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Replicate 12 UIKit's contentMode options in SwiftUI

 4 years ago
source link: https://sarunw.com/posts/uikits-contentmode-in-swiftui/
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Replicate 12 UIKit's contentMode options in SwiftUI

12 Apr 2021 ⋅ 4 min read ⋅ SwiftUI Image Resize
Table of Contents

There are twelve way[1] to transform image in UIImageView with content mode, but we got only two content mode in SwiftUI. But, we can replicate most of them with a combination of two modifier aspectRatio(_:contentMode:) and frame(width:height:alignment:).

This is the list of UIKit's contentMode. You can visit my previous post to see what these property are.

Throughout this post, I will use two images, a big image with a size of 240x300[2] and a smaller image with a size of 80x100. You will see how each image reacts to the same content mode.

large image (240x300)large image (240x300)small image (80x100)small image (80x100)

I will put them side-by-side in image views of size 200x200. I also add a pink border for you to visualize the behavior easily. Here is our testing code.

struct ContentView: View {
    var body: some View {
        HStack(spacing: 200) {
            Image("contentmode-large")
                .resizable()
                .frame(width: 200, height: 200)
                .border(Color.pink)
            Image("contentmode-small")
                .resizable()
                .frame(width: 200, height: 200)
                .border(Color.pink)
        }
    }
}

In the examples below, I will only code for the large image for brevity.

Scaling

scaleToFill

scaleToFill scales the content to fill the view's bounds without maintaining the aspect ratio. We can do this in SwiftUI with .resizable() modifier.

Image("contentmode-large")
    .resizable()
    .frame(width: 200, height: 200)
    .border(Color.pink)
scaleToFillscaleToFill

scaleAspectFit

scaleAspectFit scales the content to fit within the view's bounds and maintaining the aspect ratio. This might leave an empty space on one axis. We do this in SwiftUI with resizable() and .aspectRatio(contentMode: .fit) (or .scaledToFit()).

Image("contentmode-large")
    .resizable()
    .aspectRatio(contentMode: .fit) // 1
    .frame(width: 200, height: 200)
    .border(Color.pink)
Image("contentmode-small")
    .resizable()
    .scaledToFit() // 2
    .frame(width: 200, height: 200)
    .border(Color.pink)

You can use .aspectRatio(contentMode: .fit) <1> or shorthand version, .scaledToFit() <2>.

scaleAspectFitscaleAspectFit

scaleAspectFill

scaleAspectFill scales the content to fill the view's bounds and maintaining the aspect ratio. This might cause some portion of the image to extend beyond the view's bounds. We do this in SwiftUI with resizable() and .aspectRatio(contentMode: .fill) (or .scaledToFill()).

Image("contentmode-large")
    .resizable()
    .aspectRatio(contentMode: .fill)
    .frame(width: 200, height: 200)
    .border(Color.pink)
Image("contentmode-small")
    .resizable()
    .scaledToFill()
    .frame(width: 200, height: 200)
    .border(Color.pink)
scaleAspectFillscaleAspectFill mobileatscale.png

Positioning

We have nine mode to position an image. Each mode will pin the image to the respective position without scaling the image. For example, center will pin the content's center to the view's center, top will pin the content's top to the view's top.

Since we don't need to scale the image, we don't need .resizable() and .aspectRatio() here. We can rely on alignment parameter of .frame(width:height:alignment:).

center 

Image("contentmode-large")
    .frame(width: 200, height: 200, alignment: .center)
    .border(Color.pink)
centercenter
Image("contentmode-large")
    .frame(width: 200, height: 200, alignment: .top)
    .border(Color.pink)
toptop

bottom 

Image("contentmode-large")
    .frame(width: 200, height: 200, alignment: .bottom)
    .border(Color.pink)
bottombottom
Image("contentmode-large")
    .frame(width: 200, height: 200, alignment: .leading)
    .border(Color.pink)
leftleft

right 

Image("contentmode-large")
    .frame(width: 200, height: 200, alignment: .trailing)
    .border(Color.pink)
rightright

topLeft 

Image("contentmode-large")
    .frame(width: 200, height: 200, alignment: .topLeading)
    .border(Color.pink)
topLefttopLeft

topRight 

Image("contentmode-large")
    .frame(width: 200, height: 200, alignment: .topTrailing)
    .border(Color.pink)
topRighttopRight

bottomLeft 

Image("contentmode-large")
    .frame(width: 200, height: 200, alignment: .bottomLeading)
    .border(Color.pink)
bottomLeftbottomLeft

bottomRight 

Image("contentmode-large")
    .frame(width: 200, height: 200, alignment: .bottomTrailing)
    .border(Color.pink)
bottomRightbottomRight

As you can see, the only difference here is we use leading instead of left and trailing instead of right.

  1. I didn't put .redraw into consideration here since it is not modify position or size of an image. More detail here ↩︎

  2. Photo by Mae Mu on Unsplash ↩︎

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