xcode简单教程，实现一个button点击事件

1.新建工程

File->New->Project->SingleViewApplication->Next->ProductName->Next

2.ViewController添加按钮

viewDidLoad 方法添加：

[self setupUI];

实现setupUI：

#pragma mark - Setup- (void)setupUI {    // Hello button.    UIButton *helloButton = [UIButton buttonWithType:UIButtonTypeSystem];    [helloButton setTitle:@"Hello" forState:UIControlStateNormal];    [helloButton addTarget:self action:@selector(onHelloButtonClicked:) forControlEvents:UIControlEventTouchUpInside];    [self.view addSubview:helloButton];    //// Layout with frame.    //[helloButton setFrame:CGRectMake(0, 0, 60, 40)];    //helloButton.center = self.view.center;    //// Layout with constraint.    helloButton.translatesAutoresizingMaskIntoConstraints = NO; // If you want to use Auto Layout to dynamically calculate the size and position of your view, you must set this property to NO.    [self.view addConstraints:@[                                [NSLayoutConstraint constraintWithItem:helloButton attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:60.0],                                [NSLayoutConstraint constraintWithItem:helloButton attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:40.0],                                [NSLayoutConstraint constraintWithItem:helloButton attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0],                                [NSLayoutConstraint constraintWithItem:helloButton attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0]                                ]];}

实现点击事件：

#pragma mark - Action- (void)onHelloButtonClicked:(id)sender {    NSLog(@"Hello, world!");    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"Hello" message:@"Hello, world!" preferredStyle:UIAlertControllerStyleAlert];    UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {        NSLog(@"Cancle Action");    }];    UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {        NSLog(@"OK Action");    }];    [alertController addAction:cancelAction];    [alertController addAction:okAction];    [self presentViewController:alertController animated:YES completion:nil];}