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;

Open in new window

LVL 26
Eddie ShipmanAll-around developerAsked:
Who is Participating?

Improve company productivity with a Business Account.Sign Up

x
 
Geert GConnect With a Mentor Oracle 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 ...
0
 
Geert GOracle dbaCommented:
there is no exception handling here, just raising exceptions
no
try
except
end;

or am i missing something ?
0
 
Eddie ShipmanAll-around developerAuthor 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
Get your problem seen by more experts

Be seen. Boost your question’s priority for more expert views and faster solutions

 
Geert GOracle dbaCommented:
which exception is the one you want to see raised ?
and why ?
0
 
Geert GOracle dbaCommented:
maybe your assuming something, and i heard in a film once
assumptions are the mother of all f*ck*ps ...
0
 
Geert GOracle 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;

Open in new window

0
 
Eddie ShipmanAll-around developerAuthor Commented:
I already know where it goes.
0
 
Geert GOracle dbaCommented:
>> as expected, but then
this means you don't know why or are missing out on something or making an assumption ... ?
0
 
Eddie ShipmanAll-around developerAuthor 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 GOracle dbaCommented:
it shouldn't ...
0
 
Geert GOracle dbaCommented:
do you have more than 1 copy of the .pas file ?
0
 
Eddie ShipmanAll-around developerAuthor Commented:
nope.
0
 
Geert GOracle 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
 
Eddie ShipmanAll-around developerAuthor 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;

Open in new window

0
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

All Courses

From novice to tech pro — start learning today.