C# 不能使用 IF 语句中的变量

Question

我正在制作简单的密码生成器，但我无法从 try 中选择 int 并从 if 中选择 string。这是代码。我希望你能帮助我。我不能把它作为文本框，我不能用它做任何事情。

private void button3_Click(object sender, EventArgs e)
{
    try
    {
        int i = Int32.Parse(textBox2.Text);
        return;
    }
    catch
    {

    }
    CreatePassword(i);
}

这是CreatePassword函数的一部分

public string CreatePassword(int length)
{
    if (checkBox2.Checked)
    {
        const string src = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
        return src;
    }
    else
    {
        const string src = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
        return src;
    }
}

Answer 1

您的代码存在几个问题。首先，您试图在声明的范围之外访问变量i；它在 try 语句之外不可见。其次，您似乎希望从您解析的整数生成密码，但您在创建密码之前明确返回。第三，你没有对创建的密码做任何事情，只是把它扔掉。

尝试以下方法：

    private void button3_Click(object sender, EventArgs e)
    {
        try
        {
            int i = Int32.Parse(textBox2.Text);
            string password = CreatePassword(i);
            // TODO: use the 'password' string for something.
            return;
        }
        catch
        {

        }
    }

您还应该考虑改用int.TryParse，它不会引发异常。

    if (int.TryParse(textbox2.Text, out int i) {
        string password = CreatePassword(i);
        // Do something with 'password' 
    } else {
        // Display an error.
    }

Answer 2

从您的示例看来，您需要的只是Int32.TryParse：

int.TryParse(textBox2.Text, out int i);
CreatePassword(i);

但是，要回答您最初的问题：您需要在 try 块之外初始化 i 变量，以便能够在它之后使用它。例如：

        int i = 0;
        try
        {
            i = int.Parse("test");
        }
        catch
        {

        }
        Console.WriteLine(i); // 0

Answer 3

你的逻辑有点缺陷。如果 Textbox2 不包含有效整数，则忽略异常并仅创建密码。您希望创建什么样的密码？

我认为你的意思是这样做：

private void button3_Click(object sender, EventArgs e)
    {
        try
        {
            int i = Int32.Parse(textBox2.Text);
            CreatePassword(i);
        }
        catch
        {
            // Show a messagebox or something
        }
    }

Answer 4

感谢大家的帮助。我做到了。在这里，您有我的应用程序的来源，谢谢大家。我的应用程序完全可以运行，我相信您理解我的逻辑：D

using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Password_generator
{
    public partial class Form1 : Form
    {
        private bool _dragging = false;
        private Point _start_point = new Point(0, 0);
        public Form1()
        {
            InitializeComponent();
        }

        public string CreatePassword(int length)
        {
            string src;
            var sb = new StringBuilder();
            Random RNG = new Random();

            src = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

            if (checkBox2.Checked)
            {
                src += "1234567890";
            }
            if (checkBox3.Checked)
            {
                src += "@#$%^&*()";
            }
            for (var i = 0; i < length; i++)
            {
                var c = src[RNG.Next(0, src.Length)];
                sb.Append(c);
            }
            textBox1.Text = sb.ToString();

            if (checkBox1.Checked)
            {
                try
                {
                    File.AppendAllText("hesla.txt", textBox1.Text + Environment.NewLine);
                }
                catch(Exception o)
                {
                    MessageBox.Show("Něco se nepovedlo! " + Environment.NewLine + "(" + o.Message + ")");
                }
            }

            return textBox1.Text;

        }

        private void button3_Click(object sender, EventArgs e)
        {
            try
            {
                int i = Int32.Parse(textBox2.Text);
                CreatePassword(i);
            }
            catch
            {
                MessageBox.Show("Musíš zadat číslo!");
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            this.Close();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            this.WindowState = FormWindowState.Minimized;
        }

        private void panel1_MouseUp(object sender, MouseEventArgs e)
        {
            _dragging = false;
        }

        private void panel1_MouseMove(object sender, MouseEventArgs e)
        {
            if (_dragging)
            {
                Point p = PointToScreen(e.Location);
                Location = new Point(p.X - this._start_point.X, p.Y - this._start_point.Y);
            }
        }

        private void panel1_MouseDown(object sender, MouseEventArgs e)
        {
            _dragging = true;
            _start_point = new Point(e.X, e.Y);
        }

        private void panel3_Paint(object sender, PaintEventArgs e)
        {

        }

        private void checkBox3_CheckedChanged(object sender, EventArgs e)
        {

        }

        private void checkBox2_CheckedChanged(object sender, EventArgs e)
        {

        }

        private void checkBox1_CheckedChanged(object sender, EventArgs e)
        {

        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {

        }

        private void label3_Click(object sender, EventArgs e)
        {

        }

        private void label1_Click(object sender, EventArgs e)
        {

        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void button4_Click(object sender, EventArgs e)
        {
            try
            {
                Clipboard.SetText(textBox1.Text);
            }
            catch
            {

            }
            
        }
    }
}