Object::connect: No such slot

[kango]

it has to be

connect(ui->horizontalSlider, SIGNAL(valueChanged(int)),this, SLOT(counterChanged(int)));
connect(ui->ResetButton,SIGNAL(clicked()), this, SLOT(SetSliderValue()));
connect(ui->PlayButton,SIGNAL(clicked()), this, SLOT(animate()));

connect(ui->horizontalSlider, SIGNAL(valueChanged(int)),this, SLOT(counterChanged(int)));
connect(ui->ResetButton,SIGNAL(clicked()), this, SLOT(SetSliderValue()));
connect(ui->PlayButton,SIGNAL(clicked()), this, SLOT(animate()));

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If i replace with "this", how do they know which object the slots belong to?