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];
}