我正在尝试优化我的过慢的DataGridView,它使用SQLite数据库通过虚拟模式和缓存获取数据,我已经使用了Double Buffering的技巧,并删除了列和行的自动大小。但是,尽管阅读此内容:
http://msdn.microsoft.com/en-us/library/ha5xt0d9.aspx
然后 :
http://msdn.microsoft.com/en-us/library/ha5xt0d9.aspx
我的网格非常慢,实际上对数据库的查询非常快,但是即使已经通过缓存加载了数据,DataGridView的绘制也非常慢...
但是也许我的Cache类不好,所以我想知道我做错了什么。原理很简单,缓存分为3个部分:上,当前(也可以称为“中间”和“下”),每个部分都由索引(开始和结束)定界,如果已经加载了数据,则缓存将给出根据那些非常简单的规则得出的值:
如果值在当前部分中没问题,只需加载数据
如果需要的值是高位还是低位,则此部分成为当前部分不会有问题,只需要一个新部分。
即
上部分:0-100
当前部分:101-201
下部:202-302
需要的值在下部,没有问题,电流变低,上部变成电流,只需要重新加载新的下部。显然,如果所需的值具有缓存不可用的行索引,则会重新加载该行索引。
public class Cache
{
private Dictionary<PagePart, Page> _pages;
public Dictionary<PagePart, Page> Pages
{
get { return this._pages; }
set { this._pages = value; }
}
private String _tableName;
public String TableName
{
get { return this._tableName; }
set { this._tableName = value; }
}
private SQLiteConnection _connection;
public SQLiteConnection Connection
{
get { return this._connection; }
set { this._connection = value; }
}
public Cache(String tableName, SQLiteConnection connection)
{
this.Connection = connection;
this.TableName = tableName;
this.Pages = new Dictionary<PagePart, Page>(PageNumber);
IndexRange indexRangeUpper = new IndexRange(0, PageSize);
IndexRange indexRangeCurrent = new IndexRange(PageSize + 1, 2 * PageSize);
IndexRange indexRangeLower = new IndexRange(2 * PageSize + 1, 3 * PageSize);
DataTable dataTableUpper = this.GetDataTableFromTable(indexRangeUpper);
DataTable dataTableCurrent = this.GetDataTableFromTable(indexRangeCurrent);
DataTable dataTableLower = this.GetDataTableFromTable(indexRangeLower);
Page pageUpper = new Page(indexRangeUpper, dataTableUpper);
Page pageCurrent = new Page(indexRangeCurrent, dataTableCurrent);
Page pageLower = new Page(indexRangeLower, dataTableLower);
Pages.Add(PagePart.Upper, pageUpper);
Pages.Add(PagePart.Current, pageCurrent);
Pages.Add(PagePart.Lower, pageLower);
}
private IndexRange GetTableIndexRange()
{
String commandText = String.Format("SELECT MAX(RowId) FROM {0}", this.TableName);
SQLiteCommand command = new SQLiteCommand(commandText, this.Connection);
this.Connection.Open();
command.CommandText = commandText;
String maxRowIdString = command.ExecuteScalar().ToString();
this.Connection.Close();
Int32 maxRowId = Int32.Parse(maxRowIdString);
return new IndexRange(0, maxRowId);
}
public Object GetCellValue(Int32 rowIndex, Int32 columnIndex)
{
Int32 indexLowerStart = Pages[PagePart.Lower].Range.StartIndex;
Int32 indexLowerEnd = Pages[PagePart.Lower].Range.EndIndex;
Int32 indexCurrentStart = Pages[PagePart.Current].Range.StartIndex;
Int32 indexCurrentEnd = Pages[PagePart.Current].Range.EndIndex;
Int32 indexUpperStart = Pages[PagePart.Upper].Range.StartIndex;
Int32 indexUpperEnd = Pages[PagePart.Upper].Range.EndIndex;
IndexRange indexRangeTable = this.GetTableIndexRange();
Int32 indexTableStart = indexRangeTable.StartIndex;
Int32 indexTableEnd = indexRangeTable.EndIndex;
// Using the cache...
