Programming Flex 3

Error Handling

ActionScript 3.0 supports runtime error handling. That means that if and when an error occurs, the application can respond to the error in an elegant fashion rather than simply failing to work without any notification to the user. ActionScript 3.0 uses two types of runtime errors: synchronous and asynchronous.

Handling Synchronous Errors

Synchronous errors occur immediately when trying to execute a statement. Use try/catch/finally to handle synchronous errors. When you have code that may throw runtime errors, surround it with a try statement:

try {
  // Code that might throw errors
}

You must then include one or more catch blocks following a try. If the code in the try block throws an error, the application attempts to match the error to the catch blocks in the order in which they appear. Every catch block must specify the specific type of error that it handles. The application runs the first catch block that it encounters to see whether it matches the type of error thrown. All error types are either flash.errors.Error types or subclasses of Error. Therefore, you should try to catch more specific error types first and more generic types (e.g., Error) later; for example:

try {
  // Code that might throw errors
}
catch (error:IOError) {
  // Code in case the specific error occurs
}
catch (error:Error) {
  // Code in case a non-specific error occurs
}

In addition, you can add a finally clause that runs regardless of whether the try statement is successful. A finally clause is used ...