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Re-work exception handling

Can somebody rework the exception handling in this code. I can't quite get it right...

RSSXML and RSSXML2 are IXMLDOMDocumetn2 instances created earlier in the code and used in ParseFeed
to parse out the info.

What is happening is that the first exception is being raised because RSSXML.documentElement is going to be nil. It goes into the finally, as expected, but then when tracing, it goes back to this line:
  oMainChannelNode := RSSXML.SelectSingleNode('rss').FirstChild;

procedure TRSSFrame.GetFeed;
var
  oChannelNode:     IXMLDOMNode;
  oMainChannelNode: IXMLDOMNode;
  oItemNodes:       IXMLDOMNodeList;
  i:                Integer;
begin
  SL := TStringList.Create;
  try
    SL.Text := FHTTP.Get('http://www.our-site.com/blog/?cat='+sCat1No+'&feed=rss2');
    // Deliberately setting SL.Text = '' to check exception handling
    SL.Text := '';
    RSSXML.loadXML(SL.Text);
    if not Assigned(RSSXML.documentElement) then
      raise EXMLLoadingException.CreateFmt('RSS Feed for Category %s did not load properly.', [sCat1]);
 
    oMainChannelNode := RSSXML.SelectSingleNode('rss').FirstChild;
    if Assigned(oMainChannelNode) then
    begin
      SL.Clear;
      if sCat2No <> '' then
      begin
        SL.Text := FHTTP.Get('http://www.our-site.com/blog/?cat='+sCat2No+'&feed=rss2');
        RSSXML2.loadXML(SL.Text);
        if not Assigned(RSSXML2.documentElement) then
          raise EXMLLoadingException.CreateFmt('RSS Feed for Category %s did not load properly.', [sCat2]);
 
        oChannelNode := RSSXML2.SelectSingleNode('rss').FirstChild;
        oItemNodes   := oChannelNode.selectNodes('//item');
        for i := 0 to oItemNodes.Length-1 do
          oMainChannelNode.appendChild(oItemNodes.item[i]);
      end;
      SL.Clear;
      if sCat3No <> '' then
      begin
        SL.Text := FHTTP.Get('http://www.our-site.com/blog/?cat='+sCat3No+'&feed=rss2');
        RSSXML2.loadXML(SL.Text);
        if not Assigned(RSSXML2.documentElement) then
          raise EXMLLoadingException.CreateFmt('RSS Feed for Category %s did not load properly.', [sCat3]);
 
        oChannelNode := RSSXML2.SelectSingleNode('rss').FirstChild;
        oItemNodes   := oChannelNode.selectNodes('//item');
        for i := 0 to oItemNodes.Length-1 do
          oMainChannelNode.appendChild(oItemNodes.item[i]);
      end;
    end;
  finally
    SL.Free;
    ParseFeed; // This parses the XML in the RSSXML document
  end; //try
end;

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EddieShipman
Asked:
EddieShipman
  • 9
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1 Solution
 
Geert GruwezOracle dbaCommented:
there is no exception handling here, just raising exceptions
no
try
except
end;

or am i missing something ?
0
 
EddieShipmanAuthor Commented:
Well, could you rework it?
I'm having a whale of a time getting it correct and the posted code is not working correctly.
0
 
Geert GruwezOracle dbaCommented:
which exception is the one you want to see raised ?
and why ?
0
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Geert GruwezOracle dbaCommented:
maybe your assuming something, and i heard in a film once
assumptions are the mother of all f*ck*ps ...
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Geert GruwezOracle dbaCommented:
to see where it jumps out as a last resort i usually add a identifier and some logging
and a wrapping try finally with showing the log

this way you can trace where the function goes
every level should have a different letter, to see if it actually goes into that level
procedure TRSSFrame.GetFeed;
var 
  M, Msg: string; 
  X: Integer;
  procedure Jump(aMsg: string = '');
  begin
    if aMsg <> '' then 
      M := aMsg; 
    Inc(X);
    Msg := Msg + M + IntToStr(X) + #13#1O;
  end;
var
  oChannelNode:     IXMLDOMNode;
  oMainChannelNode: IXMLDOMNode;
  oItemNodes:       IXMLDOMNodeList;
  i:                Integer;
begin
  X := 0;
  Msg := '';
  try
    SL := TStringList.Create;
    try
      Jump('A');
      SL.Text := FHTTP.Get('http://www.our-site.com/blog/?cat='+sCat1No+'&feed=rss2');
      Jump;
      // Deliberately setting SL.Text = '' to check exception handling
      SL.Text := '';
      Jump;
      RSSXML.loadXML(SL.Text);
      Jump;
      if not Assigned(RSSXML.documentElement) then
        raise EXMLLoadingException.CreateFmt('RSS Feed for Category %s did not load properly.', [sCat1]);
      Jump;    
      oMainChannelNode := RSSXML.SelectSingleNode('rss').FirstChild;
      Jump;
      if Assigned(oMainChannelNode) then
      begin
        Jump('B');
        SL.Clear;
        Jump;
        if sCat2No <> '' then
        begin
          Jump('C');
          SL.Text := FHTTP.Get('http://www.our-site.com/blog/?cat='+sCat2No+'&feed=rss2');
          Jump;
          RSSXML2.loadXML(SL.Text);
          Jump;
          if not Assigned(RSSXML2.documentElement) then
            raise EXMLLoadingException.CreateFmt('RSS Feed for Category %s did not load properly.', [sCat2]);
          Jump;
          oChannelNode := RSSXML2.SelectSingleNode('rss').FirstChild;
          Jump;
          oItemNodes   := oChannelNode.selectNodes('//item');
          Jump;
          for i := 0 to oItemNodes.Length-1 do
            oMainChannelNode.appendChild(oItemNodes.item[i]);
          Jump;
        end;
        Jump;
        SL.Clear;
        Jump;
        if sCat3No <> '' then
        begin
          Jump('D'); 
          SL.Text := FHTTP.Get('http://www.our-site.com/blog/?cat='+sCat3No+'&feed=rss2');
          Jump;
          RSSXML2.loadXML(SL.Text);
          Jump;
          if not Assigned(RSSXML2.documentElement) then
            raise EXMLLoadingException.CreateFmt('RSS Feed for Category %s did not load properly.', [sCat3]);
          Jump;   
          oChannelNode := RSSXML2.SelectSingleNode('rss').FirstChild;
          Jump;
          oItemNodes   := oChannelNode.selectNodes('//item');
          Jump;
          for i := 0 to oItemNodes.Length-1 do
            oMainChannelNode.appendChild(oItemNodes.item[i]);
          Jump;
        end;
      end;
    finally
      Jump('E');
      SL.Free;
      Jump;
      ParseFeed; 
      Jump;// This parses the XML in the RSSXML document
    end; //try
  finally
    Jump('F');
    ShowMessage(Msg);
  end;
end;

