DEV Community: Liang Wang

defer

Liang Wang — Sun, 08 Jun 2025 19:39:28 +0000

I am using photoPicker to select an image from photo library, and before using defer, my code looks like this

PhotosPicker(selection: $selectedItem, matching: .images) {
                            Label("Select an image", systemImage: "photo")
                        }
                        .onChange(of: selectedItem) { _, newValue in
                            isLoadingImage = true
                            Task {
                                    if let data = try? await newValue?.loadTransferable(type: Data.self) {
                                        selectedImageData = data

                                        if let selectedImageData, let uiImage = UIImage(data: selectedImageData) {
                                            inputImage = uiImage
                                        }
                                    }
                                isLoadingImage = false
                            } //: Task
                        } //: onChange

After using defer and change try? to do { try } catch { }, my code now looks like this

PhotosPicker(selection: $selectedItem, matching: .images) {
                            Label("Select an image", systemImage: "photo")
                        }
                        .onChange(of: selectedItem) { _, newValue in
                            Task {
                                isLoadingImage = true
                                defer { isLoadingImage = false }

                                do {
                                    if let data = try await newValue?.loadTransferable(type: Data.self) {
                                        selectedImageData = data

                                        if let selectedImageData, let uiImage = UIImage(data: selectedImageData) {
                                            inputImage = uiImage
                                        }
                                    }
                                } catch {
                                    print("Failed to load image: \(error.localizedDescription)")
                                }
                            } //: Task
                        } //: onChange

do try catch

Liang Wang — Sun, 08 Jun 2025 19:37:40 +0000

use do { try ... } catch { ... }
or ignore the error just by using try?

do {
    try modelContext.save()
    print("Item updated.")
} catch {
    print("Failed to edit item: \(error.localizedDescription)")
}

or just use try? modelContext.save()

Non-sendable result type cannot be sent from nonisolated context in call to instance method

Liang Wang — Thu, 05 Jun 2025 20:39:39 +0000

My class: Element

** The Problem:**
Non-sendable result type '[Element]' cannot be sent from nonisolated context in call to instance method 'fetchData(from:)'; this is an error in the Swift 6 language mode

Solution:
Mark class Element as final, and conform to protocol Sendable.

New problem:
Stored property '_id' of 'Sendable'-conforming class '...' is mutable

New Solution:
use @unchecked Sendable

Link: https://blog.vapor.codes/posts/fluent-models-and-sendable/

TabView array id

Liang Wang — Sat, 31 May 2025 10:38:44 +0000

TabView items need to have a unique and persistent ID for the item in each tab view to swipe.

It cannot be computed property.

iOS 18.4 Simulator Error

Liang Wang — Fri, 30 May 2025 23:21:44 +0000

TL: DR
Use a physical iPhone or an older simulator if you are having trouble using the latest iOS 18.4 simulator parsing data.

Background

I am working on an iOS app that uses Firebase Hosting for my json files and images, I want to load the data and cache them in SwiftData. In the beginning I thought Firebase Hosting works great for me, simple firebase deploy is all that needed to keep the files updated, no more git commits for Github pages where I used to store the files.

But, there can be problem with Firebase Hosting CDN caching the files, so it is best the set firebase no-cache.

Then in my iPhone 16 Pro iOS 18.4 simulator, I noticed that the json data could not be parsed. I tried with several simulators of iOS 18.4, all have the same problem. But there is no problem of fetching and parsing data when I use a physical iPhone with iOS 18.4.

Research

Later I find out that this is a known issue with the latest macOS and iOS simulators, especially with Xcode 15.3+ and macOS Sonoma.

My simulator logs show:
• network connection was lost
• no local endpoint
• Server protocol violation
• SwiftData warning about ModelContext on the wrong thread
• It fails on the macOS target or newer iOS simulators, but works fine on older simulators like iOS 18.0 / iPhone 12 Pro.

Solution

So now I stick with the iPhone 12 Pro simulator on iOS 18.0 while Apple and Firebase resolve the instability on newer platforms.

Today I learned

Liang Wang — Thu, 08 May 2025 12:50:21 +0000

Today I learned

Use Azure key vault to store secrets there, such as sensitive information like this: process.env.AzureToken
Set up azure pipeline for playwright to run at 7AM
Add Eslint for typescript and playwright

Tip:
When set up azure pipeline for playwright, remember that it needs to be in the right working directory, otherwise npm ci can not find the package-lock.json file and cannot run.

