Using a debugger

How to:

Basic Debugging:

1. Setting Breakpoints:

To set a breakpoint, simply click on the left margin of the code line in your IDE (e.g., Visual Studio Code or Android Studio) where you want the execution to pause.

void main() {
  var message = 'Hello, Debugging';
  print(message); // Set a breakpoint here

2. Start Debugging:

In your IDE, initiate a debugging session by clicking on the debug icon or pressing the debug button. Execution will pause at breakpoints.

3. Inspect Variables:

Once execution is paused, hover over variables to see their current values.

4. Stepping Through Code:

Use the step over, step into, and step out commands in your IDE to navigate through your code one line or function at a time.

Advanced Debugging with Observatory:

Dart includes a tool called Observatory for debugging and profiling Dart applications. It’s particularly useful for applications running on the Dart VM.

Accessing Observatory:

Run your Dart application with the --observe flag.

dart --observe your_program.dart

This command prints a URL to the console, which you can open in a web browser to access the Observatory debugger.

Using Popular Third-party Libraries:

For debugging Flutter applications, the flutter_devtools package provides a suite of performance and debugging tools that integrate with both the Dart VM and Flutter.


First, add devtools to your pubspec.yaml file under dev_dependencies:

  devtools: any

Launching DevTools:

Run this command in your terminal:

flutter pub global run devtools

Then, start your Flutter application in debug mode. DevTools provides features such as the Flutter inspector for widget tree analysis, and the network profiler for monitoring network activity.

Sample Output:

Upon hitting a breakpoint, your IDE might display variable values and stack traces like so:

message: 'Hello, Debugging'

By effectively leveraging debugging tools and techniques in Dart, developers can identify and solve issues more rapidly, leading to a smoother development process and more robust applications.