标签：client ini hang proc pass his customer value time
TField.CurValue Property
Represents the current value of the field component including changes made by other users of the database
Description
Use CurValue to examine the value of a field when a problem occurs while posting a value to the database using a provider. If the current field value causes a problem, such as a key violation, when posting the value, an event is generated to allow applications to respond to the problem. Provider components generate an OnUpdateError event. If a provider returns problem records to the client dataset, the client dataset generates an OnReconcileError event. In the OnUpdateError or OnReconcileError event handler, NewValue is the unposted value that caused the problem, OldValue is the value that was originally assigned to the field before any edits were made, and CurValue is the value that is currently assigned to the field. CurValue may differ from OldValue if another user changed the value of the field after OldValue was read.
Note: CurValue is only supported when the dataset is a TClientDataSet. In the provider‘s OnUpdateError event, a temporary client dataset containing fields with a CurValue property is passed to the event handler.
TField.NewValue Property
Represents the current value of the field component including pending cached updates.
Description
Use NewValue to examine or change the current value of a field when in the process of applying multiple updates. If the current field value is causing a problem, such as a key violation, when applying updates, datasets generate an OnUpdateError event. Similarly, provider components generate an OnUpdateError event when problems occur posting records from a client, and client datasets generate an OnReconcileError event when informed of problems by the provider. In the event handler, assign a new value to NewValue to correct the problem.
NewValue is the same as Value, except when errors are encountered while posting records. Setting NewValue in an OnUpdateError event handler, an OnUpdateRecord event handler, or an OnReconcileError event handler causes NewValue to differ from Value until the records have finished being applied to the underlying database table.
Note: The NewValue property is only usable when the data is accessed using a TClientDataSet component or cached updates is enabled
TField.OldValue Property
Represents the original value of the field (as a Variant).
Description
Read the OldValue property to examine or retrieve the original value of the field that was obtained from the dataset before any edits were posted. For example, in Delphi the following line replaces current pending changes with a field‘s original value:
Copy Code
NewValue :=OldValue;
Once records are applied successfully to the database, the old field value cannot be retrieved.
Note: the OldValue property is only usable when the data is accessed using a TClientDataSet component or cached updates is enabled
TField.Value Property
Represents the data in a field component.
Description
Use Value to read data directly from and write data directly to a field component at runtime. For example, use the Value property to affect the contents of a field that is not Visible.
Delphi Examples:
Copy Code
{
This example uses a button to copy the value of a field in
the previous record into the corresponding field in the
current record.
}
procedure TForm1.Button1Click(Sender: TObject);
var
SavePlace: TBookmark;
PrevValue: Variant;
begin
with Customers do
begin
{ get a bookmark so that we can return to the same record }
SavePlace := GetBookmark;
try
{ move to prior record}
FindPrior;
{ get the value }
PrevValue := FindField(‘Field2‘).Value;
{Move back to the bookmark
this may not be the next record anymore
if something else is changing the dataset asynchronously }
GotoBookmark(SavePlace);
{ Set the value }
Edit;
FindField(‘Field2‘).Value := PrevValue;
{ Free the bookmark }
finally
FreeBookmark(SavePlace);
end;
end;
end;
{
To ensure that the button is disabled when there is no
previous record, the OnDataChange event of the DataSource
detects when the user moves to the beginning of file (BOF
property becomes true), and disables the button. Detection
occurs on scrolling and editing, not selection with the mouse.
}
procedure TForm1.DS2DataChange(Sender: TObject; Field: TField);
begin
if Customers.Bof then
Button1.Enabled := False
else
Button1.Enabled := True;
end;
---------------------
标签：client ini hang proc pass his customer value time
原文地址：https://www.cnblogs.com/jijm123/p/10184298.html
