Retrieving JSON data from URL in Delphi XE7 - json

Question

I'm trying to get JSON data from an URL. The site I'm trying to connect is:
http://www.bitven.com/assets/js/rates.js
It contains the following JSON string:
{
"USD_TO_BSF_RATE": 112268.29,
"BTC_TO_USD_RATE": 13870.9,
"ETH_TO_USD_RATE": 752.222,
"BCH_TO_USD_RATE": 2960.81,
"LTC_TO_USD_RATE": 272.476,
"XRP_TO_USD_RATE": 1.01954,
"ETC_TO_USD_RATE": 31.1101,
"DASH_TO_USD_RATE": 1178.0,
"ZEC_TO_USD_RATE": 561.377,
"XMR_TO_USD_RATE": 354.709
}
I need to get the value of USD_TO_BSF_RATE, which is updated every 5 minutes in the site I mentioned. My code looks like:
uses
... System.JSON, IdHTTP;
function GetUrlContent(s: string): string;
var
IdHTTP1: TIdHTTP;
begin
IdHTTP1.Create;
GetUrlContent:=IdHTTP1.Get(s);
IdHTTP1.Destroy;
end;
procedure DolarUpdate;
var
json: string;
obj: TJSONObject;
url: string;
begin
try
json:=GetUrlContent('http://www.bitven.com/assets/js/rates.js');
try
obj := TJSONObject.ParseJSONValue(json) as TJSONObject;
TabbedForm.Edit2.Text := obj.Values['USD_TO_BSF_RATE'].Value;
finally
obj.Free;
end;
except
on E : Exception do
begin
ShowMessage('Error'+sLineBreak+E.ClassName+sLineBreak +E.Message);
end;
end;
end;
My app doesn't function correctly, nor return any messages. It only crashes.
What am I doing wrong?

Answer 1

Your GetUrlContent() function is not coded correctly. It needs to look like this instead:
function GetUrlContent(s: string): string;
var
IdHTTP1: TIdHTTP;
begin
IdHTTP1 := TIdHTTP.Create;
try
Result := IdHTTP1.Get(s);
finally
IdHTTP1.Free;
end;
end;
And your DolarUpdate() procedure should look more like this instead:
procedure DolarUpdate;
var
json: string;
obj: TJSONObject;
url: string;
begin
try
json := GetUrlContent('http://www.bitven.com/assets/js/rates.js');
obj := TJSONObject.ParseJSONValue(json) as TJSONObject;
if obj = nil then raise Exception.Create('Error parsing JSON');
try
TabbedForm.Edit2.Text := obj.Values['USD_TO_BSF_RATE'].Value;
finally
obj.Free;
end;
except
on E : Exception do
begin
ShowMessage('Error' + sLineBreak + E.ClassName + sLineBreak + E.Message);
end;
end;
end;