////  ViewController.m//  01-加法计算器////  首先找main.m文件，然后找AppDelegate，然后找Main Inteferce主交互故事板，然后加载箭头指向的控制器，然后加载控制器内部的View。//  连线：按住control拖过去然后配置。//  类扩展：私有的属性和方法。      #import "ViewController.h"@interface ViewController ()@property (weak, nonatomic) IBOutlet UITextField *num1TextField;@property (weak, nonatomic) IBOutlet UITextField *num2TextField;@property (weak, nonatomic) IBOutlet UILabel *resultLabel;@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    self.num1TextField.placeholder = @"dddd";}- (IBAction)sum {    // 1. 拿到两个字符串    NSString *sum1String = self.num1TextField.text;    NSString *sum2String = self.num2TextField.text;        // 判断    if (sum1String.length == 0) {        /*        // 创建对象        UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"输入有误" message:@"请输入第一个数" delegate:nil cancelButtonTitle:@"我知道了" otherButtonTitles:nil, nil];                // 显示        [alertView show];        */        [self showInfo:@"请输入第一个数"];        return;    }        if (sum2String.length == 0) {        /*        // 创建对象        UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"输入有误" message:@"请输入第二个数" delegate:nil cancelButtonTitle:@"我知道了" otherButtonTitles:nil, nil];                // 显示        [alertView show];        */        [self showInfo:@"请输入第二个数"];        return;    }    // 2. 把字符串转成数值    NSInteger sum1 = [sum1String integerValue];    NSInteger sum2 = [sum2String integerValue];        // 3. 相加    NSInteger result = sum1 + sum2;        // 4. 显示结果    self.resultLabel.text = [NSString stringWithFormat:@"%zd", result];}//zd是无符号整型- (void)showInfo: (NSString *)info{    // 创建对象    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"输入有误" message:info delegate:nil cancelButtonTitle:@"我知道了" otherButtonTitles:nil, nil];        // 显示    [alertView show];}@end