更新 Flutter ListTile 与水龙头不工作

Question

The goal is to change the values in the ListTile of leading and subtitle to null on tap. The tap is switching the _act boolean, but the ListTile's leading: and subtitle: values do not change from their initial state. My code for the ListView is below. Please help.

        return new ListView(
          children: querySnapShot.data.documents.map((DocumentSnapshot document) {
            bool _act = false;
            return new ListTile(
              leading: _act != false ? const Icon(Icons.remove_red_eye, color: Color(0xff00caff), size: 40) : null,
              title: new Text((DBProvider.db.idDeHasher(document['exampleid'], key) ?? 'fallback'), style: TextStyle(color: secondaryColor)),
              subtitle: _act != false ? new Text((document['exampleString']  ?? 'fallbackString'), style: TextStyle(color: secondaryColor)) : null,
              onTap: () { 
                _act = !_act;
                print(_act.toString());
                }
            );
          }).toList(),
        );

Answer 1

You need to make your widget a Stateful Widget and call setState when there is a tap on the ListTile .

According to the docs :

Calling setState notifies the framework that the internal state of this object has changed in a way that might impact the user interface in this subtree, which causes the framework to schedule a build for this State object.

So if the state of the widget changes you have to call setState to trigger a rebuild of the view and see immediatly the changes implied by the new state.

I added a demo using your code as an example:

     // define a list of acts
        List _acts = [];
         return new ListView(
          children: querySnapShot.data.documents.asMap().entries.map((entry) {
          // declare all entries of the list to false
          acts.add(false);
          // access the index 
          int index = entry.key;
          // access the document
          DocumentSnapshot document = entry.value;
          // DocumentSnapshot document = entry
            return new ListTile(
              leading: _acts[index] != false ? const Icon(Icons.remove_red_eye, color: Color(0xff00caff), size: 40) : null,
              title: new Text((DBProvider.db.idDeHasher(entry.val['exampleid'], key) ?? 'fallback'), style: TextStyle(color: secondaryColor)),
              subtitle: _acts[index] != false ? new Text((document['exampleString']  ?? 'fallbackString'), style: TextStyle(color: secondaryColor)) : null,
              onTap: () { 
               // call setstate
              setState(() { // new line
              // change the bool variable based on the index
               _acts[index] = !_acts[index];
                print(_acts[index].toString());
              });
                }
            );
          }).toList(),
        );

Answer 2

onTap: () { 
setState((){
                _act = !_act;
                print(_act.toString());
                }
});

Just copy and paste this, it will work.

Answer 3

replace bool _act = false; just below

class _SomeClass extends State<SomeClass> { and surround with setState({});