C＃中的KeyLogger问题

Question

I want to log my keyboard strokes. However, when I add a new keyboard to keyList, it changes all items to the new one. For example, if keyList contains A and B, and I type C, then my keyList would C, C ,C instead of A,B,C.

do you know what causing this problem? Shouldn't I use List ?

KeyboardEvent myKeyBoardEvent = new KeyboardEvent();
List<KeyboardEvent> keyList = new List<KeyboardEvent>();
List<WorkflowEvent> myLogs = new List<WorkflowEvent>();

public void LogKeyboadEvent(Key keyboard)
{
myKeyBoardEvent.Key = keyboard.ToString();
keyList.Add(myKeyBoardEvent);
myLogs.Add(myKeyBoardEvent);
}

Answer 1

KeyboardEvent is a class, and therefore passed "by reference". This means that you only ever have one copy of it. You are adding the same object to the list 3 times.

This would also have the same effect:

myKeyBoardEvent.Key = "A";
myLogs.Add(myKeyBoardEvent);
myLogs.Add(myKeyBoardEvent);
myLogs.Add(myKeyBoardEvent);
myKeyBoardEvent.Key = "C";

List will now contain: C, C, C

To fix this, make the myKeyBoardEvent local to the function and just create a new KeyboardEvent each time.

Here is a fixed version:

List<KeyboardEvent> keyList = new List<KeyboardEvent>();
List<WorkflowEvent> myLogs = new List<WorkflowEvent>();

public void LogKeyboadEvent(Key keyboard)
{
    KeyboardEvent myKeyBoardEvent = new KeyboardEvent();
    myKeyBoardEvent.Key = keyboard.ToString();
    keyList.Add(myKeyBoardEvent);
    myLogs.Add(myKeyBoardEvent);
}

Answer 2

This is basic problem. myKeyBoardEvent is a refference not a value and list contains reference to the same object.

Correct implementation would be:

public void LogKeyboadEvent(Key keyboard)
{
    keyBoardEvent = new KeyboardEvent();
    keyBoardEvent.Key = keyboard.ToString();
    keyList.Add(keyBoardEvent);
    myLogs.Add(keyBoardEvent);
}

Here it will work, BUT changing object on the myLogs list will change it on the keyList too. Other approach will take more memory, but will secure it from changes:

public void LogKeyboadEvent(Key keyboard)
{
    keyBoardEvent = new KeyboardEvent();
    keyBoardEvent.Key = keyboard.ToString();
    keyList.Add(keyBoardEvent);
    keyBoardEvent2 = new KeyboardEvent();
    keyBoardEvent2.Key = keyboard.ToString();
    myLogs.Add(keyBoardEvent2);
}

And third approach it would be to use List, but no code here mate.