throw
Type
control structure
Summary
Returns an error message to a control structure.
Syntax
throw <errorString>
Description
Use the throw control structure in a handler called from within a try control structure.
Form: The throw statement appears on a line by itself, anywhere inside a handler.
If LiveCode generates the error (for example, an execution error from a built-in command), it returns a positive number to the try control structure. To avoid confusion, therefore, a throw control structure should return a negative number, or a non-numeric string.
If a throw control structure is executed in a handler that was not called from within a try control structure, an errorDialog message is sent to the object, and the errorString is passed as a parameter.
The throw control structure is implemented internally as a command and appears in the commandNames.
Parameters
| Name | Type | Description |
|---|---|---|
errorString | string | The string that is returned to the calling try control structure. The errorString becomes the parameter of the catch line in the try control structure. |
Examples
open file tFile for text read
if the result is not empty then
throw "failed_to_open_file"
end if
Related
message: errorDialog
control structure: return, try
function: commandNames
glossary: return, call, handler, execute, statement, message, negative, control structure, parameter, command, object
Compatibility and Support
Introduced
LiveCode 1.0
OS
mac
windows
linux
ios
android
Platforms
desktop
server
mobile