Question

我知道装箱转换值类型为对象和拆箱将对象转换为值类型。例如：

int num = 1;
Object obj = num;      //boxing
int num2 = (int)obj    //unboxing

但是当我在现实生活中使用它时（当我写一些代码时）？我从不将Int分配给Object（或者我认为是这样，我没有明确地写它）

Answer 1

拳击/取消装箱对于你可能拥有一系列不同的东西，其中一些是基元而另一些是对象类型的情况很有用，例如List<object>。实际上，如果您搜索＆＃34; msdn拳击，那么他们在Boxing and Unboxing文档页面中提供的示例：＆＃34;

// List example. 
// Create a list of objects to hold a heterogeneous collection  
// of elements.
List<object> mixedList = new List<object>();

// Add a string element to the list. 
mixedList.Add("First Group:");

// Add some integers to the list.  
for (int j = 1; j < 5; j++)
{
    // Rest the mouse pointer over j to verify that you are adding 
    // an int to a list of objects. Each element j is boxed when  
    // you add j to mixedList.
    mixedList.Add(j);
}

// Add another string and more integers.
mixedList.Add("Second Group:");
for (int j = 5; j < 10; j++)
{
    mixedList.Add(j);
}

// Display the elements in the list. Declare the loop variable by  
// using var, so that the compiler assigns its type. 
foreach (var item in mixedList)
{
    // Rest the mouse pointer over item to verify that the elements 
    // of mixedList are objects.
    Console.WriteLine(item);
}

// The following loop sums the squares of the first group of boxed 
// integers in mixedList. The list elements are objects, and cannot 
// be multiplied or added to the sum until they are unboxed. The 
// unboxing must be done explicitly. 
var sum = 0;
for (var j = 1; j < 5; j++)
{
    // The following statement causes a compiler error: Operator  
    // '*' cannot be applied to operands of type 'object' and 
    // 'object'.  
    //sum += mixedList[j] * mixedList[j]); 

    // After the list elements are unboxed, the computation does  
    // not cause a compiler error.
    sum += (int)mixedList[j] * (int)mixedList[j];
}

// The sum displayed is 30, the sum of 1 + 4 + 9 + 16.
Console.WriteLine("Sum: " + sum);

// Output: 
// Answer42True 
// First Group: 
// 1 
// 2 
// 3 
// 4 
// Second Group: 
// 5 
// 6 
// 7 
// 8 
// 9 
// Sum: 30

我什么时候使用拳击和拆箱？

1 个答案: