桌面健身软件：表单数据回显至pg_KurzfristigeTrainingsplanung页面失败

我正在开发一款健身桌面软件，主窗体中有「短期计划」页面pg_KurzfristigeTrainingsplanung。从该页面调用表单frm_KurzfristigeTrainingsplanung录入训练日期与内容，希望通过按钮将数据回显至原页面，且数据需持久保留（含关闭程序后）。

尝试以下代码实现数据回传，但执行后pg_KurzfristigeTrainingsplanung页面未显示预期数据：

private void btnEintragen_Click(object sender, EventArgs e)
{
    pg_KurzfristigeTrainingsplanung pgKF = pg_KurzfristigeTrainingsplanung;

    // Schleife von 1 bis 7
    for (int i = 1; i <= 7; i++)
    {
        if (i == 1)
        {
            // Spezialfall für i = 1: DateTimePicker und TextBox
            DateTimePicker dtpDatum1 = (DateTimePicker)this.Controls.Find("dtpDatum1", true).FirstOrDefault();
            Label lblDatum1 = (Label)pgKF.Controls.Find("lblDatum1", true).FirstOrDefault();

            if (dtpDatum1 != null)  // && lblDatum1 != null
            {
                lblDatum1.Text = dtpDatum1.Value.ToString("dd.MM.yyyy");
            }
        }
        else
        {
            // Standardfall für i = 2 bis 7: Labels
            Label lblDatumFormKF = (Label)this.Controls.Find("lblDatum" + i, true).FirstOrDefault();
            Label lblTrainingFormKF = (Label)this.Controls.Find("lblTraining" + i, true).FirstOrDefault();
            Label lblFocusFormKF = (Label)this.Controls.Find("lblFocus" + i, true).FirstOrDefault();

            Label lblDatumpgKF = (Label)pgKF.Controls.Find("lblDatum" + i, true).FirstOrDefault();
            Label lblTrainingpgKF = (Label)pgKF.Controls.Find("lblTraining" + i, true).FirstOrDefault();
            Label lblFocuspgKF = (Label)pgKF.Controls.Find("lblFocus" + i, true).FirstOrDefault();

            // Falls die Controls gefunden wurden, deren Text übertragen
            if (lblDatumFormKF != null && lblDatumpgKF != null)
            {
                lblDatumpgKF.Text = lblDatumFormKF.Text;
            }

            if (lblTrainingFormKF != null && lblTrainingpgKF != null)
            {
                lblTrainingpgKF.Text = lblTrainingFormKF.Text;
            }

            if (lblFocusFormKF != null && lblFocuspgKF != null)
            {
                lblFocuspgKF.Text = lblFocusFormKF.Text;
            }
        }
    }

    //Schliesst die Form nach erfolgreichem Eintragen der Daten
    this.Close();
}

一、修复数据回显失效问题 #

代码核心问题是未获取到主窗体中正在显示的pg_KurzfristigeTrainingsplanung实例，直接引用类名无法指向当前页面对象；同时空引用判断不完整，可能导致赋值逻辑未执行。

1. 传递正确的页面实例 #

在主页面调用表单时，将当前页面实例传递给表单：

// 主页面中打开表单的代码
frm_KurzfristigeTrainingsplanung frm = new frm_KurzfristigeTrainingsplanung();
frm.TargetPage = this; // 表单新增属性接收目标页面
frm.ShowDialog();

在表单类中新增属性：

public pg_KurzfristigeTrainingsplanung TargetPage { get; set; }

2. 修正按钮点击事件中的实例引用 #

替换原代码中的pg_KurzfristigeTrainingsplanung pgKF = pg_KurzfristigeTrainingsplanung;为：

var pgKF = TargetPage;

3. 补全空引用判断 #

将第1天的判断条件补全，避免空引用导致赋值失败：

if (dtpDatum1 != null && lblDatum1 != null)
{
    lblDatum1.Text = dtpDatum1.Value.ToString("dd.MM.yyyy");
}

二、实现数据持久化 #

要实现关闭程序后数据保留，需将数据序列化存储到本地（推荐JSON文件，轻量易实现）。

1. 创建训练计划实体类 #

public class TrainingPlanItem
{
    public DateTime Date { get; set; }
    public string TrainingContent { get; set; } = string.Empty;
    public string Focus { get; set; } = string.Empty;
}

public class ShortTermTrainingPlan
{
    public List<TrainingPlanItem> Items { get; set; } = new List<TrainingPlanItem>();
}

