Question

public abstract class Cell : INotifyPropertyChanged
{
    protected string text;
    protected string value;
    readonly int rowIndex;
    readonly int columnIndex;

    public Cell()
    {
    }

    public Cell(int ri, int ci)
    {
        rowIndex = ri;
        columnIndex = ci;
    }

    public Cell CreateCell()
    {
        return this;
    }

    public string Value
    {
        get { return value; }
    }

    public int RowIndex 
    {
        get { return rowIndex; }
    }

    public int ColumnIndex
    {
        get { return columnIndex; }
    }



    public string Text
    {
        get
        {
            return text;
        }
        set
        {
            text = value;

            this.OnPropertyChanged("text");
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    // Create the OnPropertyChanged method to raise the event 
    protected virtual void OnPropertyChanged(string propertyName = "")
    {
        var eventHandler = this.PropertyChanged;

        if (eventHandler != null)
        {
            eventHandler.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }

}

public class SpreadSheet
    {
        private sCell[,] cellGrid;
        private int rows, cols;
    private int RowCount
    {
        get { return rows; }
    }

    private int ColumnCount
    {
        get { return cols; }
    }

    private class sCell : Cell
    {
        public sCell(int ri, int ci) : base(ri, ci)
        {
        }

        public static sCell createCell(int ri, int ci)
        {
            return new sCell(ri, ci);
        }

        public void setValue(sCell[,] cellGrid)
        {
            string thisText = this.Text;

            if (thisText[0] == '=')
            {
                byte[] asciiBytes = ASCIIEncoding.ASCII.GetBytes(thisText);

                this.value = cellGrid[asciiBytes[1] - 65, asciiBytes[2]].Value;
            }
            else
            {
                this.value = thisText;
            }

        }

    }

    public event PropertyChangedEventHandler CellPropertyChanged;

    public SpreadSheet(int numRows, int numColumns)
    {

        PropertyChangedEventHandler handler = CellPropertyChanged;

        cellGrid = new sCell[numRows, numColumns];

        rows = numRows;
        cols = numColumns;

        int i, j;

        for (i = 0; i < rows; i++)
        {
            for(j = 0; j < cols; j++)
            {
                sCell newCell = sCell.createCell(i, j);
                cellGrid[i, j] = newCell;
                newCell.PropertyChanged += handler;
            }
        }
    }

    public Cell getCell(int ri, int ci)
    {
        if (cellGrid[ri, ci] != null)
        {
            return cellGrid[ri, ci];
        }
        else
        {
            return null;
        }

    }

    protected void OnCellPropertyChanged(Cell c, string text)
    {
        PropertyChangedEventHandler handler = CellPropertyChanged;

        if (handler != null)
        {
            handler(c, new PropertyChangedEventArgs(text));
        }
    }

    private void handler(object sender, PropertyChangedEventArgs e)
    {
        sCell c = sender as sCell;

        c.setValue(this.cellGrid);

        OnCellPropertyChanged(sender as Cell, "CellValue");
    }

}

为什么事件处理程序始终为null。我订阅从抽象Cell继承的Cell的每个实例到事件，它仍然保持为空。

Answer 1

在SpreedSheet构造函数中，删除以下行：

PropertyChangedEventHandler handler = CellPropertyChanged;

它看起来应该正确订阅 - 这会覆盖SpreadSheet.handler方法。

INotifyPropertyChanged（如何订阅事件以及为什么eventhandler始终为null）

1 个答案: