Updates selection controls gallery demo (#3225)

examples/material_gallery/lib/demo/selection_controls_demo.dart

@@ -4,74 +4,244 @@
 
 import 'package:flutter/material.dart';
 
+import '../gallery/demo.dart';
+
+const String _checkboxText =
+  "# Checkboxes\n"
+  "Checkboxes allow the user to select multiple options from a set.";
+
+const String _checkboxCode =
+"""// Member variable holding the checkbox's value.
+bool checkboxValue = false;
+
+// Create a checkbox.
+new Checkbox(
+  value: checkboxValue,
+  onChanged: (bool value) {
+    setState(() {
+      checkboxValue = value;
+    }
+  );
+})
+
+// Create a disabled checkbox.
+// Checkboxes are disabled when onChanged isn't
+// specified or null.
+new Checkbox(value: false)""";
+
+const String _radioText =
+  "# Radio buttons\n"
+  "Radio buttons allow the user to select one option from a set. Use radio "
+  "buttons for exclusive selection if you think that the user needs to see "
+  "all available options side-by-side.";
+
+const String _radioCode =
+"""// Member variable holding value.
+int radioValue = 0;
+
+// Method setting value.
+void handleRadioValueChanged(int value) {
+  setState(() {
+    radioValue = value;
+  });
+}
+
+// Creates a set of radio buttons.
+new Row(
+  children: <Widget>[
+    new Radio<int>(
+      value: 0,
+      groupValue: radioValue,
+      onChanged: handleRadioValueChanged
+    ),
+    new Radio<int>(
+      value: 1,
+      groupValue: radioValue,
+      onChanged: handleRadioValueChanged
+    ),
+    new Radio<int>(
+      value: 2,
+      groupValue: radioValue,
+      onChanged: handleRadioValueChanged
+    )
+  ]
+);
+
+// Creates a disabled radio button.
+new Radio<int>(
+  value: 0,
+  groupValue: 0
+);""";
+
+const String _switchText =
+  "# Switches\n"
+  "On/off switches toggle the state of a single settings option. The option "
+  "that the switch controls, as well as the state it’s in, should be made "
+  "clear from the corresponding inline label.";
+
+const String _switchCode =
+"""// Member variable holding value.
+bool switchValue = false;
+
+// Create a switch.
+new Switch(
+  value: switchValue,
+  onChanged: (bool value) {
+    setState(() {
+      switchValue = value;
+    }
+  );
+})
+
+// Create a disabled switch.
+// Switches are disabled when onChanged isn't
+// specified or null.
+new Switch(value: false)""";
+
 class SelectionControlsDemo extends StatefulWidget {
   @override
   _SelectionControlsDemoState createState() => new _SelectionControlsDemoState();
 }
 
 class _SelectionControlsDemoState extends State<SelectionControlsDemo> {
-  bool _checkboxValue = false;
-  int _radioValue = 0;
-  bool _switchValue = false;
+  @override
+  Widget build(BuildContext context) {
+    List<ComponentDemoTabData> demos = <ComponentDemoTabData>[
+      new ComponentDemoTabData(
+        tabName: "CHECKBOX",
+        description: _checkboxText,
+        widget: buildCheckbox(),
+        exampleCode: _checkboxCode
+      ),
+      new ComponentDemoTabData(
+        tabName: "RADIO",
+        description: _radioText,
+        widget: buildRadio(),
+        exampleCode: _radioCode
+      ),
+      new ComponentDemoTabData(
+        tabName: "SWITCH",
+        description: _switchText,
+        widget: buildSwitch(),
+        exampleCode: _switchCode
+      )
+    ];
 
-  void _setCheckboxValue(bool value) {
-    setState(() {
-      _checkboxValue = value;
-    });
+    return new TabbedComponentDemoScaffold(
+      title: 'Selection Controls',
+      demos: demos
+    );
   }
 
-  void _setRadioValue(int value) {
-    setState(() {
-      _radioValue = value;
-    });
-  }
+  bool checkboxValueA = true;
+  bool checkboxValueB = false;
+  int radioValue = 0;
+  bool switchValue = false;
 
