我想从数据网格视图中打印文件。但是，一旦我点击“打印预览”，就会出现错误并显示：Object reference not set to an instance of an object。以下是错误：
arrColumnLefts.Clear();
在：
void printDocument1_BeginPrint(object sender, PrintEventArgs e)
{
try
{
strFormat = new StringFormat();
strFormat.Alignment = StringAlignment.Center;
strFormat.LineAlignment = StringAlignment.Center;
strFormat.Trimming = StringTrimming.EllipsisCharacter;
arrColumnLefts.Clear();
arrColumnWidths.Clear();
iCellHeight = 0;
iRow = 0;
bFirstPage = true;
bNewPage = true;
iTotalWidth = 0;
foreach (DataGridViewColumn dgvGridCol in dataGridView1.Columns)
{
iTotalWidth += dgvGridCol.Width;
}
}
catch (Exception ex)
{
SystemManager.ShowMessageBox("Message: " + ex.Message, "Error", 1);
}
}
和
arrColumnLefts.Add(iLeftMargin);
foreach (DataGridViewColumn GridCol in dataGridView1.Columns)
{
e.Graphics.FillRectangle(new SolidBrush(Color.Aqua), new Rectangle((int)arrColumnLefts[iCount], iTopMargin, (int)arrColumnWidths[iCount], iHeaderHeight));
e.Graphics.DrawRectangle(Pens.Black, new Rectangle((int)arrColumnLefts[iCount], iTopMargin, (int)arrColumnWidths[iCount], iHeaderHeight));
e.Graphics.DrawString(GridCol.HeaderText, GridCol.InheritedStyle.Font, new SolidBrush(GridCol.InheritedStyle.ForeColor), new RectangleF((int)arrColumnLefts[iCount], iTopMargin, (int)arrColumnWidths[iCount], iHeaderHeight), strFormat);
iCount++;
}
foreach (DataGridViewCell Cel in GridRow.Cells)
{
if (Cel.Value != null)
{
e.Graphics.DrawString(Cel.Value.ToString(), Cel.InheritedStyle.Font, new SolidBrush(Cel.InheritedStyle.ForeColor = System.Drawing.Color.Blue), new RectangleF((int)arrColumnLefts[iCount], (float)iTopMargin, (int)arrColumnWidths[iCount], (float)iCellHeight), strFormat);
//Drawing Cells Borders
e.Graphics.DrawRectangle(Pens.Red, new Rectangle((int)arrColumnLefts[iCount], iTopMargin, (int)arrColumnWidths[iCount], iCellHeight));
iCount++;
}
}
在：
void printDocument1_PrintPage(object sender, PrintPageEventArgs e)
{
try
{
//Set the left margin
int iLeftMargin = e.MarginBounds.Left, iTopMargin = e.MarginBounds.Top, iTmpWidth = 0;
//Whether more pages have to print or not
bool bMorePagesToPrint = false;
//For the first page to print set the cell width and header height
if (bFirstPage)
{
foreach (DataGridViewColumn GridCol in dataGridView1.Columns)
{
iTmpWidth = (int)(Math.Floor((double)((double)GridCol.Width / (double)iTotalWidth * (double)iTotalWidth * ((double)e.MarginBounds.Width / (double)iTotalWidth))));
iHeaderHeight = (int)(e.Graphics.MeasureString(GridCol.HeaderText, GridCol.InheritedStyle.Font, iTmpWidth).Height) + 11;
// Save width and height of headres
arrColumnLefts.Add(iLeftMargin);
arrColumnWidths.Add(iTmpWidth);
iLeftMargin += iTmpWidth;
}
}
//Loop till all the grid rows not get printed
while (iRow < dataGridView1.Rows.Count)
{
DataGridViewRow GridRow = dataGridView1.Rows[iRow];
//Set the cell height
iCellHeight = GridRow.Height + 5;
int iCount = 0;
//Check whether the current page settings allo more rows to print
if (iTopMargin + iCellHeight >= e.MarginBounds.Height + e.MarginBounds.Top)
{
bNewPage = true;
bFirstPage = false;
bMorePagesToPrint = true;
break;
}
else
{
if (bNewPage)
{
//Draw Header
e.Graphics.DrawString("Database Summary", new Font(dataGridView1.Font, FontStyle.Bold), Brushes.Black, e.MarginBounds.Left, e.MarginBounds.Top - e.Graphics.MeasureString("Database Summary", new Font(dataGridView1.Font, FontStyle.Bold), e.MarginBounds.Width).Height - 13);
String strDate = this.textBox4.Text;
//Draw Date
e.Graphics.DrawString(strDate, new Font(dataGridView1.Font, FontStyle.Regular), Brushes.Black, e.MarginBounds.Left + (e.MarginBounds.Width - e.Graphics.MeasureString(strDate, new Font(dataGridView1.Font, FontStyle.Regular), e.MarginBounds.Width).Width), e.MarginBounds.Top - e.Graphics.MeasureString("Database Summary", new Font(new Font(dataGridView1.Font, FontStyle.Regular), FontStyle.Regular), e.MarginBounds.Width).Height - 13);
