iOS 數組學習

1.創建數組

// 創建一個空的數組
NSArray *array = [NSArray array];
// 創建有1個元素的數組
array = [NSArray arrayWithObject:@"123"];
// 創建有多個元素的數組
array = [NSArray arrayWithObjects:@"a", @"b", @"c", nil nil];
NSArray *array3 = [array arrayByAddingObjectsFromArray:[NSArray arrayWithObjects:@"4", @"5", nil nil]];

NSArray *array4 = [NSArray arrayWithObjects:@"1", @"2", @"3", @"4", nil nil];
NSRange range = NSMakeRange(1, 2);
NSArray *array5 = [array4 subarrayWithRange:range];

2.數組的一些基本方法

int count = [array count];//個數
// 判斷是否包含了某個元素
if ([array containsObject:@"a"]) {
    NSLog(@"包含了字符串a");
}
NSString *last = [array lastObject];最後一個元素
NSString *str = [array objectAtIndex:1];根據索引獲取數組中的元素
int index = [array indexOfObject:@"c"];獲取指定元素的索引
// 讓數組裏面的所有對象都調用test方法，123爲參數
NSArray *array = [NSArray arrayWithObjects:stu1, stu2, stu3, nil nil];
[array makeObjectsPerformSelector:@selector(test2:) withObject:@"123"];
NSArray *array = [NSArray arrayWithObjects:@"1", @"2", @"3", @"4", nil nil];
// 1-2-3-4
// 利用分隔符-拼接所有的數組元素
NSString *str = [array componentsJoinedByString:@"-"];
// 將一個數組寫入文件（生成的是一個xml文件）
NSString *path = @"/Users/apple/Desktop/array.xml";
[array writeToFile:path atomically:YES];
path = @"/Users/apple/Desktop/array.txt";
// 從文件中讀取數組內容（文件有嚴格的格式要求）
NSArray *array2 = [NSArray arrayWithContentsOfFile:path];

3.遍歷數組

#pragma mark 遍歷數組1
void arrayFor1() {
    NSArray *array = [NSArray arrayWithObjects:stu1, @"1", @"2", @"3", nil nil];
    int count = array.count;
    for (int i = 0; i<count; i++) {
        id obj = [array objectAtIndex:i];
    }
}

#pragma mark 遍歷數組2 快速遍歷
void arrayFor2() {
    Student *stu1 = [Student student];
    NSArray *array = [NSArray arrayWithObjects:stu1, @"1", @"2", @"3", nil nil];
    int i =0;
    for (id obj in array) {
        NSLog(@"%i-%@", i, obj);
        i++;
    }
}

#pragma mark 遍歷數組3
void arrayFor3() {
    Student *stu1 = [Student student];
    NSArray *array = [NSArray arrayWithObjects:stu1, @"1", @"2", @"3", nil nil];
    [array enumerateObjectsUsingBlock:
     ^(id obj, NSUInteger idx, BOOLBOOL *stop) {
        NSLog(@"%i-%@", idx, obj);
         // 如果索引爲1，就停止遍歷
         if (idx == 1) {
             // 利用指針修改外面BOOL變量的值
             *stop = YES;
         }
    }];
}

#pragma mark 遍歷數組4
void arrayFor4() {
    Student *stu1 = [Student student];
    NSArray *array = [NSArray arrayWithObjects:stu1, @"1", @"2", @"3", nil nil];
    // 獲取數組的迭代器
    // NSEnumerator *enumerator = [array objectEnumerator];
    // 反序迭代器（從尾部開始遍歷元素）
    NSEnumerator *enumerator = [array reverseObjectEnumerator];
    // allObjects是取出沒有被遍歷過的對象
    NSArray *array2 = [enumerator allObjects];
    NSLog(@"array2:%@", array2);
    // 獲取下一個需要遍歷的元素
    id obj = nil;
    while (obj = [enumerator nextObject]) {
        NSLog(@"obj=%@", obj);
    }
}

