Flutter: How do you make a card clickable?

Flutter use composition over properties. Wrap the desired widget into a clickable one to achieve what you need.

Some clickable widgets : GestureDetector, InkWell, InkResponse.

GestureDetector(
  onTap: () => ......,
  child: Card(...),
);

Flutter provides the InkWell Widget. by registering a callback you can decide what happens when user clicks on the card (called tap in flutter). InkWell also implements Material Design ripple effect

Card(
  child: new InkWell(
    onTap: () {
      print("tapped");
    },
    child: Container(
      width: 100.0,
      height: 100.0,
    ),
  ),
),

I think you can also use InkWell apart from GestureDetector just wrap the card inside InkWell() Widget

InkWell(
  onTap: (){ print("Card Clicked"); }
  child: new Card(),
);

You can use Inkwell and insert splashColor which, at the click of the user, creates the rebound effect with the chosen color, on the card .. This is mainly used in material design.

return Card(
  color: item.completed ? Colors.white70 : Colors.white,
  elevation: 8,
  child: InkWell(
      splashColor: "Insert color when user tap on card",
      onTap: () async {

      },
    ),
);

In Flutter, InkWell is a material widget that responds to touch action.

InkWell(
    child: Card(......),
    onTap: () { 
        print("Click event on Container"); 
    },
);

GestureDetector is a widget that detects the gestures.

GestureDetector(
    onTap: () { 
        print("Click event on Container"); 
    },
    child: Card(.......),
)

Difference

InkWell is a material widget and it can show you a Ripple Effect whenever a touch was received.

GestureDetector is more general-purpose, not only for touch but also for other gestures.