问题
How can I detect any text changes in a textField? The delegate method shouldChangeCharactersInRange works for something, but it did not fulfill my need exactly. Since until it returns YES, the textField texts are not available to other observer methods.
e.g. in my code calculateAndUpdateTextFields did not get the updated text, the user has typed.
Is their any way to get something like textChanged Java event handler.
- (BOOL)textField:(UITextField *)textField
shouldChangeCharactersInRange:(NSRange)range
replacementString:(NSString *)string
{
if (textField.tag == kTextFieldTagSubtotal
|| textField.tag == kTextFieldTagSubtotalDecimal
|| textField.tag == kTextFieldTagShipping
|| textField.tag == kTextFieldTagShippingDecimal)
{
[self calculateAndUpdateTextFields];
}
return YES;
}
回答1:
From proper way to do uitextfield text change call back:
I catch the characters sent to a UITextField control something like this:
// Add a "textFieldDidChange" notification method to the text field control.
In Objective-C:
[textField addTarget:self
action:@selector(textFieldDidChange:)
forControlEvents:UIControlEventEditingChanged];
In Swift:
textField.addTarget(self, action: #selector(textFieldDidChange), for: .editingChanged)
Then in the
textFieldDidChangemethod you can examine the contents of the textField, and reload your table view as needed.
You could use that and put calculateAndUpdateTextFields as your selector.
回答2:
XenElement's answer is spot on.
The above can be done in interface builder too by right-clicking on the UITextField and dragging the "Editing Changed" send event to your subclass unit.
回答3:
to set the event listener:
[self.textField addTarget:self action:@selector(textFieldDidChange:) forControlEvents:UIControlEventEditingChanged];
to actually listen:
- (void)textFieldDidChange:(UITextField *)textField {
NSLog(@"text changed: %@", textField.text);
}
回答4:
Swift:
yourTextfield.addTarget(self, action: #selector(textFieldDidChange(textField:)), for: .editingChanged)
Then, implement the callback function:
@objc func textFieldDidChange(textField: UITextField){
print("Text changed")
}
回答5:
As stated here: UITextField text change event, it seems that as of iOS 6 (iOS 6.0 and 6.1 checked) it is not possible to fully detect changes in UITextField objects just by observing the UITextFieldTextDidChangeNotification.
It seems that only those changes made directly by the built-in iOS keyboard are tracked now. This means that if you change your UITextField object just by invoking something like this: myUITextField.text = @"any_text", you won't be notified about any changes at all.
I don't know if this is a bug or it is intended. Seems like a bug since I haven't found any reasonable explanation in documentation. This is also stated here: UITextField text change event.
My "solution" to this is to actually post a notification by myself for every change I make to my UITextField (if that change is done without using the built-in iOS keyboard). Something like this:
myUITextField.text = @"I'm_updating_my_UITextField_directly_in_code";
NSNotification *myTextFieldUpdateNotification =
[NSNotification notificationWithName:UITextFieldTextDidChangeNotification
object:myUITextField];
[NSNotificationCenter.defaultCenter
postNotification:myTextFieldUpdateNotification];
This way you are 100% confident that you'll receive the same notification when you change the .text property of your UITextField object, either when you update it "manually" in your code or through the built-in iOS keyboard.
It is important to consider that, since this is not a documented behavior, this approach may lead to 2 notifications received for the same change in your UITextField object. Depending on your needs (what you actually do when your UITextField.text changes) this could be an inconvenience for you.
A slightly different approach would be to post a custom notification (this is, with a custom name other than UITextFieldTextDidChangeNotification) if you actually need to know whether the notification was yours or "iOS-made".
EDIT:
I've just found a different approach which I think could be better:
This involves the Key-Value Observing (KVO) feature of Objective-C (http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/KeyValueObserving/KeyValueObserving.html#//apple_ref/doc/uid/10000177-BCICJDHA).
Basically, you register yourself as an observer of a property and if this property changes you get notified about it. The "principle" is quite similar to how NSNotificationCenter works, being the main advantage that this approach works automatically also as of iOS 6 (without any special tweak like having to manually post notifications).
For our UITextField-scenario this works just fine if you add this code to, for example, your UIViewController that contains the text field:
static void *myContext = &myContext;
- (void)viewDidLoad {
[super viewDidLoad];
//Observing changes to myUITextField.text:
[myUITextField addObserver:self forKeyPath:@"text"
options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld
context:myContext];
}
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
change:(NSDictionary *)change context:(void *)context {
if(context == myContext) {
//Here you get notified every time myUITextField's "text" property is updated
NSLog(@"New value: %@ - Old value: %@",
[change objectForKey:NSKeyValueChangeNewKey],
[change objectForKey:NSKeyValueChangeOldKey]);
}
else
[super observeValueForKeyPath:keyPath ofObject:object
change:change context:context];
}
Credit to this answer regarding "context" management: https://stackoverflow.com/a/12097161/2078512
Note: Seems like while you are in the process of editing a UITextField with the built-in iOS keyboard, the "text" property of the text field is not updated with every new letter typed/removed. Instead, the text field object gets updated "as a whole" after you resign the first responder status of the text field.