Add SwiftLint to Xcode 15.4 on M1 Mac

Liang Wang — Tue, 06 Aug 2024 18:09:17 +0000

I noticed that SwiftLint no longer works for me in Xcode 15.4 when I switched to a M1 Mac, so I searched and found this user script that has helped me to resolve this problem.

Install SwiftLint

brew install swiftlint

Add new run script phrase

if [[ "$(uname -m)" == arm64 ]]; then
    export PATH="/opt/homebrew/bin:$PATH"
fi

if which swiftlint > /dev/null; then
  swiftlint --fix && swiftlint
else
  echo "warning: SwiftLint not installed, download from https://github.com/realm/SwiftLint"
fi

Disable User Script Sandboxing
Do not forget to disable User Script Sandboxing in Build Settings/Build options, which is enabled by default from XCode 15.

Swiftlint rules
Update the line_length warning and error so it works for you.

disabled_rules:
- trailing_whitespace
opt_in_rules:
- empty_count
- empty_string
excluded:
- Carthage
- Pods
- SwiftLint/Common/3rdPartyLib
line_length:
    warning: 300
    error: 500
    ignores_function_declarations: true
    ignores_comments: true
    ignores_urls: true
function_body_length:
    warning: 300
    error: 500
function_parameter_count:
    warning: 10
    error: 15
type_body_length:
    warning: 300
    error: 500
file_length:
    warning: 1000
    error: 1500
    ignore_comment_only_lines: true
cyclomatic_complexity:
    warning: 15
    error: 25
reporter: "xcode"

SwiftLint disable rule
For example, // swiftlint:disable:next identifier_name

Custom VS Code hot key

Liang Wang — Thu, 02 May 2024 11:26:08 +0000

I would like to set up my own hot key to run and to cancel current test file.

First, press ctrl K ctrl S to show the keyboard shortcuts

To set up hotkey for run current test file

search for "Run tests in current file" to find "testing.runCurrentFile" command
press "Enter" to change keybinding to your own hotkey, i.e. "Shift + Alt + R"

To set up hotkey for cancel current test file

search for "Cancel run" to find "testing.cancelRun" command
press "Enter" to change keybinding to your own hotkey, i.e. "Shift + Alt + S"

So now you can use your own hotkey to start test run and cancel test run if it hangs.

Global Git configuration

Liang Wang — Thu, 11 Apr 2024 14:21:54 +0000

git config --list

Alias I use

alias.br=branch
alias.co=checkout
alias.cm=commit
alias.st=status
alias.last=log -3 --color --graph --pretty=format:'%Cred%h%Creset %C(yellow)%d%Creset %n%s %n%Cgreen(%cr) %n%C(bold blue)<%an>%Creset%n' --abbrev-commit --branches

Disable auto line break in VS Code

Liang Wang — Mon, 19 Feb 2024 08:54:17 +0000

To disable the auto line break in the VS code.
Are you struggling to disable the auto line break in vs code from the Prettier extension? If yes this is for you :)

Open vs code => Code => Preferences => Settings => In the search field type: Prettier
Now from the provided Prettier settings, choose the Prettier: Print Width

Screenshot
And Instead of 80, you can make it a big number. Eg: 999999
Now you don't have to worry about the line break.

link

npm

Liang Wang — Sat, 17 Feb 2024 09:35:03 +0000

Install node on Mac
n

n is a simple to use Node.js version manager for Mac and Linux. Specify the target version to install using a rich syntax, or select from a menu of previously downloaded versions. The versions are installed system-wide or user-wide, and for more targeted use you can run a version directly from the cached downloads.

See the homepage for install methods (bootstrap, npm, Homebrew, third-party), and all the usage details.

If you already have npm then installing n and then the newest LTS node version is as simple as:

npm install -g n
n lts

Playwright if locator is visible

Liang Wang — Fri, 16 Feb 2024 23:21:00 +0000

I have a project that sometimes will throw an error when try to delete an object.
I would like to catch that error and click on the OK button to close it.

Here is what works for me.

    const element = page.getByRole("button", { name: "OK" });
    if (await element.isVisible()) {
     await element.click();
    }