build method
Describes the part of the user interface represented by this widget.
The framework calls this method when this widget is inserted into the tree in a given BuildContext and when the dependencies of this widget change (e.g., an InheritedWidget referenced by this widget changes). This method can potentially be called in every frame and should not have any side effects beyond building a widget.
The framework replaces the subtree below this widget with the widget returned by this method, either by updating the existing subtree or by removing the subtree and inflating a new subtree, depending on whether the widget returned by this method can update the root of the existing subtree, as determined by calling Widget.canUpdate.
Typically implementations return a newly created constellation of widgets that are configured with information from this widget's constructor and from the given BuildContext.
The given BuildContext contains information about the location in the tree at which this widget is being built. For example, the context provides the set of inherited widgets for this location in the tree. A given widget might be built with multiple different BuildContext arguments over time if the widget is moved around the tree or if the widget is inserted into the tree in multiple places at once.
The implementation of this method must only depend on:
- the fields of the widget, which themselves must not change over time, and
- any ambient state obtained from the
contextusing BuildContext.dependOnInheritedWidgetOfExactType.
If a widget's build method is to depend on anything else, use a StatefulWidget instead.
See also:
- StatelessWidget, which contains the discussion on performance considerations.
Implementation
@override
Widget build(BuildContext context) {
/// CRITICAL: do not try to retrieve DartBlockEditorInheritedWidget here.
/// Reason: when re-ordering statements, the inherited widget does not appear to be retrievable during the drag, causing a null error to be thrown.
/// Explanation: when a drag gesture is stared, the widget starts "floating", essentially leaving its original parent widget. As such, it loses the context of its parent who holds the DartBlockEditorInheritedWidget.
/// Solution: only access the inherited widget in parent widgets which cannot be re-ordered,e.g., the CustomFunctionWidget.
// final dartBlockEditorInheritedWidget = DartBlockEditorInheritedWidget.of(context);
return Card(
child: Padding(
padding: const EdgeInsets.only(left: 4, right: 4, bottom: 8),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
mainAxisSize: MainAxisSize.min,
children: [
// Title and execution order number
Row(
children: [
Container(
padding: const EdgeInsets.all(8),
decoration: BoxDecoration(
color: Theme.of(context).colorScheme.primary,
shape: BoxShape.circle,
),
child: Text(
"1",
style: TextStyle(
color: Theme.of(context).colorScheme.onPrimary,
fontWeight: FontWeight.bold,
),
),
),
const SizedBox(width: 8),
Text(
"Initialize Loop Variable",
style: Theme.of(context).textTheme.titleMedium,
),
],
),
// Initialization statement
Padding(
padding: const EdgeInsets.only(left: 32),
child: statement.initStatement != null
? StatementWidget(
statement: statement.initStatement!,
includeBottomPadding: false,
showLabel: false,
canChange: canChange,
canDelete: canDelete,
canReorder: false,
canDuplicate: false,
onChanged: (value) {
statement.initStatement = value;
onChanged(statement);
},
onDelete: () {
statement.initStatement = null;
onChanged(statement);
},
onCopyStatement: (statementToCopy, cut) {
onCopiedStatement(statementToCopy, cut);
if (cut) {
statement.initStatement = null;
onChanged(statement);
}
},
onCopiedStatement: onCopiedStatement,
onPastedStatement: onPastedStatement,
onPasteStatement: (statementToPaste) {
if (statementToPaste.statementType ==
StatementType.variableDeclarationStatement) {
statement.initStatement = statementToPaste.copy();
onPastedStatement();
onChanged(statement);
} else {
ScaffoldMessenger.of(context).showSnackBar(
createDartBlockInfoSnackBar(
context,
iconData: Icons.error,
message:
"Can only use 'Declare Variable' statement for initialization.",
backgroundColor: Theme.of(
context,
).colorScheme.errorContainer,
color: Theme.of(
context,
).colorScheme.onErrorContainer,
),
);
}
},
onDuplicate: (_) {
// The initialization statement cannot be duplicated.
