c# - 如何解决 C# 中的“InvalidCastException”？

Question

我收到一个运行时错误，它告诉我它无法将 PictureBox 类型的对象转换为 MusicNote 类型（MusicNote 继承自 PictureBox。）

private void Note_MouseDown(object sender, MouseEventArgs e)
    {
        //try
        //{
            foreach (MusicNote mn in panel2.Controls) //this is where the error occurs
            {
                if (sender == mn)
                {
                    if (e.Button == MouseButtons.Right)
                    {
                        count = 0;
                        timer1.Start();
                        sp.SoundLocation = MusicNote_path + mn.note + ".wav";
                        sp.Play();
                    }
                if (e.Button == MouseButtons.Left)
                {
                    dragging = true;
                    mn.BackColor = Color.HotPink;


                }

下面是 MusicNote 类的一部分，包括构造函数，展示了每次构造 MusicNote 时会发生什么：

class MusicNote : PictureBox
{
    public int notepitch;
    public int noteduration;
    public String noteshape;
    public String note;
    enum Accid { sharp, flat, sole };

    public static String NoteImage_path = Environment.CurrentDirectory + @"\Notes-Images\\";
    public static int xLoc = 30;
    public int yLoc = 0;

    System.Timers.Timer timer1 = new System.Timers.Timer();

    public MusicNote(int iNotepitch, int iDuration, String iBnoteShape, String iNote)
    {
        notepitch = iNotepitch;
        noteduration = iDuration;
        noteshape = iBnoteShape;
        note = iNote;


        ImageLocation =  NoteImage_path + noteshape + ".bmp";
        BackColor = Color.Transparent;
        ClientSize = new Size(35, 35);
        //BringToFront();


        Location = new Point(xLoc, getyLoc(iNote));
        xLoc += 37;
    }

这是面板的填充方式：

MusicNote mn = new MusicNote(mk.getMusicNote(), duration, bNoteShape, mk.getNote());
mn.MouseDown += new MouseEventHandler(Note_MouseDown);
mn.MouseUp += new MouseEventHandler(Note_MouseUp);
mn.MouseClick += new MouseEventHandler(Note_MouseClick);

panel2.Controls.Add(mn); //adding MusicNote component to MusicStaff (panel2) collection

编辑：您可以在此处查看错误。

任何帮助表示赞赏，谢谢。

标签： c#formscastingpicturebox

Answer 1

要仅循环MusicNote实例，您可以使用OfTypeLINQ 中的扩展方法：

foreach (MusicNote mn in panel2.Controls.OfType<MusicNote>()) {
   // do stuff
}