delphi - Could not convert variant of type (Null) into type (OleStr) - Stack Overflow
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Do you know why the block of code bellow will negate the "Could not convert variant of type (Null) into type (OleStr)" on some computers, not all of them but 3 out of ten computers generate the error message.
function GetWMIstringSW(const WMIClass, WMIProperty:string):
wbemFlagForwardOnly = $;
FWbemObjectSet: OLEV
FWbemObject
Result:='';
FWbemObjectSet:= FWMIService.ExecQuery(Format('Select %s from %s',[WMIProperty, WMIClass]),'WQL',wbemFlagForwardOnly);
:= IUnknown(FWbemObjectSet._NewEnum) as IEnumV
while oEnum.Next(1, FWbemObject, iValue) = 0 do
if not VarIsNull(FWbemObject.Properties_.Item(WMIProperty).Value) then
Result:=FWbemObject.Properties_.Item(WMIProperty).V
LNode := ClientForm.TreeView1.Items.AddChild(Node, Format('%s',[String(FWbemObject.Name)]));
LNode2 := ClientForm.TreeView1.Items.AddChild(LNode, Format('%s',[String(FWbemObject.Version)]));
FWbemObject:=U
The function is then executed at FormCreate:
GETWMIstringSW('Win32_Product','Name');
Thank you so much for your help.
You code fails when the value of a WMI property returns null. You can fix this, checking if the property has a null value before to cast or convert to an string. For this task you can use the
function or just use the
method to safely convert variants to strings like so.
LNode := ClientForm.TreeView1.Items.AddChild(Node,
Format('%s',[VarToStr(FWbemObject.Name)]));
LNode2 := ClientForm.TreeView1.Items.AddChild(LNode,
Format('%s',[VarToStr(FWbemObject.Version)]));
113k11253398
If you want to null variants to be automatically converted to empty strings, 0 integers, or false booleans, set NullStrictConvert (unit System.Variants) to true.
4,370113067
To avoid the error message do
NullStrictConvert := // avoid NULL OLE conversion error
Sometimes, the FWbemObject
is not NULL
but an exception is raise :
"Can'nt convert an Array of Variant in OleStr "
As exemple :
the BiosVersion (is an array)
To solve it, try this :
for I := VarArrayLowBound(FWbemObject.BIOSVersion, 1) to
VarArrayHighBound(FWbemObject.BIOSVersion, 1) do
L.Add( VarToStr(FWbemObject.BIOSVersion[i]) );
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delphi could not convert variant of type (null) into type (olestr)procedure TForm3.DBEdit1Change(Se
delphi could not convert variant of type (null) into type (olestr)procedure&TForm3.DBEdit1Change(Sender:&TObject);&//onchange事件vari:s:xcom:beginfor&i&:=&2&to&20&dobegins:='edit'+inttostr(i);xcom:=findcomponent(s);if&xcom&&nil&thenbeginTedit(xcom).Text:=ADOquery1.Fields[i-2].V&//break&按了之后这一条被选中了。错了么？procedure&TForm3.FormShow(Sender:&TObject);beginADOConnection1.Connected:=&//连接，设置。ADOConnection1.Connected:=ADOQuery1.Connection:=adoconnection1;ADOQuery1.SQL.CADOQuery1.CADOQuery1.SQL.Text:='select&CustomerID,pyCode,CustomerName,ProvinceID,CityID,Address,Zip,Phone,Fax,Email,HomePage,Industry,Type,Source,Status,Revenue,employees,owner,StockNo,Notes&from&customers';ADOQuery1.ODataSource1.DataSet:=adoquery1;ADOtable1.CADOtable1.Connection:=ADOConnection1;&//连接adotable后做的事情ADOtable1.tablename:='customers';ADOtable1.Odbnavigator1.DataSource:=DataSource1;dbgrid1.DataSource:=DataSource1;edit1.Text:='';f();&//外观设置的函数调用procedure&TForm3.ToolButton5Click(Sender:&TObject);&//刷新按钮beginadoquery1.Cadoquery1.Of();我能写的都写了，但是刷新按钮还是错，错误提示如题。我什么都不做，运行先按刷新还是出现同样的错误。我不知道我sql语句哪里被修改了？
[解决办法]Tedit(xcom).Text:=ADOquery1.Fields[i-2].V&//break&按了之后这一条被选中了。错了么？Tedit(xcom).Text:=ADOquery1.Fields[i-2].//用这个确保是文本你的错误代码没有贴出来，你的F函数有问题。}