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

[self 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]
]];
}

#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];
}