User:Nhollm
Warning: All of this is subject to change. Do NOT use it until its finished. For any Questions or Input write me an E-Mail ich@nhollm.de or write me at the forums 'nhollm'.
Todo: (TObjectDictionary)
TDictionary
TDictionary is a generic Data-Container for Key-value pairs (associative array).
It was introduced with Generics.Collections in FPC 3.2.0 (June 2020). It's part of the FPC Runtime Library and fully Delphi compatible.
Basic syntax (FPC)
{$mode objfpc}
program Example;
uses
Generics.Collections; //import the generics-library of the RTL
type
TStrStrDictionary = specialize TDictionary<string, string>; //specialize a new dictionary-object and set the desired data-type of key and value
var
MyDictionary : TStrStrDictionary;
begin
MyDictionary := TStrStrDictionary.Create;
try
//do stuff with your dictionary..
finally
MyDictionary.Free;
end;
end.
Usage:
Add
Add Entry or update its current value (key, value)
MyDictionary.AddOrSetValue('Key1', 'Value1');
The function AddOrSetValue is recommended.
Alternatively there is the Function Add().
Add() will throw an error if the Key already exists: 'Dublicate Not Allowed in Dictionary'.
If you only want to add new Items and not overwrite them in the case they exist, take a look at TryAdd() below. It provides a feedback too.
Remove
MyDictionary.Remove('Key2');
If the Key does not exist, no Error is thrown.
Clear
MyDictionary.Clear;
Get Value
WriteLn(MyDictionary.Items['Key1']);
If the provided key does not exist, this will throw an Error: 'Dictionary Key does not Exist'. You can use 'TryGetValue' instead.
Item Count
Total number of Items in dictionary (count)
WriteLn('Items in Dictionary: ' + IntToStr(MyDictionary.Count));
Loops
//Loop Keys
for KeyStr in MyDictionary.Keys do
WriteLn('Found key:' + KeyStr);
//Loop Values
for ValueStr in MyDictionary.Values do
WriteLn('Found Value: ' + ValueStr);
//Loop Key-Value-Pairs
//var KeyValuePair : TStrStrDictionary.TDictionaryPair;
for KeyValuePair in MyDictionary do
WriteLn('Found a Pair: Key:' + KeyValuePair.Key + ' Value:' + KeyValuePair.Value);
Check If Key/Value Exists
//Check if Key exists
if MyDictionary.ContainsKey('Key1') then
WriteLn('key exists')
else
WriteLn('key not found');
//Check if Value exists
if MyDictionary.ContainsValue('Searched value') then
writeln('value exists')
else
writeln('value not found');
Trying
If you want to get a feedback, use these functions. They return a boolean.
True if sucessfull, False if not. No Error is thrown, so they are a good alternative to GetValue or Add.
TryAdd
if MyDictionary.TryAdd('Key','TestValue') then
writeln('added successfully')
else
writeln('not sucessfull');
TryAdd does not update an existing keys value. Use AddOrSetValue instead. (Even tho there is no feedback provided)
TryGetValue
TryGetValue takes two Arguments ->(key, value) and returns a boolean.
If found, it returns True and the provided 'value' variable becomes the value.
If not found, the function returns False and the provided 'value'-variable is nil.
if MyDictionary.TryGetValue('Key', SearchedValue) then
WriteLn('Key found. Its value is: ' + SearchedValue)
else
WriteLn('Could not get value');
//writeln(BoolToStr(MyDictionary.TryGetValue('Key', SearchedValue)));
ToArray
Returns an Array of type 'TDictionaryPair'.
//var myArray : array of TStrStrDictionary.TDictionaryPair;
myArray := MyDictionary.ToArray()
//WriteLn(length(myArray));
//WriteLn(myArray[0].Key)
//WriteLn(myArray[0].Value)
Event Notifications
You can set up custom Functions/Procedures which are triggered if an Key or Value got added/removed.
To do this, we add 2 procedures to the class we specialize from TDictionary.
The TDictionary class provides the in-build functions 'OnKeyNotify' and 'OnValueNotify'. Now we assign them to our procedures.
(Hint: If you update a existing value, there is no "updated"Event. Instead "removed" followed by "added" is triggered.)
TODO: get the Key Name inside the ValueNotify-Event kontext
{$mode objfpc}
program Example;
uses
Generics.Collections;
type
TStrStrDictionary = Class(Specialize TDictionary<String,String>)
private
procedure DoKeyNotify(ASender: TObject;constref AItem: ShortString; AAction: TCollectionNotification);
procedure DoValueNotify(ASender: TObject;constref AItem: ShortString; AAction: TCollectionNotification);
end;
procedure TStrStrDictionary.DoKeyNotify(ASender: TObject;constref AItem: ShortString; AAction: TCollectionNotification);
begin
//WriteLn(AAction);//AAction can be 'cnRemoved' or 'cnAdded'
if AAction = cnAdded then
writeln('A Key got added, the Key is:', AItem)
else if AAction = cnRemoved then
writeln('A Key got removed, the Key was:', AItem)
end;
procedure TStrStrDictionary.DoValueNotify(ASender: TObject;constref AItem: ShortString; AAction: TCollectionNotification);
begin
Writeln(AAction);//can be cnRemoved or cnAdded
if AAction = cnAdded then
writeln('A Value got added, the value is:', AItem)
else if AAction = cnRemoved then
writeln('A Value got removed, the value was:', AItem)
end;
var
MyDictionary : TStrStrDictionary;
TestArr : array of TStrStrDictionary.TDictionaryPair;
begin
MyDictionary := TStrStrDictionary.Create;
//Event notifications:
MyDictionary.OnKeyNotify:=@MyDictionary.DoKeyNotify;
MyDictionary.OnValueNotify:=@MyDictionary.DoValueNotify;
try
MyDictionary.AddOrSetValue('Key1', 'Value1');//triggers Add Event
MyDictionary.AddOrSetValue('Key1', 'New Value');//triggers Add and Remove Event
MyDictionary.Remove('Key1');//triggers Remove Event
readln();
finally
MyDictionary.Free;
end;
end.
Exceptions
To handle Exceptions, import the SysUtils Library.
{$mode objfpc}
program Example;
uses
Generics.Collections,SysUtils;
type
TStrStrDictionary = specialize TDictionary<string, string>;
var
MyDictionary : TStrStrDictionary;
begin
MyDictionary := TStrStrDictionary.Create;
try
try
WriteLn(MyDictionary.Items['KeyXY']); // Accessing a non existing key
except
on E: Exception do begin
WriteLn('An exception was raised: ' + E.Message);
WriteLn(E.ClassName);
end;
end;
ReadLn();
finally
MyDictionary.Free;
end;
end.
//Output: An exception was raised: Dictionary key does not exist
//EListError
Delphi
{$mode delphi}
uses generics.collections;
type TStrIntDict = TDictionary<string,integer>;
var
MyDict : TStrIntDict;
begin
MyDict:=TStrIntDict.create;
MyDict.AddorSetValue('foo',42);
if MyDict.ContainsKey('foo') then
WriteLn(MyDict['foo']);
end.