Value vs. Reference: How Does C# Pass Objects to Methods?

C# method parameter transfer: value type and reference type

In C#, the behavior of non -original type variables has been widely accepted by reference. However, some developers may encounter differences when dealing with objects such as System.Drawing.image. Understanding the details of the object transmission are essential for avoiding accidents.

By default, the object is not directly passed to the method. Instead, the corresponding values ​​are evaluated and the initial parameter values ​​are passed as parameters. For the reference type (non -original type), this value represents the reference to the actual object or NULL. Therefore, any modification of the object inside the method can be visible to the caller.

However, it is important to note that the value of the parameter is changed to another different object. When the use value is passed (default), it will not be reflected in the scope of the callor.

To transmit the semantics according to reference, the

or

keywords must be used, regardless of what the parameter type is. By specifying these keywords, the parameters themselves will be passed according to reference to ensure that the changes to the parameters can be seen. out ref The following is a simplified example:

On the contrary, the modification of the data in the reference object when passing the object will be visible to the caller.

<code class="language-csharp">public void Foo(Image image) // 按值传递
{
    // 对参数的更改对调用者不可见。
    image = Image.FromStream(...);
}

public void Foo(ref Image image) // 按引用传递
{
    // 对参数的更改对调用者可见。
    image = Image.FromStream(...);
}</code>

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