Debugging Common Errors and Flatpak Issues

While building the Weather App, several errors may appear. These errors are normal and are part of the development process, especially when working with Rust, GTK, networking, threading, and Flatpak. Instead of memorizing solutions, it is more useful to understand why these errors occur. This section explains some common issues that beginners may encounter while developing or packaging the Weather App.

Common Application Errors - Window Appears Blank

Sometimes the application runs, but the window appears empty. This usually happens if the window is not presented or if no widget is attached to the window. In the Weather App, the window is displayed using:

#![allow(unused)]
fn main() {
window.present();
}

If this line is missing, the application runs but no window appears. Another possible issue is forgetting to attach the layout to the window:

#![allow(unused)]
fn main() {
window.set_content(Some(&layout));
}

If the content is not set correctly, the window will appear but it will be empty. A beginner should always check that:

• the window is presented
• the window has a valid content widget

UI Freezing During Weather Fetch

If the weather data is fetched directly on the main thread, the UI may freeze.

For example, this code would block the GTK UI thread:

#![allow(unused)]
fn main() {
let result = fetch_open_meteo(&query);
}

Network requests take time, and if they run on the UI thread, the interface cannot update.

In the Weather App, this is solved using a background thread:

#![allow(unused)]
fn main() {
thread::spawn(move || {
    let res = fetch_open_meteo(&query);
    let _ = tx.send(res);
});
}

This keeps the UI responsive while the weather data is fetched in the background.

If the UI freezes, the first thing to check is whether a long-running operation is blocking the main thread.

Resource or UI File Not Found

Another common error appears when GTK resources cannot be found.

For example, the program may show an error like:

The resource does not exist

This usually means the resource path does not match the configuration.

For example, if the resource prefix in resources.xml is:

<gresource prefix="/com/example/WeatherApp">

Then the UI file must be loaded using:

#![allow(unused)]
fn main() {
"/com/example/WeatherApp/weather.ui"
}

The path must match exactly. Even small differences can cause runtime errors.

Duplicate or Missing Cities

Sometimes the city list may show duplicates.

This usually happens if the CSV loading logic does not prevent duplicates.

In the Weather App, duplicates are avoided using:

#![allow(unused)]
fn main() {
!out.iter().any(|c| c.eq_ignore_ascii_case(city))
}

If this check is removed, the same city may appear multiple times.

When debugging data problems, it is helpful to check both:

• the in-memory city list
• the CSV file contents

Rust Borrowing Errors

Rust may produce compile errors related to borrowing and ownership. This can happen when using shared state like:

#![allow(unused)]
fn main() {
Rc<RefCell<Vec<String>>>
}

For example, mutation must be done carefully:

#![allow(unused)]
fn main() {
cities.borrow_mut().push(name);
}

If multiple mutable borrows occur at the same time, Rust will stop compilation. Although these errors may seem confusing at first, Rust usually provides very detailed error messages explaining the problem.

Flatpak Issues

Sometimes the Weather App works correctly with:

cargo run

but behaves differently when run inside Flatpak.

This happens because Flatpak runs the application inside a sandbox environment that restricts access to system resources.

Understanding these restrictions helps beginners debug Flatpak problems.

Network Requests Not Working

The Weather App fetches weather data using network requests such as:

#![allow(unused)]
fn main() {
reqwest::blocking::get(&weather_url)
}

If the Flatpak manifest does not include the permission:

- --share=network

the sandbox blocks internet access. The application will start normally, but the API request will fail. This is one of the most common Flatpak issues.

File Storage Not Working

The Weather App saves cities using a CSV file:

#![allow(unused)]
fn main() {
const CSV_FILE: &str = "saved_cities.csv";
}

and writes data using:

#![allow(unused)]
fn main() {
fs::write(CSV_FILE, buf);
}

Inside Flatpak, file access may fail if the filesystem permission is missing.

The manifest includes:

- --filesystem=home

Without this permission, the application cannot write to the home directory. This may confuse beginners because the same code works perfectly with cargo run.

Runtime Version Problems

Another issue can occur if the required runtime version is not installed.

For example, the manifest may specify:

runtime-version: '49'

If this runtime is not installed, Flatpak may show an error such as:

Requested extension not installed

The solution is to install the runtime manually:

flatpak install flathub org.gnome.Platform//49

Resource Files Missing in Flatpak

Sometimes the application works locally but fails inside Flatpak with resource errors.

For example:

#![allow(unused)]
fn main() {
gtk::Builder::from_resource("/com/example/WeatherApp/weather.ui");
}

If the UI file was not compiled correctly into the resource bundle, Flatpak will not find it.

Flatpak builds the project in an isolated environment, so files must be included using compiled resources instead of relative file paths.

Application Window Appears but UI Is Incomplete

If the application window opens but some widgets are missing, the issue may be related to the runtime environment.

Flatpak runs the application using the runtime defined in the manifest:

runtime: org.gnome.Platform

If the application requires a GTK or Libadwaita feature that is not available in that runtime version, the UI may behave incorrectly. Ensuring that the runtime version matches the application requirements helps prevent this issue.

Why Debugging Is Important

Debugging is an important part of learning software development. The Weather App combines several technologies:

• Rust programming
• GTK user interface
• networking
• threading
• file storage
• Flatpak sandbox packaging

Each of these layers can introduce errors.

By understanding how these components work together, beginners can learn how to identify and fix problems more effectively. Errors are not failures. They are opportunities to understand the system more deeply and improve development skills.