//Draw Image
e.Graphics.DrawImage(pictureBox1.Image, new Rectangle((_screen.Width / 3) - 50, 0, this.pictureBox1.Size.Width, this.pictureBox1.Size.Height));
//Draw Columns
iTopMargin = e.MarginBounds.Top;
foreach (DataGridViewColumn GridCol in dataGridView1.Columns)
{
e.Graphics.FillRectangle(new SolidBrush(Color.Aqua), new Rectangle((int)arrColumnLefts[iCount], iTopMargin, (int)arrColumnWidths[iCount], iHeaderHeight));
e.Graphics.DrawRectangle(Pens.Black, new Rectangle((int)arrColumnLefts[iCount], iTopMargin, (int)arrColumnWidths[iCount], iHeaderHeight));
e.Graphics.DrawString(GridCol.HeaderText, GridCol.InheritedStyle.Font, new SolidBrush(GridCol.InheritedStyle.ForeColor), new RectangleF((int)arrColumnLefts[iCount], iTopMargin, (int)arrColumnWidths[iCount], iHeaderHeight), strFormat);
iCount++;
}
bNewPage = false;
iTopMargin += iHeaderHeight;
}
iCount = 0;
//Draw Columns Contents
foreach (DataGridViewCell Cel in GridRow.Cells)
{
if (Cel.Value != null)
{
e.Graphics.DrawString(Cel.Value.ToString(), Cel.InheritedStyle.Font, new SolidBrush(Cel.InheritedStyle.ForeColor = System.Drawing.Color.Blue), new RectangleF((int)arrColumnLefts[iCount], (float)iTopMargin, (int)arrColumnWidths[iCount], (float)iCellHeight), strFormat);
//Drawing Cells Borders
e.Graphics.DrawRectangle(Pens.Red, new Rectangle((int)arrColumnLefts[iCount], iTopMargin, (int)arrColumnWidths[iCount], iCellHeight));
iCount++;
}
}
}
iRow++;
iTopMargin += iCellHeight;
}
//If more lines exist, print another page.
if (bMorePagesToPrint)
{
e.HasMorePages = true;
}
else
{
e.HasMorePages = false;
}
}
catch (Exception exc)
{
SystemManager.ShowMessageBox("Message: " + exc.Message, "Error", 1);
}
}
以下是打印文件的完整代码：
int iCellHeight, iTotalWidth, iRow, iHeaderHeight = 0;
bool bFirstPage, bNewPage = false;
ArrayList arrColumnLefts, arrColumnWidths = new ArrayList();
void PrintPreview(object sender, EventArgs e)
{
PrintPreviewDialog printPreviewDialog = new PrintPreviewDialog();
printDocument1.DefaultPageSettings.Landscape = true;
printPreviewDialog.Document = printDocument1;
((Form)printPreviewDialog).WindowState = FormWindowState.Maximized;
printPreviewDialog.ShowDialog();
}
void PrintFile(object sender, EventArgs e)
{
PrintDialog printDialog = new PrintDialog();
printDocument1.DefaultPageSettings.Landscape = true;
printDialog.Document = printDocument1;
printDialog.UseEXDialog = true;
if (DialogResult.OK == printDialog.ShowDialog())
{
printDocument1.DocumentName = "Document Page Print";
printDocument1.Print();
}
}
void printDocument1_BeginPrint(object sender, PrintEventArgs e)
{
try
{
strFormat = new StringFormat();
strFormat.Alignment = StringAlignment.Center;
strFormat.LineAlignment = StringAlignment.Center;
strFormat.Trimming = StringTrimming.EllipsisCharacter;
arrColumnLefts.Clear();
arrColumnWidths.Clear();
iCellHeight = 0;
iRow = 0;
bFirstPage = true;
bNewPage = true;
iTotalWidth = 0;
foreach (DataGridViewColumn dgvGridCol in dataGridView1.Columns)
{
iTotalWidth += dgvGridCol.Width;
}
}
catch (Exception ex)
{
SystemManager.ShowMessageBox("Message: " + ex.Message, "Error", 1);
}
}
void printDocument1_PrintPage(object sender, PrintPageEventArgs e)
{
try
{
//Set the left margin
int iLeftMargin = e.MarginBounds.Left, iTopMargin = e.MarginBounds.Top, iTmpWidth = 0;
//Whether more pages have to print or not
bool bMorePagesToPrint = false;
//For the first page to print set the cell width and header height
if (bFirstPage)
{
foreach (DataGridViewColumn GridCol in dataGridView1.Columns)
{
iTmpWidth = (int)(Math.Floor((double)((double)GridCol.Width / (double)iTotalWidth * (double)iTotalWidth * ((double)e.MarginBounds.Width / (double)iTotalWidth))));
