entries.append(CGPoint(x: x, y: y))
}
TodayChartView(entries: self.entries)
.frame(width: 300, height: 300)
}
}
}
Note: Your TodayChartView is not currently using GeometryReader so I've commented it out.

Answer 2

Try this one
Path { p in
for i in 1..<entries.count {
p.move(to: CGPoint(x: entries[i-1].x, entries[i-1].y: y))
p.addLine(to: CGPoint(entries[i].x: x, entries[i].y: y))
}
}
}.stroke(Color.blue, style: StrokeStyle(lineWidth: 3, lineCap: .round, lineJoin: .round))
.id(entries) // << here !!