Debugging with Breakpoints

Debugging with Breakpoints

About

• Breakpoints pause code execution for inspection.
• Supported in IDEs (VSCode, Android Studio) and DevTools.
• Allows examining variables, call stack, and control flow.
• Essential for diagnosing runtime issues.

Main Topics

1. Setting Breakpoints

   • Definition: How to add breakpoints in IDEs.
   • Example:

     void calculate() {
       int x = 5; // Set breakpoint on this line
       print(x * 2);
     }

2. Breakpoint Types

   • Definition: Line vs conditional vs exception breakpoints.
   • Example:

     // Conditional breakpoint (VSCode):
     // Right-click → Add Conditional Breakpoint
     // Condition: `x > 10`

3. Execution Control

   • Definition: Step Over/Into/Out commands.
   • Example:

     void main() {
       print('Start'); // Step Over
       calculate();    // Step Into
     }

4. Inspecting State

   • Definition: Viewing variables and call stack.
   • Example:

     // During breakpoint pause:
     // - Hover variables for values
     // - View Call Stack panel

5. Logging Breakpoints

   • Definition: Breakpoints that log without pausing.
   • Example:

     // In VSCode:
     // Right-click → Add Logpoint
     // Message: 'x value: {x}'

How to Use

• Set: Click gutter in IDE or use debugger() statement
• Manage: Enable/disable in “Breakpoints” view
• Navigate: F8 (Step Over), F7 (Step Into) in VSCode
• Inspect: Watch expressions for complex variables

How It Works

• Compilation: Debug info embedded in Dart bytecode
• Pausing: VM suspends at breakpoint locations
• State Capture: Snapshots variable values when paused
• Resume: VM continues execution on command

Example Debug Session:

void main() {
  debugger(); // Programmatic breakpoint
  for (var i = 0; i < 5; i++) {
    print(i); // Set line breakpoint here
  }
}

Conclusion

Dart DevTools is an indispensable suite for debugging and optimizing Dart applications. It provides real-time insights into app performance, memory usage, and widget hierarchies, making it essential for developing production-quality applications with efficient data handling and smooth execution.