C＃忽略空的文本框

Question

I have ha a WinForms app with some textboxes . At the moment the app is simple and i only want to test how it will work. It will get mutch more complex in the future. What i tried to do create a rule to ignore empty textboxes or if empty use the value 0. The code i have is this one:

    decimal ata;
    decimal a1;
    decimal a2;
    decimal a3;
    decimal a4;
    decimal a5;
    decimal j = 0;

    a1 = decimal.TryParse(textBox1.Text, out j);
    a2 = decimal.Parse(textBox2.Text);
    a3 = decimal.Parse(textBox4.Text);
    a4 = decimal.Parse(textBox10.Text);
    a5 = decimal.Parse(textBox24.Text);
    ata = a1 + a2 + a3 + a4 + a5;

resposta.Text = ata.ToString();

i get an error "Cannot implicitly convert type 'bool' to 'decimal' in the line:

 a1 = decimal.TryParse(textBox1.Text, out j);

Can anyone help me with this problem.

Thanks in advance,

Answer 1

Use decimal.TryParse(textBox1.Text, out j); instead of a1 = decimal.TryParse(textBox1.Text, out j); . Your value is returned in j

Answer 2

You declared

decimal a1;

Then you tried:

a1 = decimal.TryParse(textBox1.Text, out j);

decimal.TryParse returns a bool not a decimal

j

Is taking the parsed value

Answer 3

The TryParse method returns a bool value to indicate whether conversion succeeded or not. The real value is returned in the second parameter ( out parameter).

You could try:

if (Decimal.TryParse(textBox1.Text, out j))
   a1 = j;

This only sets a1 if parsing was successful. Otherwise a1 keeps its previous value.

Answer 4

the return value TryParse is a bool . It indicates whether the conversion was successful or not. Usually you would use it like this:

decimal j;

if (decimal.TryParse(textBox1.Text, out j))
{
    // here the conversion worked and it is save to use j
}

You check whether it was successful and in this case you can use the value of the converted variable, otherwise it will remain null .

Here is the documentation

In respect to the value that is passed via the out keyword the documentation says: ( s is equivalent to textBox1.Text and result is equivalent to j )

When this method returns, result contains the Decimal number that is equivalent to the numeric value contained in s, if the conversion succeeded, or is zero if the conversion failed. The conversion fails if the s parameter is null or String.Empty, is not a number in a valid format, or represents a number less than MinValue or greater than MaxValue. This parameter is passed uninitialized; any value originally supplied in result will be overwritten.

Answer 5

The way you want to use the TryParse() method is like so

decimal a1 = 0;
bool parsed = decimal.TryParse(textBox1.Text, out a1);

if(parsed)
{
    //your arithmetic
}
else
{
    //throw error
}

Answer 6

The error is because TryParse() returns a boolean, not a decimal. You need to write explicit if statements to test if the textboxes are empty. You should consider wrapping this in a method.

Answer 7

You are trying to assign a bool value to a decimal variable that's why getting this error. Decimal.TryParse() will return bool value, Please take a look here you can use this value to check parsing is successful or not.

You will get result in your out parameter ie j.

Answer 8

One of the nice things of object oriented programming is reusability of code in similar situations.

You mentioned you are going to use some kind of "nullable decimal text boxes" a lot of times. Why not create a class for it? You'll only have to create the class once, and everyone who needs your nullable decimal text box (especially you with all your text boxes) can reuse this one code.

Bonus: if you ever need to change the behaviour of this kind of text boxes, for instance get a yellow background when empty, all your special text boxes instantaneously behave the same.

• To make it possible to ignore empty text boxes you need a property IsEmpty
• Property Value returns the Value of the text box as a decimal or 0M if IsEmpty

• What do you want to return if not empty but text is not a decimal?

  public class MyNullableTextBox : TextBox { public bool IsEmpty {get{return String.IsNullOrEmpty(base.Text);} }

   public decimal Value { get { if (this.IsEmpty) return 0M; else { decimal parsedValue; bool parsed = Decimal.TryParse(base.Text, out parsedValue); if (!parsed) // decide what you want in this case else return parsedValue; } } } 

  }

The nice thing is, that once you've added this (as a reference) to your solution, it can be found in the Toolbox and used in your forms designer as if it was a regular text box