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.