XML Namespace in Delphi

问题

I am trying to access some Nodes in my XML File, but I cant get it working because i probably don't understand XML-Namepsaces in Delphi.

<gesmes:Envelope xmlns:gesmes="http://www.gesmes.org/xml/2002-08-01" xmlns="http://www.ecb.int/vocabulary/2002-08-01/eurofxref">
    <gesmes:subject>Reference rates</gesmes:subject>
    <gesmes:Sender>
        <gesmes:name>European Central Bank</gesmes:name>
    </gesmes:Sender>
    <Cube>
        <Cube time="2018-01-18">
            <Cube currency="USD" rate="1.2235"/>
            <Cube currency="JPY" rate="136.07"/>
            <Cube currency="BGN" rate="1.9558"/>
            <Cube currency="CZK" rate="25.365"/>
            <Cube currency="DKK" rate="7.4475"/>
            <Cube currency="GBP" rate="0.88208"/>
            <Cube currency="HUF" rate="308.51"/>
            <Cube currency="PLN" rate="4.1665"/>
            <Cube currency="RON" rate="4.6480"/>
            <Cube currency="SEK" rate="9.8305"/>
            <Cube currency="CHF" rate="1.1748"/>
            <Cube currency="NOK" rate="9.6013"/>
            <Cube currency="HRK" rate="7.4409"/>
            <Cube currency="RUB" rate="69.2126"/>
            <Cube currency="TRY" rate="4.6374"/>
            <Cube currency="AUD" rate="1.5311"/>
            <Cube currency="BRL" rate="3.9321"/>
            <Cube currency="CAD" rate="1.5229"/>
            <Cube currency="CNY" rate="7.8582"/>
            <Cube currency="HKD" rate="9.5648"/>
            <Cube currency="IDR" rate="16325.38"/>
            <Cube currency="ILS" rate="4.1950"/>
            <Cube currency="INR" rate="78.1210"/>
            <Cube currency="KRW" rate="1306.61"/>
            <Cube currency="MXN" rate="22.8174"/>
            <Cube currency="MYR" rate="4.8396"/>
            <Cube currency="NZD" rate="1.6759"/>
            <Cube currency="PHP" rate="62.068"/>
            <Cube currency="SGD" rate="1.6175"/>
            <Cube currency="THB" rate="39.054"/>
            <Cube currency="ZAR" rate="15.0035"/>
        </Cube>
    </Cube>
</gesmes:Envelope>

I tried to access the Cube Nodes like that:

procedure TForm2.Button1Click(Sender: TObject);
var
  Doc: IXMLDocument;
  Node: IXMLNode;
  sl: TStringList;
begin
  Doc := LoadXMLDocument('C:\Users\Kevin\Desktop\test.xml');
  node := Doc.DocumentElement;

  ShowMessage(Node.ChildNodes['Cube']);
end;

I realized that my output is: "gesmes:Cube". I don't think that is right... I excpected to get the the first "Cube" Node. I am not sure how namespaces in Delphi work so it would be great if i could get some help here.

Best Regards!

回答1:

You are passing an IXMLNode interface pointer to ShowMessage(), which expects a string instead. So presumably, in your real code, you have actually done ShowMessage(Node.ChildNodes['Cube'].NodeName); instead.

Which indeed reports 'gesmes:Cube', which is not what you are expecting. The Cube you want is in the http://www.ecb.int/vocabulary/2002-08-01/eurofxref namespace, which is different than the namespace of its parent Envelope (http://www.gesmes.org/xml/2002-08-01). So what actually happens is that DocumentElement.ChildNodes['Cube'] tries to find a Cube in the Envelope's namespace, finds no such element, so TXMLDocument creates a new one because the doNodeAutoCreate flag is enabled by default in the Doc.Options property. That is the Cube that DocumentElement.ChildNodes['Cube'] returns, not the Cube you want.

Because the Envelope and its immediate Cube child are in different namespaces, you can't use ChildNodes['Cube'] on the DocumentElement, you have to use ChildNodes.FindNode() instead, specifying the Cube's actual namespace:

Node := Doc.DocumentElement;
Node := Node.ChildNodes.FindNode('Cube', 'http://www.ecb.int/vocabulary/2002-08-01/eurofxref');

The next Cube is in the same namespace as its parent Cube, so you can use ChildNodes['Cube'] to get it:

Node := Node.ChildNodes['Cube'];

Then you can access the time attribute, if needed:

Node.Attributes['time']

And loop through the remaining child Cubes:

Node := Node.ChildNodes.First;
while Node <> nil do
begin
  if Node.LocalName = 'Cube' then
  begin
    // use Node.Attributes['currency'] and Node.Attributes['rate'] as needed...
  end;
  Node := Node.NextSibling;
end;

Here is the complete code:

procedure TForm2.Button1Click(Sender: TObject);
var
  Doc: IXMLDocument;
  Node: IXMLNode;
  sl: TStringList;
begin
  sl := TStringList.Create;
  try
    Doc := LoadXMLDocument('C:\Users\Kevin\Desktop\test.xml');
    try
      Node := Doc.DocumentElement;
      if Node = nil then ... // handle the error as needed...

      Node := Node.ChildNodes.FindNode('Cube', 'http://www.ecb.int/vocabulary/2002-08-01/eurofxref');
      if Node = nil then ... // handle the error as needed...

      Node := Node.ChildNodes['Cube'];
      if Node = nil then ... // handle the error as needed...

      Node := Node.ChildNodes.First;
      while Node <> nil do
      begin
        if Node.LocalName = 'Cube' then
          sl.Add(Node.Attributes['currency'] + '=' + Node.Attributes['rate']);
        Node := Node.NextSibling;
      end;
    finally
      Node := nil;
      Doc := nil;
    end;

    // use sl as needed...

  finally
    sl.Free;
  end;
end;

来源：https://stackoverflow.com/questions/48343141/xml-namespace-in-delphi

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xml

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namespaces