Adding Double, String value on listbox.

Song Lee

Hello,

I'm trying to make listbox show a few string and double values when button is pressed.

However, I'm getting errors: Cannot implicitly convert type 'string' to 'double' When ever I put double agestr = ageText.Text;

How can I make it so agestr and teethstr text box only accepts double values?

private void addButton_Click(object sender, EventArgs e)

{

string namestr = nameText.Text;

string agestr = ageText.Text; //This needs to be double, not string

string genderstr = genderList.Text;

string teethstr = teethText.Text; //This needs to be double, not string

string tailstr = tailText.Text;

string row = String.Format("{0} {1} {2} Has {3} teeth. tail is {4} cm long", namestr, agestr, genderstr, teethstr, tailstr);

listBox.Items.Add(row);

}

3 Replies

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Vulpes11y ago
There are basically two ways of validating numbers typed into a TextBox:

1. To check each character as it's typed.

2. To wait until the user has entered the number and then validate it.

To do #1 properly is quite difficult as you need to check not only what's being typed but anything that might be pasted in as well. Also, it's even more difficult to restrict the number to a reasonable range.

#2 is far easier and you're on the right lines with what you've just posted. I'd suggest instead for the whole method:

private void addButton_Click(object sender, EventArgs e)
{
string name = nameText.Text;
if (name.Length == 0)
{
MessageBox.Show("Please enter a name.");
nameText.Focus();
return;
}

double age;
bool isValid = Double.TryParse(ageText.Text, out age);
if (!isValid || age < 0 || age > 125)
{
MessageBox.Show("Age must be a number between 0 and 125. Please amend.");
ageText.Focus();
return;
}

string gender = genderList.Text;

int teeth;
isValid = Int32.TryParse(teethText.Text, out teeth);
if (!isValid || teeth < 0 || age > 250)
{
MessageBox.Show("Teeth must be a number between 0 and 250. Please amend.");
teethText.Focus();
return;
}

double tail;
isValid = Double.TryParse(tailText.Text, out tail);
if (!isValid || tail < 0 || age > 300)
{
MessageBox.Show("Tail must be a number between 0 and 300. Please amend.");
tailText.Focus();
return;
}

string row = String.Format("{0} {1} {2} Has {3} teeth. tail is {4} cm long", name, age, gender, teeth, tail);
listBox.Items.Add(row);
}
0
Song Lee11y ago
Thanks for the reply, but I still haven't really understood.
I am trying to validate it so it only accepts Double value, not string.
This is the error that I got : "double is a type but is used like a variable"

I also added this:

Double agestr;
agestr = Double.Parse(ageText.Text);

if (Double.Parse(ageText.Text) =! Double) //Getting error here
{
MessageBox.Show("Age must be Double Value");
return;
}

Thank you for the help!
0
Vikram Agrawal11y ago

Hi Song Lee,
You should validate your age and teeth textbox so that user will not able to enter any non numeric value in those text boxes
You can write this validation code in TextBox_KeyPress Event
Thank You
+1