C＃XNA键盘输入问题。 代码总是返回false

Question

I'm attempting to implement a way for the player to change controls, and then save that data to a text file.

Only my InputManager class uses the Xna.Input.Keys enum, everything else getting keyboard input passes in a string. The InputManager contains a dictionary with the key being the dynamic string passed in from outside, and the value is the corresponding key in the Input.Keys enum.

All this is loaded in from a file (keyconfig.cfg, just a standard text file).
I've tried modifying the code in various ways, but I can't seem to get it to work properly. The problem appears to be coming this particular method of mine, which is a part of the InputManager:

public bool IsButtonPressed(string keyString)
    {
        if (keyState.IsKeyDown(KeyFromString(keyString)) && keyState_old.IsKeyUp(KeyFromString(keyString)))
           return true;
        return false;
    }

• KeyFromString casts the string to a Keys type
• keyState & keyState_old are KeyboardState instances (_old being an image of last frame)
• The KeyboardState instances are updated every frame through an Update()

I'm setting my keyState & keyState_old variables within the Update() of the InputManager like so:

public void Update(GameTime gameTime)
{
    keyState = Keyboard.GetState();
    mouseState = Mouse.GetState();
    //Updates some other stuff within the class here, unrelated to keyboard input
    keyState_old = keyState;
}

I'm absolutely stuck on this, apologies if any of this is unclear, my english is not the best. Thanks in Advance.

Answer 1

It is probably safer to assign keyState_old before reading the new state to avoid overwriting it

public void Update(GameTime gameTime)
{
    keyState_old = keyState;  // Do this first

    keyState = Keyboard.GetState();  // Then this
    mouseState = Mouse.GetState();
    //Updates some other stuff within the class here, unrelated to keyboard input
}

Otherwise if a call is made to IsButtonPressed is made from outside the InputManager.Update method, the current and old key states will be the same value

Answer 2

keyState = Keyboard.GetState();
keyState_old = keyState;

This right here is your problem. You get the new state, and put it into keyState , and then you put keyState into keyState_old ... so you have two copies of the same state. Put these two lines together, rather than either side of that block of unrelated stuff, and do them the other way round. Save the old state, then get the new one.