通过Swift学习Objective-C：条件、流程、集合

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上一篇教程简单通过Swift学习Objective-C：变量、类、方法和属性学习了变量、类、方法和属性。这一篇了解Objective-C中的条件，流程和集合的表达方式。

这篇教程适合已学习Swift，至少写个一个demo，想了解一下Objective-C语法的同学们。

控制流程（Control Flow）

IF条件

Swift

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var score = 25
if score > 25 {

}

var aString: String?
if let myString = aString {
}

Swift中用？表示一个变量可以为空值，而if let myString = aString仅在aString存在，及不为空值时候才能运行

Objective-C

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int score = 25;
if (score < 25) {

  }

NSString *aString;
if (aString) {
}

Switch选择

Swift

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var numberOfPeople = 1

switch numberOfPeople {
    case 1:
        // code for this case
    case 2:
        // code for this case
    default:
        // code for this case
}

Objective-C

Objective-C中每一个Case需要以Break; 结尾

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int numberOfPeople = 1;

switch (numberOfPeople)
{
    case 1:
        // code for this case
        break;
    case 2:
        // code for this case
        break;
    default:
        // code for this case
        break;
}

循环

For循环

Swift

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or var i = 0; i < 10; i++ {
}

for i in 0..10 {
}

var array = ["item 1", "item 2"]
for item in array {
}

Objective-C

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for (int i = 0; i < 10; i++) {
}

NSArray *array = @[@"item 1", @"item 2"];
for (NSString *item in array) {
}

While循环

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var count = 1
while count < 10 {
    count++
}

do
{
    count++
} while count < 10

Objective-C

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int count = 1;
while (count < 10) {
    count++;
}

do
{
    count++;
} while (count &lt; 10);

集合

声明一个数组

Swift

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var myArray:[String] = [String]()
var myArray2 = ["item 1", "item 2"]

Objective-C

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NSMutableArray *myArray = [[NSMutableArray alloc] init];//创建并初始化
NSMutableArray *myArray2 = [@[@"item 1", @"item 2"] mutableCopy];//直接赋值

向数组添加元素

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myArray[0] = "item 1"

myArray.append("item 3")
myArray += "item 3"

myArray.insert("item 4", atIndex:1)

Objective-C

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myArray[0] = @"item 1";

[myArray addObject:@"item 3"];

[myArray insertObject:@"item 4" atIndex:1];

声明一个词典（Dictionary）

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var myDictionary = Dictionary&lt;String, String&gt;()

var myDictionary2 = ["key":"object", "key2":"object 2"]

Objective-C

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NSMutableDictionary *myDictionary = [[NSMutableDictionary alloc] init];

NSMutableDictionary *myDictionary2 = [@{@"key":@"object", @"key2":@"object 2"} mutableCopy];

添加/修改词典元素

Swift

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myDictionary["key3"] = "object 3"
myDictionary["key2"] = "object 4"

Objective-C

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[myDictionary setObject:@"object 3" forKey:@"key3"];
myDictionary[@"key2"] = @"object 4";

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参考