if ((indexUpperStart <= rowIndex) && (rowIndex <= indexLowerEnd))
{
if ((indexLowerStart <= rowIndex) && (rowIndex <= indexLowerEnd))
{
if (indexTableEnd > indexLowerEnd)
{
this.Pages[PagePart.Upper] = this.Pages[PagePart.Current];
this.Pages[PagePart.Current] = this.Pages[PagePart.Lower];
IndexRange indexRangeLower = new IndexRange(this.Pages[PagePart.Current].Range.EndIndex + 1, this.Pages[PagePart.Current].Range.EndIndex + PageSize);
DataTable dataTableLower = this.GetDataTableFromTable(indexRangeLower);
Page pageLower = new Page(indexRangeLower, dataTableLower);
this.Pages[PagePart.Lower] = pageLower;
Int32 pageSize = this.Pages[PagePart.Current].Data.Rows.Count;
return this.Pages[PagePart.Current].Data.Rows[rowIndex % pageSize][columnIndex];
}
else
{
Int32 pageSize = this.Pages[PagePart.Lower].Data.Rows.Count;
return this.Pages[PagePart.Lower].Data.Rows[rowIndex % pageSize][columnIndex];
}
}
if ((indexCurrentStart <= rowIndex) && (rowIndex <= indexCurrentEnd))
{
Int32 pageSize = this.Pages[PagePart.Current].Data.Rows.Count;
return this.Pages[PagePart.Current].Data.Rows[rowIndex % pageSize][columnIndex];
}
if ((indexUpperStart <= rowIndex) && (rowIndex <= indexUpperEnd))
{
if (indexTableStart < indexUpperStart)
{
this.Pages[PagePart.Lower] = this.Pages[PagePart.Current];
this.Pages[PagePart.Current] = this.Pages[PagePart.Upper];
IndexRange indexRangeUpper = new IndexRange(this.Pages[PagePart.Current].Range.StartIndex - 1, this.Pages[PagePart.Current].Range.EndIndex - PageSize);
DataTable dataTableUpper = this.GetDataTableFromTable(indexRangeUpper);
Page pageUpper = new Page(indexRangeUpper, dataTableUpper);
this.Pages[PagePart.Upper] = pageUpper;
Int32 pageSize = this.Pages[PagePart.Current].Data.Rows.Count;
return this.Pages[PagePart.Current].Data.Rows[rowIndex % pageSize][columnIndex];
}
else
{
Int32 pageSize = this.Pages[PagePart.Upper].Data.Rows.Count;
return this.Pages[PagePart.Upper].Data.Rows[rowIndex % pageSize][columnIndex];
}
}
return null;
}
// Need to reload the cache...
else
{
IndexRange indexRangeCurrent = new IndexRange(rowIndex - (PageSize / 2), rowIndex + (PageSize / 2));
IndexRange indexRangeLower = new IndexRange(indexRangeCurrent.EndIndex + 1, indexRangeCurrent.EndIndex + PageSize);
IndexRange indexRangeUpper = new IndexRange(indexRangeCurrent.StartIndex - 1, indexRangeCurrent.StartIndex - PageSize );
DataTable dataTableUpper = this.GetDataTableFromTable(indexRangeUpper);
DataTable dataTableCurrent = this.GetDataTableFromTable(indexRangeCurrent);
DataTable dataTableLower = this.GetDataTableFromTable(indexRangeLower);
Page pageUpper = new Page(indexRangeUpper, dataTableUpper);
Page pageCurrent = new Page(indexRangeCurrent, dataTableCurrent);
Page pageLower = new Page(indexRangeLower, dataTableLower);
Pages[PagePart.Upper] = pageUpper;
Pages[PagePart.Current] = pageCurrent;
Pages[PagePart.Lower] = pageLower;
Int32 pageSize = this.Pages[PagePart.Current].Data.Rows.Count;
return this.Pages[PagePart.Current].Data.Rows[rowIndex % pageSize][columnIndex];
}
}
private DataTable GetDataTableFromTable(IndexRange indexRange)
{
if (this.Connection != null)
{
String commandText = String.Format("SELECT * FROM {0} WHERE RowId BETWEEN {1} AND {2}", this.TableName, indexRange.StartIndex, indexRange.EndIndex);
SQLiteCommand command = new SQLiteCommand(commandText, this.Connection);
SQLiteDataAdapter dataAdapter = new SQLiteDataAdapter(command);
DataTable dataTable = new DataTable(this.TableName, this.TableName);
dataAdapter.Fill(dataTable);
return dataTable;
}
else
{
return null;
}
}
private const Int32 PageNumber = 3;
private const Int32 PageSize = 128;
public class Page
{
public Page(IndexRange range, DataTable data)
{
this.Range = range;
this.Data = data;
}
private IndexRange _range;
public IndexRange Range
{
get { return this._range; }
set { this._range = value; }
}
private DataTable _data;
public DataTable Data
{
get { return this._data; }
set { this._data = value; }
}
}
public enum PagePart
{
Upper,
Current,
Lower,
}
public class IndexRange
{
private Int32 _startIndex;
public Int32 StartIndex
{
get { return this._startIndex; }
set { this._startIndex = value; }
}
private Int32 _endIndex;
public Int32 EndIndex
{
get { return this._endIndex; }
set { this._endIndex = value; }
}
public IndexRange(Int32 startIndex, Int32 stopIndex)
{
this.StartIndex = startIndex;
this.EndIndex = stopIndex;
}
}
}
但是天哪...这幅画太慢了...我该怎么办...?