4.數組排序

#pragma mark 數組排序1
void arraySort1() {
    NSArray *array = [NSArray arrayWithObjects:@"2", @"3", @"1", @"4", nil nil];

    // 返回一個排好序的數組，原來數組的元素順序不會改變
    // 指定元素的比較方法：compare:
    NSArray *array2 = [array sortedArrayUsingSelector:@selector(compare:)];
    NSLog(@"array2:%@", array2);
}

#pragma mark 數組排序2
void arraySort2() {
    Student *stu1 = [Student studentWithFirstname:@"MingJie" lastname:@"Li"];
    Student *stu2 = [Student studentWithFirstname:@"LongHu" lastname:@"Huang"];
    Student *stu3 = [Student studentWithFirstname:@"LianJie" lastname:@"Li"];
    Student *stu4 = [Student studentWithFirstname:@"Jian" lastname:@"Xiao"];
    NSArray *array = [NSArray arrayWithObjects:stu1,stu2,stu3, stu4, nil nil];
    // 指定排序的比較方法
    NSArray *array2 = [array sortedArrayUsingSelector:@selector(compareStudent:)];
    NSLog(@"array2:%@", array2);
}
- (NSComparisonResult)compareStudent:(Student *)stu {
    // 先按照姓排序
    NSComparisonResult result = [self.lastname compare:stu.lastname];
    // 如果有相同的姓，就比較名字
    if (result == NSOrderedSame) {
        result = [self.firstname compare:stu.firstname];
    }
    return result;
}

#pragma mark 數組排序3
void arraySort3() {
    Student *stu1 = [Student studentWithFirstname:@"MingJie" lastname:@"Li"];
    Student *stu2 = [Student studentWithFirstname:@"LongHu" lastname:@"Huang"];
    Student *stu3 = [Student studentWithFirstname:@"LianJie" lastname:@"Li"];
    Student *stu4 = [Student studentWithFirstname:@"Jian" lastname:@"Xiao"];
    NSArray *array = [NSArray arrayWithObjects:stu1,stu2,stu3, stu4, nil nil];

    // 利用block進行排序
    NSArray *array2 = [array sortedArrayUsingComparator:
     ^NSComparisonResult(Student *obj1, Student *obj2) {
         // 先按照姓排序
         NSComparisonResult result = [obj1.lastname compare:obj2.lastname];
         // 如果有相同的姓，就比較名字
         if (result == NSOrderedSame) {
             result = [obj1.firstname compare:obj2.firstname];
         }

         return result;
    }];

    NSLog(@"array2:%@", array2);
}

#pragma mark 數組排序4-高級排序
void arraySort4() {
    Student *stu1 = [Student studentWithFirstname:@"MingJie" lastname:@"Li" bookName:@"book1"];
    Student *stu2 = [Student studentWithFirstname:@"LongHu" lastname:@"Huang" bookName:@"book2"];
    Student *stu3 = [Student studentWithFirstname:@"LianJie" lastname:@"Li" bookName:@"book2"];
    Student *stu4 = [Student studentWithFirstname:@"Jian" lastname:@"Xiao" bookName:@"book1"];
    NSArray *array = [NSArray arrayWithObjects:stu1,stu2,stu3, stu4, nil nil];

    // 1.先按照書名進行排序
    // 這裏的key寫的是@property的名稱
    NSSortDescriptor *bookNameDesc = [NSSortDescriptor sortDescriptorWithKey:@"book.name" ascending:YES];
    // 2.再按照姓進行排序
    NSSortDescriptor *lastnameDesc = [NSSortDescriptor sortDescriptorWithKey:@"lastname" ascending:YES];
    // 3.再按照名進行排序
    NSSortDescriptor *firstnameDesc = [NSSortDescriptor sortDescriptorWithKey:@"firstname" ascending:YES];
    // 按順序添加排序描述器
    NSArray *descs = [NSArray arrayWithObjects:bookNameDesc, lastnameDesc, firstnameDesc, nil nil];

    NSArray *array2 = [array sortedArrayUsingDescriptors:descs];

    NSLog(@"array2:%@", array2);
}