-  void _setSwitchValue(bool value) {
+  void handleRadioValueChanged(int value) {
     setState(() {
-      _switchValue = value;
+      radioValue = value;
     });
   }
 
-  @override
-  Widget build(BuildContext context) {
-    return new Scaffold(
-      appBar: new AppBar(title: new Text('Selection controls')),
-      body: new Column(
+  Widget buildCheckbox() {
+    return new Align(
+      alignment: new FractionalOffset(0.5, 0.4),
+      child: new Column(
+        mainAxisAlignment: MainAxisAlignment.collapse,
         children: <Widget>[
           new Row(
+            mainAxisAlignment: MainAxisAlignment.collapse,
             children: <Widget>[
-              new Checkbox(value: _checkboxValue, onChanged: _setCheckboxValue),
-              new Checkbox(value: false), // Disabled
-              new Checkbox(value: true), // Disabled
-            ],
-            mainAxisAlignment: MainAxisAlignment.spaceAround
+              new Checkbox(value: checkboxValueA, onChanged: (bool value) {
+                setState(() {
+                  checkboxValueA = value;
+                });
+              }),
+              new Checkbox(value: checkboxValueB, onChanged: (bool value) {
+                setState(() {
+                  checkboxValueB = value;
+                });
+              })
+            ]
           ),
           new Row(
-            children: <int>[0, 1, 2].map((int i) {
-              return new Radio<int>(
-                value: i,
-                groupValue: _radioValue,
-                onChanged: _setRadioValue
-              );
-            }).toList(),
-            mainAxisAlignment: MainAxisAlignment.spaceAround
-          ),
+            mainAxisAlignment: MainAxisAlignment.collapse,
+            children: <Widget>[
+              // Disabled checkboxes
+              new Checkbox(value: true),
+              new Checkbox(value: false)
+            ]
+          )
+        ]
+      )
+    );
+  }
+
+  Widget buildRadio() {
+    return new Align(
+      alignment: new FractionalOffset(0.5, 0.4),
+      child: new Column(
+        mainAxisAlignment: MainAxisAlignment.collapse,
+        children: <Widget>[
           new Row(
-            children: <int>[0, 1].map((int i) {
-              return new Radio<int>(value: i, groupValue: 0); // Disabled
-            }).toList(),
-            mainAxisAlignment: MainAxisAlignment.spaceAround
+            mainAxisAlignment: MainAxisAlignment.collapse,
+            children: <Widget>[
+              new Radio<int>(
+                value: 0,
+                groupValue: radioValue,
+                onChanged: handleRadioValueChanged
+              ),
+              new Radio<int>(
+                value: 1,
+                groupValue: radioValue,
+                onChanged: handleRadioValueChanged
+              ),
+              new Radio<int>(
+                value: 2,
+                groupValue: radioValue,
+                onChanged: handleRadioValueChanged
+              )
+            ]
           ),
+          // Disabled radio buttons
           new Row(
+            mainAxisAlignment: MainAxisAlignment.collapse,
             children: <Widget>[
-              new Switch(value: _switchValue, onChanged: _setSwitchValue),
-              new Switch(value: false), // Disabled
-              new Switch(value: true), // Disabled
-            ],
-            mainAxisAlignment: MainAxisAlignment.spaceAround
-          ),
-        ],
-        mainAxisAlignment: MainAxisAlignment.spaceAround
+              new Radio<int>(
+                value: 0,
+                groupValue: 0
+              ),
+              new Radio<int>(
+                value: 1,
+                groupValue: 0
+              ),
+              new Radio<int>(
+                value: 2,
+                groupValue: 0
+              )
+            ]
+          )
+        ]
+      )
+    );
+  }
+
+  Widget buildSwitch() {
+    return new Align(
+      alignment: new FractionalOffset(0.5, 0.4),
+      child: new Row(
+        mainAxisAlignment: MainAxisAlignment.collapse,
+        children: <Widget>[
+          new Switch(value: switchValue, onChanged: (bool value) {
+            setState(() {
+              switchValue = value;
+            });
+          }),
+          // Disabled switches
+          new Switch(value: true),
+          new Switch(value: false)
+        ]
       )
     );
   }