在flutter中只用GestureDetector添加点击事件，发现在空白区域点击无效，事件不响应。解决办法：

GestureDetector(
behavior: HitTestBehavior.opaque,
)

说明:

/// How to behave during hit tests.
enum HitTestBehavior {
  /// Targets that defer to their children receive events within their bounds
  /// only if one of their children is hit by the hit test.
  deferToChild,

  /// Opaque targets can be hit by hit tests, causing them to both receive
  /// events within their bounds and prevent targets visually behind them from
  /// also receiving events.
  opaque,

  /// Translucent targets both receive events within their bounds and permit
  /// targets visually behind them to also receive events.
  translucent,
}