How do I convert a “Keys” enum value to an “int” character in C#?

问题

This seems like something that should be easy, but I am having a tough time figuring out what needs to happen here.

In the "KeyDown" eventhandler, if the "e.KeyValue" is a number, I want to treat it as a number and store it as an int. So, if I hit "8" on the number pad, I don't want "Numpad8" I want the int value 8 that I can add or subtract or whatever.

So, how do I convert from the KeyValue to an int?

回答1:

I'd go with this solution:

int value = -1;
if (e.KeyValue >= ((int) Keys.NumPad0) && e.KeyValue <= ((int) Keys.NumPad9)) { // numpad
    value = e.KeyValue - ((int) Keys.NumPad0);
} else if (e.KeyValue >= ((int) Keys.D0) && e.KeyValue <= ((int) Keys.D9)) { // regular numbers
    value = e.KeyValue - ((int) Keys.D0);
}

...if the point was to get the numeric value of the label of they key that was punched in.

回答2:

Something like this should work well: (Edited)

int keyVal = (int)e.KeyValue;
int value = -1;
if ((keyVal >= (int)Keys.D0 && keyVal <= (int)Keys.D9)
{
    value = (int)e.KeyValue - (int)Keys.D0;
}
else if (keyVal >= (int)Keys.NumPad0 && keyVal <= (int)Keys.NumPad9)
{
    value = (int)e.KeyValue - (int)Keys.NumPad0;
}

回答3:

Facts: Keyboard has keys. Some keys represent numbers and some do not.

Problem (rephrased): Yield a numeric value represented by a key, if the key represents a number.

To solve the problem it is necessary to know which keys (out of set of all keys) represent numbers as well as exact numeric value each (number) key represents.

To my knowledge there is no an easy way to get such a mapping from the framework.

Note: The fact D0-D9 and NumPad0-NamPad9 are sequential in the Keys enum is accidental and relying on these values being ordered sequentially is unfounded.

So solution would be:

Determine if given key represents a number.
Return numeric value of the key if key represents a number.

private static readonly IDictionary<Keys, int> NumericKeys = 
    new Dictionary<Keys, int> {
        { Keys.D0, 0 },
        { Keys.D1, 1 },
        { Keys.D2, 2 },
        { Keys.D3, 3 },
        { Keys.D4, 4 },
        { Keys.D5, 5 },
        { Keys.D6, 6 },
        { Keys.D7, 7 },
        { Keys.D8, 8 },
        { Keys.D9, 9 },
        { Keys.NumPad0, 0 },
        { Keys.NumPad1, 1 },
        { Keys.NumPad2, 2 },
        { Keys.NumPad3, 3 },
        { Keys.NumPad4, 4 },
        { Keys.NumPad5, 5 },
        { Keys.NumPad6, 6 },
        { Keys.NumPad7, 7 },
        { Keys.NumPad8, 8 },
        { Keys.NumPad9, 9 }
   };

private int? GetKeyNumericValue(KeyEventArgs e) {
    if (NumericKeys.ContainsKey(e.KeyCode)) return NumericKeys[e.KeyCode];
    else return null;
}

Arguably, not the simplest solution, but the one that models the solution closely.

回答4:

Depending on how many keys you are keeping track of, the simplest method would be for you to create a select case (or switch statement in C# I guess?) that would check the value of your keydown and depending upon that value assign a value to an integer that is appropriate.

回答5:

If you want NUMERIC values, you'll have to create a switch(e.KeyCode) statement and evaluate the key and create your own int. There's no simple way to turn a Keys into a numeric value that represents the number on the key. The closest you could get might be the ASCII equivalent, which would still need to be translated.

回答6:

Could you just listen for the KeyPress event instead? It will give the character that was actually pressed.

回答7:

This function will do what you want:

private int GetKeyValue(int keyValue)
{
    if (keyValue >= 48 && keyValue <= 57)
    {
        return keyValue - 48;
    }
    else if (keyValue >= 96 && keyValue <= 105)
    {
        return keyValue - 96;
    }
    else
    {
        return -1; // Not a number... do whatever...
    }
}

Call it like so:

private void Form1_KeyDown(object sender, KeyEventArgs e)
{
    int num = GetKeyValue(e.KeyValue);  
}

回答8:

The KeyValue represents the character code for the key that was pressed. In order to obtain its numerical valaue you should find the character for the key that was pressed, then parse it from a character to an integer.

Something like Convert.ToInt32(e.KeyCode.ToString())

回答9:

Or create a extension method and call it like

private void Form1_KeyDown(object sender, KeyEventArgs e)
{    
    int num = e.KeyValue.GetKeyValue();  
}

where the extension method is

public static class MyExtensions
{
    public static int GetKeyValue(this int keyValue)
    {

        if (keyValue >= 48 && keyValue <= 57)
        {
            return keyValue - 48;
        }
        else if (keyValue >= 96 && keyValue <= 105)
        {
            return keyValue - 96;
        }
        else
        {
            return -1; // Not a number... do whatever...    }

        }
    }
}

回答10:

I used this 2 lines simple code:

string key = e.KeyCode.ToString();

if (key.Length > 1) key = key.Replace("NumPad", "").Replace("D", "");

回答11:

int i = (int)e.KeyValue;

来源：https://stackoverflow.com/questions/769529/how-do-i-convert-a-keys-enum-value-to-an-int-character-in-c

标签

winforms

keydown