回答6:
We can easily configure that from Storyboard, CTRL drag the @IBAction and change event as following:
回答7:
Here in swift version for same.
textField.addTarget(self, action: "textFieldDidChange:", forControlEvents: UIControlEvents.EditingChanged)
func textFieldDidChange(textField: UITextField) {
}
Thanks
回答8:
I resolved the issue changing the behavior of shouldChangeChractersInRange. If you return NO the changes won't be applied by iOS internally, instead you have the opportunity to change it manually and perform any actions after the changes.
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
//Replace the string manually in the textbox
textField.text = [textField.text stringByReplacingCharactersInRange:range withString:string];
//perform any logic here now that you are sure the textbox text has changed
[self didChangeTextInTextField:textField];
return NO; //this make iOS not to perform any action
}
回答9:
Swift Version tested:
//Somewhere in your UIViewController, like viewDidLoad(){ ... }
self.textField.addTarget(
self,
action: #selector(SearchViewController.textFieldDidChange(_:)),
forControlEvents: UIControlEvents.EditingChanged
)
Parameters explained:
self.textField //-> A UITextField defined somewhere in your UIViewController
self //-> UIViewController
.textFieldDidChange(_:) //-> Can be named anyway you like, as long as it is defined in your UIViewController
Then add the method you created above in your UIViewController:
//Gets called everytime the text changes in the textfield.
func textFieldDidChange(textField: UITextField){
print("Text changed: " + textField.text!)
}
回答10:
Swift 4
func addNotificationObservers() {
NotificationCenter.default.addObserver(self, selector: #selector(textFieldDidChangeAction(_:)), name: .UITextFieldTextDidChange, object: nil)
}
@objc func textFieldDidChangeAction(_ notification: NSNotification) {
let textField = notification.object as! UITextField
print(textField.text!)
}
回答11:
For Swift 3.0:
let textField = UITextField()
textField.addTarget(
nil,
action: #selector(MyClass.textChanged(_:)),
for: UIControlEvents.editingChanged
)
using class like:
class MyClass {
func textChanged(sender: Any!) {
}
}
回答12:
Swift 3 Version
yourTextField.addTarget(self, action: #selector(YourControllerName.textChanges(_:)), for: UIControlEvents.editingChanged)
And get the changes in here
func textChanges(_ textField: UITextField) {
let text = textField.text! // your desired text here
// Now do whatever you want.
}
Hope it helps.
回答13:
You should use the notification to solve this problem,because the other method will listen to the input box not the actually input,especially when you use the Chinese input method. In viewDidload
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textFiledEditChanged:)
name:@"UITextFieldTextDidChangeNotification"
object:youTarget];
then
- (void)textFiledEditChanged:(NSNotification *)obj {
UITextField *textField = (UITextField *)obj.object;
NSString *toBestring = textField.text;
NSArray *currentar = [UITextInputMode activeInputModes];
UITextInputMode *currentMode = [currentar firstObject];
if ([currentMode.primaryLanguage isEqualToString:@"zh-Hans"]) {
UITextRange *selectedRange = [textField markedTextRange];
UITextPosition *position = [textField positionFromPosition:selectedRange.start offset:0];
if (!position) {
if (toBestring.length > kMaxLength)
textField.text = toBestring;
}
}
finally,you run,will done.
回答14:
Swift 3.1:
Selector: ClassName.MethodName
cell.lblItem.addTarget(self, action: #selector(NewListScreen.fieldChanged(textfieldChange:)), for: .editingChanged)
func fieldChanged(textfieldChange: UITextField){
}
回答15:
Swift 3 Version:
class SomeClass: UIViewController, UITextFieldDelegate {
@IBOutlet weak var aTextField: UITextField!
override func viewDidLoad() {
super.viewDidLoad()
aTextField.delegate = self
aTextField.addTarget(self, action: #selector(SignUpVC.textFieldDidChange), for: UIControlEvents.editingChanged)
}
func textFieldDidChange(_ textField: UITextField) {
//TEXT FIELD CHANGED..SECRET STUFF
}
}
Don't forget to set the delegate.
回答16:
With closure:
class TextFieldWithClosure: UITextField {
var targetAction: (() -> Void)? {
didSet {
self.addTarget(self, action: #selector(self.targetSelector), for: .editingChanged)
}
}
func targetSelector() {
self.targetAction?()
}
}
and using
textField.targetAction? = {
// will fire on text changed
}
回答17:
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(didChangeTextViewText:)
name:UITextFieldTextDidChangeNotification object:nil];
- (void) didChangeTextViewText {
//do something
}
回答18:
Swift 4 Version
Using Key-Value Observing Notify objects about changes to the properties of other objects.
var textFieldObserver: NSKeyValueObservation?
textFieldObserver = yourTextField.observe(\.text, options: [.new, .old]) { [weak self] (object, changeValue) in
guard let strongSelf = self else { return }
print(changeValue)
}
来源：https://stackoverflow.com/questions/7010547/uitextfield-text-change-event