This is a simple UITextFieldDelegate that allows easy formatting of localized currency or numerical inputs to string, whilst making it easy to still access the underlying value in the form of a Double.

To get started it's super simple.

1. Create an instance of the DoubleInputFormatterTextDelegate passing in your UITextField.

/// UITextField as required by component
lazy var bodyTextField: UITextField = {
    ...
}()

/// The formatter for our `UITextField`
lazy var textFieldFormatter: DoubleInputFormatterTextDelegate = {
    
    let textFieldFormatter = DoubleInputFormatterTextDelegate(
        field: bodyTextField
    )
    
    return textFieldFormatter
}()

2. Listen for changes to the underlying value

textFieldFormatter.valueForInput = { value in
    print("\(value)")
}

You can provide your own NumberFormatter and override the default currency one to have fine grained control over what's displayed.

A placeholder is only set when the UITextField's textAlignment property is set to .right. When set to .left the cursor sits in an odd location. Open to feedback on alternative approaches.

Pleas reference the demo app that shows how to use this simple class in your own projects.

Test's have been added to cover a myriad of use cases. Delegate and Target/Action pattern are not tested, but the internal logic of the transformation is.