问题

我明白了。以下是您想要的翻译：

假设我们创建了一个程序来计算一个科目的平均分，并输入了`test1`的分数和`test2`的分数，然后显示出平均分。

我们需要进行两次编辑来输入`test1`和`test2`，以及一次编辑来显示平均分。正如我们所知，`test1`或`test2`的分数，例如，如果是`15,5`，意味着这个分数如果是小数，将包含一个逗号，这意味着它不能是一个包含两个逗号的小数，例如`15,15,1`，因为这不是一个有效的小数。

我应该如何让程序用户只输入一个逗号，以避免出现错误消息呢？

如果我的解释不清楚，我为此道歉。我可以写哪段代码使用户只能输入一个逗号，以及我应该把它写在哪里？比如，在编辑框本身，或者在`OnChange`或`OnKeyPress`属性中，或者确切地说在哪里？

我尝试在`OnChange`事件中写了这段代码：

```pascal
if not ( Key in ['0'..'9'] + [',',#8] ) then Key := #0;

以便用户只能输入数字和逗号，#8用于删除已输入的内容。

但是尽管如此，他仍然可以输入包含多个逗号的数字，这意味着他仍然可以写入15,5,1或9,9,9，尽管我希望他只写一个有效的包含一个逗号的小数，因为一个小数不能包含多个逗号。

我认为解决办法可能是将条件*1应用于逗号，但我不知道如何实现这个想法。我的意思是逗号只能出现一次。

您认为呢？

<details>
<summary>英文:</summary>

Suppose we created a program to calculate the average of a subject and entered the `test1` point and the `test2` point, and then the average is displayed.

We need two edits to enter the `test1` and `test2`, and one edit to show the average. As we know, that the `test1` or `test2` point, for example, if it is `15,5` it means that the point, if it is decimal, will consist of a comma, meaning it cannot be a decimal number that contains two commas, for example `15,15,1`, as this is not a decimal number.

How can I make the user of my program enter only one comma, that is, how do I prevent him from entering several commas in order for error messages not to appear?

I apologize if my explanation was not clear. What is the code that I can write to make users enter only one comma, and where do I write it? For example, in the edit itself, or in the properties `OnChange` or `OnKeyPress`, or where exactly?

I tried writing this code in the `OnChange` event:

if not ( Key in ['0'..'9'] + [',',#8] ) then Key := #0;

to make the user write only the numbers and the comma, and let `#8` to erase what was written.

But despite this, he can enter a number that contains more than one comma, which means that he can still write, for example, `15,5,1` or `9,9,9`, although I want him to write only a valid decimal with one comma, because a decimal number can't contain more than one comma.

I think that the solution is, for example, to put the condition '*'*1, but I don't know how to employ the idea. I mean, the comma is multiplied once.

Or, what do you think?

</details>


# 答案1
**得分**: 1

我建议在实际进行计算时使用 [`TryStrToFloat()`](https://docwiki.embarcadero.com/Libraries/en/System.SysUtils.TryStrToFloat) 函数来验证用户的输入，该函数位于 `SysUtils` 单元中。这样可以让你进行自己的错误处理等。

例如：

```delphi
uses
  ..., SysUtils;

procedure TMyForm.GetAverageButtonClick(Sender: TObject);
var
  point1, point2: Double;
begin
  if not TryStrToFloat(Edit1.Text, point1) then
  begin
    ShowMessage('Point1 is not valid');
    Edit1.SetFocus;
    Exit;
  end;

  if not TryStrToFloat(Edit2.Text, point2) then
  begin
    ShowMessage('Point2 is not valid');
    Edit2.SetFocus;
    Exit;
  end;

  Edit3.Text := FloatToStr((point1 + point2) / 2.0);
end;

不要浪费时间和精力在每次按键时进行验证 - 特别是因为你并没有完全验证输入，比如你没有阻止用户输入超过一个逗号等。

uses
  ..., SysUtils;

procedure TMyForm.GetAverageButtonClick(Sender: TObject);
var
  point1, point2: Double;
begin
  if not TryStrToFloat(Edit1.Text, point1) then
  begin
    ShowMessage('Point1 is not valid');
    Edit1.SetFocus;
    Exit;
  end;

  if not TryStrToFloat(Edit2.Text, point2) then
  begin
    ShowMessage('Point2 is not valid');
    Edit2.SetFocus;
    Exit;
  end;

  Edit3.Text := FloatToStr((point1 + point2) / 2.0);
end;

答案2

得分: 0

你可以使用 Pos 函数来检查逗号是否已存在：

procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
begin
  if (Key = '.') and ('.' <> DecimalSeparator) then
    Key := DecimalSeparator;
  if not (Key in ['0'..'9', DecimalSeparator, #8]) then
  begin
    Key := #0;
    Beep;
    Exit;
  end;
  if (Key = DecimalSeparator)
    and (Pos(DecimalSeparator, TEdit(Sender).Text) > 0) then
  begin
    Key := #0;
    Beep;
  end;
end;

此外，如果用户使用数字键盘，它也接受点字符，并在需要时将其转换为十进制分隔符。

procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
begin
  if (Key = '.') and ('.' <> DecimalSeparator) then
    Key := DecimalSeparator;
  if not (Key in ['0'..'9', DecimalSeparator, #8]) then
  begin
    Key := #0;
    Beep;
    Exit;
  end;
  if (Key = DecimalSeparator)
    and (Pos(DecimalSeparator, TEdit(Sender).Text) > 0) then
  begin
    Key := #0;
    Beep;
  end;
end;