Lazarus Reading XML- with TXMLDocument and TXPathVariable

也就是使用XPath的方式，具体语法规则查看http://www.w3school.com.cn/xpath/xpath_syntax.asp，说明得相当详细。这里列举例子是说明在Lazarus/FPC下具体应用于实现，以及注意事项。首先可以构建一个“ReadXPath”的函数方便调用。毕竟每次使用EvaluateXPathExpression后还有些任务要处理……。

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function ReadXPath(const aNode: TDOMNode; const aPath: string): TDOMNode;

var

rv: TXPathVariable;

tl: TFPList;

begin

Result := nil;

if Assigned(aNode) then

begin

rv := EvaluateXPathExpression(aPath, aNode);

if Assigned(rv) then

begin

tl := rv.AsNodeSet;

if Assigned(tl) then

begin

if tl.Count > 0 then

begin

Result := TDOMNode(tl[0]);

end;

end;

end;

end;

end;

具体使用了，要记住返回的其实是“元素”，就算强制约定了“属性”——[@Attrib],所以要读取任何值，都要按“扫描到元素”的方式来处理。

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function ReadCFG: boolean;

var

.....

vConfigXml: string = '';

HistoryPath: string = '';

TracePath: string = '';

vXP: TDOMNode;

.....

begin

Result := False;

ReadXMLFile(xmlCfg, vConfigXml);

vXP := ReadXPath(xmlCfg, '/Config/HistoryPath[@value]');

if Assigned(vXP) then

begin

if vXP.HasAttributes then

HistoryPath := vXP.Attributes.Item[0].NodeValue;

end;

vXP := ReadXPath(xmlCfg, '/Config/TracePath[@value]');

if Assigned(vXP) then

begin

if vXP.HasAttributes then

TracePath := vXP.Attributes.Item[0].NodeValue;

end;

if (HistoryPath <> '') and (TracePath <> '') then

.....

end;