iHeaderHeight = (int)(e.Graphics.MeasureString(GridCol.HeaderText, GridCol.InheritedStyle.Font, iTmpWidth).Height) + 11;
// Save width and height of headres
arrColumnLefts.Add(iLeftMargin);
arrColumnWidths.Add(iTmpWidth);
iLeftMargin += iTmpWidth;
}
}
//Loop till all the grid rows not get printed
while (iRow < dataGridView1.Rows.Count)
{
DataGridViewRow GridRow = dataGridView1.Rows[iRow];
//Set the cell height
iCellHeight = GridRow.Height + 5;
int iCount = 0;
//Check whether the current page settings allo more rows to print
if (iTopMargin + iCellHeight >= e.MarginBounds.Height + e.MarginBounds.Top)
{
bNewPage = true;
bFirstPage = false;
bMorePagesToPrint = true;
break;
}
else
{
if (bNewPage)
{
//Draw Header
e.Graphics.DrawString("Database Summary", new Font(dataGridView1.Font, FontStyle.Bold), Brushes.Black, e.MarginBounds.Left, e.MarginBounds.Top - e.Graphics.MeasureString("Database Summary", new Font(dataGridView1.Font, FontStyle.Bold), e.MarginBounds.Width).Height - 13);
String strDate = this.textBox4.Text;
//Draw Date
e.Graphics.DrawString(strDate, new Font(dataGridView1.Font, FontStyle.Regular), Brushes.Black, e.MarginBounds.Left + (e.MarginBounds.Width - e.Graphics.MeasureString(strDate, new Font(dataGridView1.Font, FontStyle.Regular), e.MarginBounds.Width).Width), e.MarginBounds.Top - e.Graphics.MeasureString("Database Summary", new Font(new Font(dataGridView1.Font, FontStyle.Regular), FontStyle.Regular), e.MarginBounds.Width).Height - 13);
//Draw Image
e.Graphics.DrawImage(pictureBox1.Image, new Rectangle((_screen.Width / 3) - 50, 0, this.pictureBox1.Size.Width, this.pictureBox1.Size.Height));
//Draw Columns
iTopMargin = e.MarginBounds.Top;
foreach (DataGridViewColumn GridCol in dataGridView1.Columns)
{
e.Graphics.FillRectangle(new SolidBrush(Color.Aqua), new Rectangle((int)arrColumnLefts[iCount], iTopMargin, (int)arrColumnWidths[iCount], iHeaderHeight));
e.Graphics.DrawRectangle(Pens.Black, new Rectangle((int)arrColumnLefts[iCount], iTopMargin, (int)arrColumnWidths[iCount], iHeaderHeight));
e.Graphics.DrawString(GridCol.HeaderText, GridCol.InheritedStyle.Font, new SolidBrush(GridCol.InheritedStyle.ForeColor), new RectangleF((int)arrColumnLefts[iCount], iTopMargin, (int)arrColumnWidths[iCount], iHeaderHeight), strFormat);
iCount++;
}
bNewPage = false;
iTopMargin += iHeaderHeight;
}
iCount = 0;
//Draw Columns Contents
foreach (DataGridViewCell Cel in GridRow.Cells)
{
if (Cel.Value != null)
{
e.Graphics.DrawString(Cel.Value.ToString(), Cel.InheritedStyle.Font, new SolidBrush(Cel.InheritedStyle.ForeColor = System.Drawing.Color.Blue), new RectangleF((int)arrColumnLefts[iCount], (float)iTopMargin, (int)arrColumnWidths[iCount], (float)iCellHeight), strFormat);
//Drawing Cells Borders
e.Graphics.DrawRectangle(Pens.Red, new Rectangle((int)arrColumnLefts[iCount], iTopMargin, (int)arrColumnWidths[iCount], iCellHeight));
iCount++;
}
}
}
iRow++;
iTopMargin += iCellHeight;
}
//If more lines exist, print another page.
if (bMorePagesToPrint)
{
e.HasMorePages = true;
}
else
{
e.HasMorePages = false;
}
}
catch (Exception exc)
{
SystemManager.ShowMessageBox("Message: " + exc.Message, "Error", 1);
}
}
谢谢你们！
你的回答非常感谢！
答案 0 :(得分：3)
chanage
ArrayList arrColumnLefts, arrColumnWidths = new ArrayList();
到
ArrayList arrColumnLefts = new ArrayList();
ArrayList arrColumnWidths = new ArrayList();
OR
ArrayList arrColumnLefts = new ArrayList(), arrColumnWidths = new ArrayList();
<强>更新
ArrayList arrColumnLefts, arrColumnWidths = new ArrayList();
等于
ArrayList arrColumnLefts;
ArrayList arrColumnWidths = new ArrayList();
当你调用arrColumnLefts.Clear();时，你会得到null引用异常因为arrColumnLefts没有初始化。
答案 1 :(得分：1)
更改
ArrayList arrColumnLefts, arrColumnWidths = new ArrayList();
进入
ArrayList arrColumnLefts = new ArrayList();
ArrayList arrColumnWidths = new ArrayList();
第一行只初始化第二个arraylist