小编Joh*_*yan的帖子

使用package:flutter_test，我可以创建一个查找器，通过键查找小部件：

expect(find.byKey(const ValueKey('counter')), findsOneWidget);

或通过文字：

expect(find.text('0'), findsOneWidget);

我还可以找到从此小部件衍生的小部件：

expect(
  find.descendant(
    of: find.byKey(const ValueKey('counter')),
    matching: find.text('0'),
  ),
  findsNothing,
);

或者祖先：

expect(
  find.ancestor(
    of: find.text('0'),
    matching: find.byKey(const ValueKey('counter')),
  ),
  findsNothing,
);

但是我如何组合这些查找器来验证是否存在带有“计数器”键且文本为“0”的小部件？例如：

Text(
  '$_counter',
  key: const Key('counter'),
  style: Theme.of(context).textTheme.headline4,
),

我有一个 Flutter 小部件，它接受用户输入并使用自定义画家绘制到画布上：

class SPPoint {
  final Point point;
  final double size;
  SPPoint(this.point, this.size);
  String toString() => "SPPoint $point $size";
}

class SignaturePadPainter extends CustomPainter {
  final List<SPPoint> allPoints;
  final SignaturePadOptions opts;
  Canvas _lastCanvas;
  Size _lastSize;

  SignaturePadPainter(this.allPoints, this.opts);

  ui.Image getPng() {
    if (_lastCanvas == null) {
      return null;
    }
    if (_lastSize == null) {
      return null;
    }
    var recorder = new ui.PictureRecorder();
    var origin = new Offset(0.0, 0.0);
    var paintBounds = new Rect.fromPoints(_lastSize.topLeft(origin), _lastSize.bottomRight(origin));
    var canvas = new Canvas(recorder, paintBounds); …