2. 表单中收集并保存数据 #

修改按钮点击事件，先收集数据到实体，再序列化到文件，最后更新主页面：

private void btnEintragen_Click(object sender, EventArgs e)
{
    // 1. 收集表单数据到实体
    var plan = new ShortTermTrainingPlan();

    // 处理第1天
    DateTimePicker dtpDatum1 = (DateTimePicker)this.Controls.Find("dtpDatum1", true).FirstOrDefault();
    TextBox txtTraining1 = (TextBox)this.Controls.Find("txtTraining1", true).FirstOrDefault();
    TextBox txtFocus1 = (TextBox)this.Controls.Find("txtFocus1", true).FirstOrDefault();
    if (dtpDatum1 != null)
    {
        plan.Items.Add(new TrainingPlanItem
        {
            Date = dtpDatum1.Value,
            TrainingContent = txtTraining1?.Text ?? string.Empty,
            Focus = txtFocus1?.Text ?? string.Empty
        });
    }

    // 处理第2-7天
    for (int i = 2; i <= 7; i++)
    {
        Label lblDatum = (Label)this.Controls.Find("lblDatum" + i, true).FirstOrDefault();
        Label lblTraining = (Label)this.Controls.Find("lblTraining" + i, true).FirstOrDefault();
        Label lblFocus = (Label)this.Controls.Find("lblFocus" + i, true).FirstOrDefault();
        if (lblDatum != null && DateTime.TryParse(lblDatum.Text, out DateTime date))
        {
            plan.Items.Add(new TrainingPlanItem
            {
                Date = date,
                TrainingContent = lblTraining?.Text ?? string.Empty,
                Focus = lblFocus?.Text ?? string.Empty
            });
        }
    }

    // 2. 序列化到JSON文件（存储在应用数据目录，避免权限问题）
    string appDataPath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), "FitnessApp");
    Directory.CreateDirectory(appDataPath);
    string filePath = Path.Combine(appDataPath, "ShortTermPlan.json");
    string json = JsonSerializer.Serialize(plan);
    File.WriteAllText(filePath, json);

    // 3. 更新主页面显示
    if (TargetPage != null)
    {
        TargetPage.LoadTrainingPlan(plan);
    }

    this.Close();
}

3. 主页面加载数据 #

在pg_KurzfristigeTrainingsplanung中添加加载数据的方法，页面初始化时自动加载：

public void LoadTrainingPlan(ShortTermTrainingPlan plan = null)
{
    // 若未传入数据，从文件读取
    if (plan == null)
    {
        string filePath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), "FitnessApp", "ShortTermPlan.json");
        if (File.Exists(filePath))
        {
            string json = File.ReadAllText(filePath);
            plan = JsonSerializer.Deserialize<ShortTermTrainingPlan>(json);
        }
        else
        {
            plan = new ShortTermTrainingPlan();
        }
    }

    // 更新页面控件
    // 第1天
    Label lblDatum1 = (Label)this.Controls.Find("lblDatum1", true).FirstOrDefault();
    Label lblTraining1 = (Label)this.Controls.Find("lblTraining1", true).FirstOrDefault();
    Label lblFocus1 = (Label)this.Controls.Find("lblFocus1", true).FirstOrDefault();
    if (plan.Items.Count >= 1 && lblDatum1 != null)
    {
        lblDatum1.Text = plan.Items[0].Date.ToString("dd.MM.yyyy");
        lblTraining1.Text = plan.Items[0].TrainingContent;
        lblFocus1.Text = plan.Items[0].Focus;
    }

    // 第2-7天
    for (int i = 2; i <= 7; i++)
    {
        int itemIndex = i - 1;
        Label lblDatum = (Label)this.Controls.Find("lblDatum" + i, true).FirstOrDefault();
        Label lblTraining = (Label)this.Controls.Find("lblTraining" + i, true).FirstOrDefault();
        Label lblFocus = (Label)this.Controls.Find("lblFocus" + i, true).FirstOrDefault();
        if (itemIndex < plan.Items.Count && lblDatum != null)
        {
            lblDatum.Text = plan.Items[itemIndex].Date.ToString("dd.MM.yyyy");
            lblTraining.Text = plan.Items[itemIndex].TrainingContent;
            lblFocus.Text = plan.Items[itemIndex].Focus;
        }
    }
}

// 页面加载时自动读取数据
private void pg_KurzfristigeTrainingsplanung_Load(object sender, EventArgs e)
{
    LoadTrainingPlan();
}

内容的提问来源于stack exchange，提问作者Dominique Müller