Add OnChange event handler to TextInput widget

widgets/textinput/editor.go

@@ -274,6 +274,9 @@ type fieldEditor struct {
 
 	// width is the width of the text input field last time viewFor was called.
 	width int
+
+	// onChange if provided is the handler called when fieldData changes
+	onChange ChangeFn
 }
 
 // newFieldEditor returns a new fieldEditor instance.
@@ -338,6 +341,9 @@ func (fe *fieldEditor) insert(r rune) {
 	}
 	fe.data.insertAt(fe.curDataPos, r)
 	fe.curDataPos++
+	if fe.onChange != nil {
+		fe.onChange(string(fe.data))
+	}
 }
 
 // delete deletes the rune at the current position of the cursor.
@@ -347,6 +353,9 @@ func (fe *fieldEditor) delete() {
 		return
 	}
 	fe.data.deleteAt(fe.curDataPos)
+	if fe.onChange != nil {
+		fe.onChange(string(fe.data))
+	}
 }
 
 // deleteBefore deletes the rune that is immediately to the left of the cursor.

widgets/textinput/options.go

@@ -63,6 +63,7 @@ type options struct {
 
 	filter                   FilterFn
 	onSubmit                 SubmitFn
+	onChange                 ChangeFn
 	clearOnSubmit            bool
 	exclusiveKeyboardOnFocus bool
 }
@@ -269,6 +270,19 @@ func OnSubmit(fn SubmitFn) Option {
 	})
 }
 
+// ChangeFn if provided is called when the content of the text input field changes,
+// the argument data contains all the text in the field.
+//
+// The callback function must be thread-safe as the keyboard event that
+// triggers the submission comes from a separate goroutine.
+type ChangeFn func(data string)
+
+func OnChange(fn ChangeFn) Option {
+	return option(func(opts *options) {
+		opts.onChange = fn
+	})
+}
+
 // ClearOnSubmit sets the text input to be cleared when a submit of the content
 // is triggered by the user pressing the Enter key.
 func ClearOnSubmit() Option {

widgets/textinput/textinput.go

@@ -73,7 +73,7 @@ func New(opts ...Option) (*TextInput, error) {
 		editor: newFieldEditor(),
 		opts:   opt,
 	}
-
+	ti.editor.onChange = opt.onChange
 	for _, r := range ti.opts.defaultText {
 		ti.editor.insert(r)
 	}