MaterialTapTargetSize

MaterialTapTargetSize并不是一个组件，是配置组件点击区域大小的属性，很多组件都有materialTapTargetSize属性，比如：

[FloatingActionButton], only the mini tap target size is increased.
* [MaterialButton]
* [OutlineButton]
* [FlatButton]
* [RaisedButton]
* [TimePicker]
* [SnackBar]
* [Chip]
* [RawChip]
* [InputChip]
* [ChoiceChip]
* [FilterChip]
* [ActionChip]
* [Radio]
* [Switch]
* [Checkbox]

MaterialTapTargetSize有2个值，分别为：

• padded：最小点击区域为48*48。
• shrinkWrap：子组件的实际大小。

源码如下：

BoxConstraints constraints;
switch (widget.materialTapTargetSize ?? theme.materialTapTargetSize) {
  case MaterialTapTargetSize.padded:
    constraints = const BoxConstraints(minHeight: kMinInteractiveDimension);
    break;
  case MaterialTapTargetSize.shrinkWrap:
    constraints = const BoxConstraints();
    break;
}

kMinInteractiveDimension值为48。