Using KVO to monitor the change of the control's properties (Observevalueforkeypath)

To create a test UIButton

#import "ViewController.h" @interface Viewcontroller () @property (nonatomic, strong) UIButton *button;@ End@implementation viewcontroller-(void) viewdidload {    [super viewdidload];        Self.button = [[UIButton alloc] Initwithframe:cgrectmake ((a);    [Self.button settitle:@ "test" forstate:uicontrolstatenormal];    [Self.button Settitlecolor:[uicolor Blackcolor] forstate:uicontrolstatenormal];    Self.button.layer.borderWidth = 1.0f;    [Self.view AddSubview:self.button];

Register the enabled state of the monitor button    [Self.button addobserver:self forkeypath:@ "enabled" options: Nskeyvalueobservingoptionnew context:@ "Test_button"];  Change the enabled state of the current button after 3 seconds    Dispatch_after (Dispatch_time (Dispatch_time_now, (int64_t) (3.0f * nsec_per_sec )), Dispatch_get_main_queue (), ^{        self.button.enabled = YES;    });

Adding listener observers

/** *  How to change the status of the monitor button * *  @param keypath button Changed properties *  @param object  button *  @param  Change the data after changes *  @ param Context Register monitoring when the context passes over the value */

-(void) Observevalueforkeypath: (NSString *) KeyPath Ofobject: (ID) object change: (nsdictionary *) Change context: (void *) Context {    UIButton *button = (UIButton *) object;    if (Self.button = = Button && [@ "Enabled" Isequaltostring:keypath]) {        NSLog (@ "Self.button's Enabled property changed%@", [Change objectforkey:@ "new"]);}    }

Using KVO to monitor the change of the control's properties (Observevalueforkeypath)