},
onAppendNewStatement: null,
customFunctions: customFunctions,
)
: TextButton.icon(
onPressed: canChange
? () {
final dartBlockInheritedWidget =
DartBlockEditorInheritedWidget.of(context);
final programTree = dartBlockInheritedWidget
.program
.buildTree();
final existingVariableDefinitions = programTree
.findVariableDefinitions(
statement.hashCode,
includeNode: false,
);
StatementEditor.create(
statementType:
StatementType.variableDeclarationStatement,
existingVariableDefinitions:
existingVariableDefinitions,
customFunctions: dartBlockInheritedWidget
.program
.customFunctions,
onSaved: (value) {
Navigator.of(context).pop();
statement.initStatement = value;
onChanged(statement);
},
).showAsModalBottomSheet(context);
}
: null,
icon: const Icon(Icons.add),
label: const Text("Add 'Declare Variable' statement"),
),
),
const SizedBox(height: 16),
// Condition with step number 2
Row(
children: [
Container(
padding: const EdgeInsets.all(8),
decoration: BoxDecoration(
color: Theme.of(context).colorScheme.primary,
shape: BoxShape.circle,
),
child: Text(
"2",
style: TextStyle(
color: Theme.of(context).colorScheme.onPrimary,
fontWeight: FontWeight.bold,
),
),
),
const SizedBox(width: 8),
Text(
"Check Condition",
style: Theme.of(context).textTheme.titleMedium,
),
const SizedBox(width: 8),
Tooltip(
message:
"If the condition is false, exit the loop.\nIf the condition is true, continue to step 3.",
child: InkWell(
borderRadius: BorderRadius.circular(12),
onTap: () {
showDialog(
context: context,
builder: (context) => AlertDialog(
title: Text("Step 2: Check Condition"),
content: Text(
"If the condition is false, exit the loop.\nIf the condition is true, continue to step 3.",
),
actions: <Widget>[
TextButton(
child: const Text('Okay'),
onPressed: () {
Navigator.of(context).pop();
},
),
],
),
);
},
child: Icon(Icons.info_outline),
),
),
],
),
// Decision visualization
Padding(
padding: const EdgeInsets.only(left: 32.0),
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: [
// Condition expression
LayoutBuilder(
builder: (context, constraints) {
return SingleChildScrollView(
scrollDirection: Axis.horizontal,
child: ConstrainedBox(
constraints: BoxConstraints(
minWidth: constraints.maxWidth,
),
child: DartBlockValueWidget(
value: statement.condition,
borderRadius: BorderRadius.circular(12),
),
),
);
},
),
// Alternative approach: (slightly more performant, but requires manual calculation of padding)
// SizedBox(
// width: double.infinity,
// child: SingleChildScrollView(
// scrollDirection: Axis.horizontal,
// child: Container(
// constraints: BoxConstraints(
// minWidth:
// MediaQuery.of(context).size.width -
// 72 -
// 32, // Account for paddings
// ),
// child: DartBlockValueWidget(
// value: statement.condition,
// borderRadius: BorderRadius.circular(12),
// ),
// ),
// ),
// ),
const SizedBox(height: 8),
// Decision arrows
Row(
children: [
Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Row(
children: [
const Icon(
Icons.check,
size: 16,
color: Colors.green,
),
const SizedBox(width: 4),
Text(
"If true:",
style: Theme.of(context).textTheme.bodySmall
?.copyWith(
color: Colors.green,
fontWeight: FontWeight.bold,
),
),
const SizedBox(width: 4),
Text(
"continue to step 3",
style: Theme.of(context).textTheme.bodySmall,
),
],
),
const SizedBox(height: 4),
Row(
children: [
const Icon(
Icons.close,
size: 16,
color: Colors.red,
),
const SizedBox(width: 4),
Text(
"Else:",
style: Theme.of(context).textTheme.bodySmall
?.copyWith(
color: Colors.red,
fontWeight: FontWeight.bold,
),
),
const SizedBox(width: 4),
Text(
"exit the loop",
style: Theme.of(context).textTheme.bodySmall,
),
const SizedBox(width: 4),
const Icon(Icons.exit_to_app, size: 16),
],
),
],
),
],
),
],
),
),
const SizedBox(height: 16),
// Loop body with step number 3
Row(
children: [
Container(
padding: const EdgeInsets.all(8),
decoration: BoxDecoration(
color: Theme.of(context).colorScheme.primary,
shape: BoxShape.circle,
),
child: Text(
"3",
style: TextStyle(
color: Theme.of(context).colorScheme.onPrimary,
fontWeight: FontWeight.bold,
),
),
),
const SizedBox(width: 8),
Text(
"Execute Loop Body",
style: Theme.of(context).textTheme.titleMedium,
),
],
),
// Loop body statements
Padding(
padding: const EdgeInsets.only(left: 32.0),
child: StatementListView(
neoTechCoreNodeKey: statement.bodyStatements.isNotEmpty
? statement.bodyStatements.last.hashCode
