我有一个空的绘画事件，有时会开始无限循环。我不知道为什么。我允许用户单击按钮来输入表达式。用户单击确认后，我将开始简化他们输入的表达式，因为我要完成的程序是布尔代数简化程序。确认单击后，将调用某些子例程并完成一些验证。验证以条件语句的形式完成，例如if和else，并且如果表达式无效，则会显示一个消息框，否则将开始进行简化。我在下面显示了确认按钮单击事件和无限循环绘制事件。我不确定为什么有时会无限循环以及为什么有时会起作用。何时无限循环的一个例子是表达式中的第一个字符是'（'，但是它没有空值。
确认Btn点击事件：
private void ConfirmBtn_Click(object sender, EventArgs e)
{
string s = "";
char C = Expression.Text[Expression.Text.Length - 1];
if (!IsBalanced(Expression.Text))
{
MessageBox.Show("Invalid Expression. Sort out brackets", "Error!");
}
else if (C == '⊕' || C == '•' || C == '+')
{
MessageBox.Show("Invalid Expression. Cannot end on an operator", "Error!");
}
else if (UnconnectedOperatorErrorPresent(Expression.Text, NOTs))
{
MessageBox.Show("An operator cannot have more Nots over it than any of its adjacent variables.", "Error!");
}
else if (UnconnectedBracketError(Expression.Text, NOTs))
{
MessageBox.Show("A bracket cannot have more Nots over it than any of its adjacent variables.", "Error!");
}
else if (Expression.Text[0] == '(')
{
if (NOTs[0] > 0)
{
MessageBox.Show("A bracket at the beginning of the expression cannot have NOTs over it.", "Error!");
}
}
else if (Expression.Text[Expression.Text.Length - 1] == ')')
{
if (NOTs[Expression.Text.Length - 1] > 0)
{
MessageBox.Show("A bracket at the end of the expression cannot have NOTs over it.", "Error!");
}
}
else if (Expression.Text.Length > 20)
{
MessageBox.Show("Expression has a maximum length of 20 characters.", "Error!");
}
else
{
for (int i = 0; i < overLines.Length; i++)
{
overLines[i].Text = "";
}
int n = 0;
for (int i = 0; i < NOTs.Count; i++)
{
if (n < NOTs[i])
{
n = NOTs[i];
}
for (int y = 0; y < overLines.Length; y++)
{
if (y < NOTs[i])
{
overLines[y].Text += "_";
}
else
{
overLines[y].Text += " ";
}
}
}
Subroutines m = new Subroutines();
m.ExpressionLocation(n, Expression, 311, 132);
SimplifiedExpression = Simplify();
if (SimplifiedExpression == "0")
{
SimplifiedExpression = "0 or False";
NOTsNew.Clear();
}
if (SimplifiedExpression == "1")
{
SimplifiedExpression = "1 or True";
NOTsNew.Clear();
}
for (int i = 0; i < NOTsNew.Count; i++)
{
if (i > SimplifiedExpression.Length)
{
NOTsNew.RemoveAt(i);
}
}
SimplifiedExpressionForm SEF = new SimplifiedExpressionForm(Expression, NOTsNew, SimplifiedExpression);
SEF.Show();
ResetVariables();
}
}
按钮和输出表达式的标签在面板顶部。 这是绘画事件：
private void BackgroundPanel_Paint(object sender, PaintEventArgs e)
{
}
我认为，与其在其中包含一个if if然后一个if，不如在一个if条件中包含初始条件和if包含在if内部的条件，这会更好，例如：
else if (Expression.Text[0] == '(' && NOTs[0] > 0)
{
MessageBox.Show("A bracket at the beginning of the expression cannot have NOTs over it.", "Error!");
}
而不是：
else if (Expression.Text[0] == '(')
{
if (NOTs[0] > 0)
{
MessageBox.Show("A bracket at the beginning of the expression cannot have NOTs over it.", "Error!");
}
}
但是为什么在else if中的if如果不起作用/会导致绘画事件无限循环？