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Why I Cannot Add Variable to GeometryReader{} Closure Argument
by [email protected]July 11th, 2020
Too Long; Didn't Read
A programmer has been using Javascrift for the past two years. He wants to use a GeometryReader{} to contain a view, so he can decide the position of the view base on the parent container property such as size, coordinates space, ect... But he gets an error like this: "Why I can not write variable inside a closure?" He then encountered another issue, Generic parameter`Content`could not be infered. So, I explicitly specify the arguments to fix this issue.Companies Mentioned
I want to use a GeometryReader{} to contain a view, so I can decide the position of the view base on the parent container property such as size, coordinates space, ect...
So, I have some code like this:
GeometryReader {
geometry in
self.badgeSymbols
.scaleEffect(1.0 / 4.0, anchor: .top)
.position(x: geometry.size.width / 2.0,
y: (3.0 / 4.0) * geometry.size.height)
}GeometryReader {
geometry in
var width = geometry.size.width ;
var height = geometry.size.height;
self.badgeSymbols
.scaleEffect(1.0 / 4.0, anchor: .top)
.position(x: width / 2.0,
y: (3.0 / 4.0) * height)
}It should work just fine according to my knowledge.
How ever I get an error like this:
Encounter a strange error, I went to google the answer.
And following is my found:
1. Curly braces`{ ...body...}` after the GeometryReader is a syntax called closure. In this case, we call GeometryReader to initialize a GeometryReader instance. According to the Documentation of GeometryReader by Apple.
When we instantiate a type, and there is only one parameter, this parameter happens to be a function.Type, we can GeometryReader followed by {}function (Closure function).
2. Why I can not write variable inside a closure? Soon I realised I asked the wrong question.
Yes, I can write variable inside a closure.
I was writing a variable inside a return sentence. When there is no return keyword in the statements section, the whole section will be treated as a return statement. I can not write new variable inside the return statement.
So, I added a return keyword to teturn my view.
GeometryReader {
geometry in
var width = geometry.size.width ;
var height = geometry.size.height;
self.badgeSymbols
.scaleEffect(1.0 / 4.0, anchor: .top)
.position(x: geometry.size.width / 2.0, y: (3.0 / 4.0) * geometry.size.height)
return Text("Position:x: \(geometry.size.width / 2.0) y: \((3.0 / 4.0) * geometry.size.height))")
}Now I encountered another issue, Generic parameter`Content`could not be infered. So, I explicitly specify the arguments to fix this issue. It goes like this:
GeometryReader<Text> {
geometry in
var width = geometry.size.width ;
var height = geometry.size.height;
self.badgeSymbols
.scaleEffect(1.0 / 4.0, anchor: .top)
.position(x: geometry.size.width / 2.0, y: (3.0 / 4.0) * geometry.size.height)
return Text("Position:x: \(geometry.size.width / 2.0) y: \((3.0 / 4.0) * geometry.size.height))")
}The reason being that, GeometryReader.Type has a generic parameter defined by Apple developer... It is stated like this:
@frozen struct GeometryReader<Content> where Content : ViewSimple Explanation: I provide a type that conforms the View Protocol, the compilation will pass.
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