: (statement.initStatement?.hashCode ?? statement.hashCode),
statements: statement.bodyStatements,
canDelete: canDelete,
canChange: canChange,
canReorder: canReorder,
onCopiedStatement: onCopiedStatement,
onChanged: (statements) {
statement.bodyStatements = statements;
onChanged(statement);
},
onDuplicate: (index) {
final duplicatedStatement = statement.bodyStatements[index]
.copy();
if (index < statement.bodyStatements.length - 1) {
statement.bodyStatements.insert(
index + 1,
duplicatedStatement,
);
} else {
statement.bodyStatements.add(duplicatedStatement);
}
onChanged(statement);
},
onPastedStatement: onPastedStatement,
customFunctions: customFunctions,
),
),
const SizedBox(height: 16),
// Update step with number 4
Row(
children: [
Container(
padding: const EdgeInsets.all(8),
decoration: BoxDecoration(
color: Theme.of(context).colorScheme.primary,
shape: BoxShape.circle,
),
child: Text(
"4",
style: TextStyle(
color: Theme.of(context).colorScheme.onPrimary,
fontWeight: FontWeight.bold,
),
),
),
const SizedBox(width: 8),
Text(
"Update Loop Variable",
style: Theme.of(context).textTheme.titleMedium,
),
const SizedBox(width: 8),
Tooltip(
message:
"After executing the loop body, this step updates the loop variable before checking the condition again.",
child: InkWell(
borderRadius: BorderRadius.circular(12),
onTap: () {
showDialog(
context: context,
builder: (context) => AlertDialog(
title: Text("Step 4: Update Loop Variable"),
content: Text(
"After executing the loop body, this step updates the loop variable before checking the condition again.",
),
actions: <Widget>[
TextButton(
child: const Text('Okay'),
onPressed: () {
Navigator.of(context).pop();
},
),
],
),
);
},
child: Icon(Icons.info_outline),
),
),
],
),
// Update statement
Padding(
padding: const EdgeInsets.only(left: 32),
child: statement.postStatement != null
? StatementWidget(
statement: statement.postStatement!,
includeBottomPadding: false,
showLabel: false,
canChange: canChange,
canDelete: canDelete,
canReorder: canReorder,
canDuplicate: false,
onChanged: (value) {
statement.postStatement = value;
onChanged(statement);
},
onDelete: () {
statement.postStatement = null;
onChanged(statement);
},
onCopyStatement: (statementToCopy, cut) {
onCopiedStatement(statementToCopy, cut);
if (cut) {
statement.postStatement = null;
onChanged(statement);
}
},
onCopiedStatement: onCopiedStatement,
onDuplicate: (statementToDuplicate) {
/// Cannot duplicate this statement.
},
onPastedStatement: onPastedStatement,
onPasteStatement: (statementToPaste) {
if (statementToPaste.statementType ==
StatementType.variableAssignmentStatement) {
statement.postStatement = statementToPaste.copy();
onPastedStatement();
onChanged(statement);
} else {
// Special case: the for-loop's init ('post-step') can only be a 'Update Variable' type statement.
ScaffoldMessenger.of(context).showSnackBar(
createDartBlockInfoSnackBar(
context,
iconData: Icons.error,
message:
"Can only use 'Update Variable' statement for a For-Loop's post-step.",
backgroundColor: Theme.of(
context,
).colorScheme.errorContainer,
color: Theme.of(
context,
).colorScheme.onErrorContainer,
),
);
}
},
onAppendNewStatement: null,
customFunctions: customFunctions,
)
: TextButton.icon(
onPressed: canChange
? () {
final dartBlockEditorInheritedWidget =
DartBlockEditorInheritedWidget.of(context);
final programTree = dartBlockEditorInheritedWidget
.program
.buildTree();
final existingVariableDefinitions = programTree
.findVariableDefinitions(
statement.initStatement?.hashCode ??
statement.hashCode,
includeNode: true,
);
StatementEditor.create(
statementType:
StatementType.variableAssignmentStatement,
existingVariableDefinitions:
existingVariableDefinitions,
customFunctions: dartBlockEditorInheritedWidget
.program
.customFunctions,
onSaved: (value) {
Navigator.of(context).pop();
statement.postStatement = value;
onChanged(statement);
},
).showAsModalBottomSheet(context);
}
: null,
icon: const Icon(Icons.add),
label: const Text("Add 'Update Variable' statement"),
),
),
// Visual flow indicator showing that it goes back to step 2
Padding(
padding: const EdgeInsets.only(left: 16.0, top: 8.0),
child: Row(
children: [
const Icon(Icons.replay, size: 20),
const SizedBox(width: 8),
Text(
"Return to step 2",
style: Theme.of(context).textTheme.bodySmall?.copyWith(
fontStyle: FontStyle.italic,
),
),
],
),
),
],
),
),
);
}