Computing Form Location with Button

Question

I'm working on a programming assignment, and I'm trying to make this button take the values from two textboxes, and calculate the new location for the form window. I'm having trouble converting the textbox values to type int, and being made usable by the btnCompute_click method.

    private void btnCompute_Click(object sender, EventArgs e)
    {
        int x = Convert.ToInt32(txtXvalue);
        int y = Convert.ToInt32(txtYvalue);
        Location = new Point(x,y);
    }

    private void xValue_TextChanged(object sender, EventArgs e)
    {
        int xValue =
            Convert.ToInt32(txtXvalue);
    }

    private void yValue_TextChanged(object sender, EventArgs e)
    {
        int y =
            Convert.ToInt32(txtYvalue);
    }

I forgot to add some additional info, the acceptable values for x and y must be positive. Would I use an if...else statement to control the acceptable values?

Answer 1

user29... i have no idea why death... replied that. it makes no sense to me. but you question makes sense to me. i suppose death... did not understand your question.

First off, everything you ask does not need anything in the TextChanged methods. Do all your handling in the btnCompute_Click() method because you want to do something *when you click your button, not when the user edits the text of the text boxes, according to your question.

The code that is in your TextChanged() methods will get executed whenever the Text values of those text boxes change. that's not what you asked for it to do. But you could use these events for example, if you wanted a label to become visible or hidden and to set the text of a label which shows text, so you can use it as an error message label, for instance if the integer value of a text box is negative or even if it cannot be parsed.

So in your btnCompute_Click() methods, you first want to get the int values. You need to decide exactly what you want your code to do if the text is not integers. In my opinion, most beginners code things like message boxes or something. I like to give the user feedback with Labels or a status bar message, depending on what I feel is appropriate. Since my first choice would be to use a Label to show the 'error' message when text boxes cannot be parsed to integers, then i would simply return from the button click method without doing anything when the values are not what i want. That way the user gets their messages without annoying popup message boxes or anything. But it's up to you whether you want to pop up a message box or not. Others have given you good code to do that. I want to give you good code that avoids what i consider annoying popup boxes.

When converting strings to an int, Convert.ToInt32 will throw an error if the string cannot be parsed. int.TryParse is the silver bullet for truly parsing strings to integers without any error. Here is the entire code i would use. I made a new project just to make sure i'm not giving you buggy code. I give you my code on how I handle this.

In your updated prerequisite, you mention x & y must be positive and not negative. I note to you that these are not the same. For instance, 0 is neither positive nor negative. I assume that you technically mean that x and y cannot be negative, (and that it does not need to be positive, since 0 should be allowed).

    private void Form1_Load(object sender, EventArgs e)
    {
        lblErrorX.Text = null;
        lblErrorY.Text = null;
    }

    private void btnMoveForm_Click(object sender, EventArgs e)
    {
        int x = 0; if (int.TryParse(txtX.Text, out x) == false) { return; }
        int y = 0; if (int.TryParse(txtY.Text, out y) == false) { return; }
        if (x < 0 || y < 0) { return; }
        this.Location = new Point(x, y);
    }

    private void txtX_TextChanged(object sender, EventArgs e)
    {
        int x = 0;
        if (int.TryParse(txtX.Text, out x) == false)
        { lblErrorX.Text = "X is not an valid integer."; return; }
        if (x < 0) { lblErrorX.Text = "X cannot be negative."; return; }
        lblErrorX.Text = null;
    }

    private void txtY_TextChanged(object sender, EventArgs e)
    {
        int y = 0;
        if (int.TryParse(txtY.Text, out y) == false)
        { lblErrorY.Text = "Y is not an valid integer."; return; }
        if (y < 0) { lblErrorY.Text = "Y cannot be negative."; return; }
        lblErrorY.Text = null;
    }

In my project, on the form, in the following left to right order: lblX, txtX, lblErrorX. I have the same corresponding for Y: lblY, txtY, lblErrorY. Then i have one Button: btnMoveForm. So my txtX corresponds to your txtXvalue. my btnMoveForm corresponds to your btnCompute, but to me, 'compute' means to calculate, which is not really what this button is doing. this button is moving the form, so that's why i name it as such.

I have played with setting both the Location and the DesktopLocation and it seems to do the same thing. I've always used Location and i just learned that DesktopLocation works too, but since Location is shorter, i use it.

Someone asked why i don't use if(!int.TryParse(...)) { return; } rather than my if(int.TryParse(...) == false) { return; }. My reason is unfortunately that i think ! is an easy one character to miss when reading code, so i avoid it, especially when that little mistake means the opposite of what the code really would do. So my use of '== false' is always for human clarity. But i do like the C# ease of only needing one character. I just think it's a shame that in my opinion, it's a lot safer to write code that is better for humans so we don't mistake it. That's the only reason i use '== false' instead of !. Use ! if you like. It's quite convenient. I regret not using it. hehe.

Oh, and the reason i set the lblErrorX.Text = null; and lblErrorY.Text = null; is on my form in design view, i give them a text value so i can see them. :) so when the program runs, i set the Text to be blank. But you can use the Visible property if you prefer. I just leave them always visible and only set their Text properties.

Answer 2

I think you are looking for this.

private void btnCompute_Click(object sender, EventArgs e)
{
    int x = Convert.ToInt32(txtXvalue.Text);
    int y = Convert.ToInt32(txtYvalue.Text);
    DesktopLocation = new Point(Math.Abs(x), Math.Abs(y));

}

This gets the location for the desktop. Also you need the .Text to get the text inside the textbox. You should also check to make sure the text is not null or empty before using or it will cause an error. If this isn't what you are looking for please explain a little more.

Answer 3

Based on your expanded criteria you can check for negative numbers conditionally or use Math.Abs to get the absolute value. Something like this.

int x, y;

if (int.TryParse(txtXvalue.Text, out x) && int.TryParse(txtYvalue.Text, out y))
{
    if (x < 0 || y < 0)
    {
        MessageBox.Show("Negative numbers not allowed");
    }
    else
        Location = new Point(x, y);

}
else
{
    MessageBox.Show("Must be an Integer");
}

or

int x, y;

if (int.TryParse(txtXvalue.Text, out x) && int.TryParse(txtYvalue.Text, out y))
{
    Location = new Point(Math.Abs(x), Math.Abs(y));
}
else
{
    MessageBox.Show("Must be an Integer");
}