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EddieShipmanAuthor Commented:
I already know where it goes.
0
 
Geert GruwezOracle dbaCommented:
>> as expected, but then
this means you don't know why or are missing out on something or making an assumption ... ?
0
 
EddieShipmanAuthor Commented:
I understand that it is supposed to go into the finally after the exception is raised, (AS EXPECTED)
But then why it goes BACK to the next line, I don't understand that.
0
 
Geert GruwezOracle dbaCommented:
it shouldn't ...
0
 
Geert GruwezOracle dbaCommented:
do you have more than 1 copy of the .pas file ?
0
 
EddieShipmanAuthor Commented:
nope.
0
 
Geert GruwezOracle dbaCommented:
why this :
finally
    SL.Free;
    ParseFeed; // This parses the XML in the RSSXML document
  end; //try
end;

and not, (if you raised an exception, you still want to run ParseFeed ???)
  finally
    SL.Free;
  end; //try
  ParseFeed; // This parses the XML in the RSSXML document
end;
0
 
EddieShipmanAuthor Commented:
We've kind of worked it out like that.

procedure TAccuBuildRSSFrame.GetFeed;
var
  oChannelNode:     IXMLDOMNode;
  oRSSNode:         IXMLDOMNode;
  oMainChannelNode: IXMLDOMNode;
  oItemNodes:       IXMLDOMNodeList;
  i:                Integer;
  bParse:           Boolean;
begin
  LockWindowUpdate(RSSPanel.Handle);
  SL := TStringList.Create;
  bParse := False;
  try
    try
      SL.Text := FHTTP.Get('http://www.our-site.com/blog/?cat='+sCat1No+'&feed=rss2');
      RSSXML.loadXML(SL.Text);
      oRSSNode := RSSXML.SelectSingleNode('rss');
      oMainChannelNode := oRSSNode.FirstChild;
      if Assigned(oMainChannelNode) then
      begin
        SL.Clear;
        if sCat2No <> '' then
        begin
          SL.Text := FHTTP.Get('http://www.our-site.com/blog/?cat='+sCat2No+'&feed=rss2');
          RSSXML2.loadXML(SL.Text);
          oRSSNode := RSSXML2.SelectSingleNode('rss');
          oChannelNode := oRSSNode.FirstChild;
          if Assigned(oChannelNode) then
          begin
            oItemNodes   := oChannelNode.selectNodes('//item');
            for i := 0 to oItemNodes.Length-1 do
              oMainChannelNode.appendChild(oItemNodes.item[i]);
            bParse := True;
          end;
        end;
        SL.Clear;
        if sCat3No <> '' then
        begin
          SL.Text := FHTTP.Get('http://www.our-site.com/blog/?cat='+sCat3No+'&feed=rss2');
          RSSXML2.loadXML(SL.Text);
          oRSSNode := RSSXML2.SelectSingleNode('rss');
          oChannelNode := oRSSNode.FirstChild;
          if Assigned(oChannelNode) then
          begin
            oItemNodes   := oChannelNode.selectNodes('//item');
            for i := 0 to oItemNodes.Length-1 do
              oMainChannelNode.appendChild(oItemNodes.item[i]);
            bParse := True;
          end;
        end;
      end;
    except
      on e:Exception do
      begin
        ShowMessage('There was a problem loading the RSS Feed.');
        bParse := False;
      end;
    end;
  finally
    SL.Free;
    oChannelNode     := nil;
    oRSSNode         := nil;
    oMainChannelNode := nil;
    oItemNodes       := nil;
  end; //try
  if bParse then
    ParseFeed;
end;

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Geert GruwezOracle dbaCommented:
it's not normal for a finally to jump back into the code .
i'm boggled at this.

i had this some times when creating a copy of the file,
opening an old file, and then compiling.
Because the current directory was looking at the old file, the old file got compiled.

that's why i asked if you had any duplicates ...

but this is something very suspiciously buggy ...
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