Canvas渲染View，Console提供正确的输出，但应用程序中的View保持为空

Question

在MacOS上，我有一个非常简单的ContentView:

struct ContentView: View {

@ObservedObject var environment: Environment

var body: some View {

if let glyph = environment.glyph {
print ("Content View (glyph)")
return AnyView {
GlyphView(glyph: glyph)
}
} else {
return AnyView {
Text("no glyph")
}
}
}
}
struct ContentView_Previews: PreviewProvider {
static var environment = Environment()
static var previews: some View {
ContentView(environment: environment)
}
}

当我运行应用程序时，控制台给出：

2020-10-14 21:50:42.065365+0200 ShapeSearch[94679:5992139] Metal API Validation Enabled
2020-10-14 21:50:42.093298+0200 ShapeSearch[94679:5992191] flock failed to lock maps file: errno = 35
2020-10-14 21:50:42.093688+0200 ShapeSearch[94679:5992191] flock failed to lock maps file: errno = 35
Content View Glyph "k" - 6 contours

并且ContentView保持为空，没有GlyphView，没有Text。

但当我调试GlyphView时，我可以在画布上看到非常好的渲染字形：

struct GlyphView_Previews: PreviewProvider {

static var glyph = Environment().glyph!
static var previews: some View {
GlyphView(glyph: glyph)
}
}

CCD_ 6在两种情况下都取自同一来源。我确信。

编辑：

这种工作方式：

struct ContentView: View {

@ObservedObject var environment: Environment

var body: some View {
GlyphView(glyph: environment.glyph!)
}
}

错误可能在哪里？

Answer 1

目前尚不清楚您使用的是哪个SwiftUI版本，但以下内容在任何情况下都应该适用于

var body: some View {
Group {  
if nil != environment.glyph {
GlyphView(glyph: environment.glyph!)
} else {
Text("no glyph")
}
}
}