debugCheckHasMediaQuery function

bool debugCheckHasMediaQuery (BuildContext context)

Asserts that the given context has a MediaQuery ancestor.

Used by various widgets to make sure that they are only used in an appropriate context.

To invoke this function, use the following pattern, typically in the relevant Widget's build method:

assert(debugCheckHasMediaQuery(context));

Does nothing if asserts are disabled. Always returns true.

Implementation 

bool debugCheckHasMediaQuery(BuildContext context) {
  assert(() {
    if (context.widget is! MediaQuery && context.ancestorWidgetOfExactType(MediaQuery) == null) {
      final Element element = context;
      throw FlutterError(
        'No MediaQuery widget found.\n'
        '${context.widget.runtimeType} widgets require a MediaQuery widget ancestor.\n'
        'The specific widget that could not find a MediaQuery ancestor was:\n'
        '  ${context.widget}\n'
        'The ownership chain for the affected widget is:\n'
        '  ${element.debugGetCreatorChain(10)}\n'
        'Typically, the MediaQuery widget is introduced by the MaterialApp or '
        'WidgetsApp widget at the top of your application widget tree.'
      );
    }
    return true;
  }());
  return true;
}