Objective-C 常用類別實戰速查：委派、通知、字串、陣列、字典、檔案枚舉

編輯：關於C語言

1. 委派模式


// A.h
@protocol ViewControllerADelegate 
- (void)changeBgColorFromCtrlA:(ViewControllerA*)aView withColor:(UIColor*)color;
@end
@interface ViewControllerA : UIViewController
@property (nonatomic, weak) id delegate;
- (IBAction)changeColorAction:(id)sender;
@end

// A.m
- (IBAction)changeColorAction:(id)sender {
    [self.delegate changeBgColorFromCtrlA:self withColor:[UIColor grayColor]];
    [self.navigationController popViewControllerAnimated:YES];
}

// B.m 實作協議
- (void)changeBgColorFromCtrlA:(ViewControllerA*)aView withColor:(UIColor*)color {
    self.view.backgroundColor = color;
}

2. 通知中心


// A.m 發送
[[NSNotificationCenter defaultCenter] postNotificationName:@"ChangeColorKey"
                                                    object:[UIColor greenColor]];

// B.m 註冊與接收
- (void)viewDidLoad {
    [super viewDidLoad];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(changeColor:)
                                                 name:@"ChangeColorKey"
                                               object:nil];
}
- (void)changeColor:(NSNotification*)note {
    if (note.object) self.view.backgroundColor = note.object;
}
- (void)dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

3. NSString 常用操作

操作	方法	範例
建立	`stringWithFormat:`	`NSString *s = [NSString stringWithFormat:@"%@%@", a, b];`
比較	`isEqualToString:`	`[a isEqualToString:b]`
前綴/後綴	`hasPrefix:` / `hasSuffix:`	`[a hasPrefix:@"https://"]`
忽略大小寫	`caseInsensitiveCompare:`	`[a caseInsensitiveCompare:b] == NSOrderedSame`
分割	`componentsSeparatedByString:`	`[@"a,b,c" componentsSeparatedByString:@","] → @[@"a",@"b",@"c"]`
合併陣列	`componentsJoinedByString:`	`[@[@"a",@"b"] componentsJoinedByString:@","] → @"a,b"`
大小寫轉換	`uppercaseString` / `lowercaseString`
子字串	`substringToIndex:` `substringFromIndex:` `substringWithRange:`	`[s substringWithRange:NSMakeRange(0,4)]`
路徑副檔名	`pathExtension`	`[@"file.txt" pathExtension] → @"txt"`
檔案讀寫	`initWithContentsOfFile:` `writeToFile:atomically:`

4. NSArray / NSMutableArray


// 建立
NSArray *arr = @[@"a", @"b", @"c"]; // 字面值語法
NSMutableArray *mar = [NSMutableArray arrayWithArray:arr];

// 快速枚舉 (推薦)
for (id obj in mar) { ... }

// 列舉器 (反向)
NSEnumerator *e = [mar reverseObjectEnumerator];
while (id obj = [e nextObject]) { ... }

// 複製 (深複製需元素支援 NSCopying)
NSMutableArray *copy = [NSMutableArray arrayWithArray:mar];

// 排序
[mar sortUsingSelector:@selector(compare:)];
// 自訂比較
[mar sortUsingComparator:^NSComparisonResult(id a, id b) { return [a compare:b]; }];

5. NSDictionary / NSMutableDictionary


NSDictionary *dict = @{@"key1": @"val1", @"key2": @"val2"};
NSString *v = dict[@"key1"]; // 現代語法
[mutableDict setObject:@"new" forKey:@"key1"];
[mutableDict removeObjectForKey:@"key2"];

6. 檔案目錄枚舉


NSFileManager *fm = [NSFileManager defaultManager];
NSString *home = @"/Users"; // 或 NSHomeDirectory()
NSDirectoryEnumerator *dirEnum = [fm enumeratorAtPath:home];
NSMutableArray *jpgFiles = [NSMutableArray array];

for (NSString *fname in dirEnum) {
    if ([[fname pathExtension] isEqualToString:@"jpg"])
        [jpgFiles addObject:fname];
}
// 或舊式 while 迴圈
while (NSString *fname = [dirEnum nextObject]) { ... }