最佳答案
这是回答我自己的问题的一种方法,我只是使用主键来避免对偏移量的混淆,无论是向上滚动还是向下滚动(是的,这都是惰性的,所以这不是...高效,但不仅仅是不使用缓存也可以)完全简单易用[例如,不使用3个缓存,但最终只有一个缓存可以正常完成工作]):
public class Cache
{
protected SQLiteConnection Connection { get; set; }
protected String TableName { get; set; }
protected const Int32 PageSize = 512;
protected CachePage PageCurrent { get; set; }
protected IndexRange IndexRangeTable { get; set; }
public Cache(SQLiteConnection connection, String tableName)
{
SQLiteConnection.ClearAllPools();
this.Connection = connection;
this.TableName = tableName;
IndexRange indexRangeCurrent = new IndexRange(0, PageSize - 1);
DataTable dataTableCurrent = this.GetDataTableFromTable(indexRangeCurrent);
this.PageCurrent = new CachePage(indexRangeCurrent, dataTableCurrent);
}
public Object GetCellValue(Int32 rowIndex, Int32 columnIndex)
{
DataRow dataRowFound = this.PageCurrent.Data.Rows.Find(rowIndex);
if (dataRowFound != null)
{
return dataRowFound[columnIndex];
}
else
{
this.ShiftPageToIndex(rowIndex);
return GetCellValue(rowIndex, columnIndex);
}
}
private void ShiftPageToIndex(Int32 index)
{
this.PageCurrent.Range.Start = index;
this.PageCurrent.Range.Stop = index + PageSize;
this.PageCurrent.Data = this.GetDataTableFromTable(this.PageCurrent.Range);
this.PageCurrent.Range.Start = index;
this.PageCurrent.Range.Stop = index + this.PageCurrent.Data.Rows.Count;
}
private IndexRange GetTableIndexRange()
{
String commandText = String.Format("SELECT MAX(RowId) FROM {0}", this.TableName);
SQLiteCommand command = new SQLiteCommand(commandText, this.Connection);
this.Connection.Open();
command.CommandText = commandText;
String maxRowIdString = command.ExecuteScalar().ToString();
this.Connection.Close();
Int32 maxRowId = Int32.Parse(maxRowIdString);
return new IndexRange(0, maxRowId);
}
private DataTable GetDataTableFromTable(IndexRange indexRange)
{
if (this.Connection != null)
{
String commandText = String.Format("SELECT * FROM {0} WHERE RowId BETWEEN {1} AND {2}", this.TableName, indexRange.Start, indexRange.Stop);
SQLiteCommand command = new SQLiteCommand(commandText, this.Connection);
SQLiteDataAdapter dataAdapter = new SQLiteDataAdapter(command);
DataTable dataTable = new DataTable(this.TableName, this.TableName);
dataAdapter.Fill(dataTable);
dataTable.Columns.Add("RowId", typeof(Int64));
for (Int32 i = 0; i < dataTable.Rows.Count; i++)
{
dataTable.Rows[i]["RowId"] = i + indexRange.Start;
}
dataTable.PrimaryKey = new DataColumn[] { dataTable.Columns["Rowid"] };
return dataTable;
}
else
{
return null;
}
}
}
public class CachePage
{
public CachePage(IndexRange range, DataTable data)
{
this.Range = range;
this.Data = data;
}
public IndexRange Range {get; set;}
public DataTable Data {get; set;}
}
public class IndexRange
{
public Int32 Start {get; set;}
public Int32 Stop { get; set; }
public IndexRange(Int32 start, Int32 stop)
{
this.Start = start;
this.Stop = stop;
}
}
//如何从虚拟DataGridView调用它?
private void dataGridViewMain_CellValueNeeded(Object sender, DataGridViewCellValueEventArgs e)
{
if (this.Cache != null)
{
e.Value = this.Cache.GetCellValue(e.RowIndex, e.ColumnIndex);
}
}
因此,它非常酷,而且无需大惊小怪,也无需考虑太多...
此代码段可用于使用RowId字段而不是Primary Key(实际上不是真正的字段)来创建SQLite数据库表查看器。
另一个更好的解决方案是按... asc或desc顺序获取数据,然后使用模运算符查找此类数据,但是我对于这个任务太懒了。我猜想SQLite dll仍然比使用预先存在的DataColumn作为PrimaryKey更快地获得数据顺序...但是正如我所说的,我现在很懒。