一、解读
// 组件的边框,继承于抽象类 BoxBorder
class Border extends BoxBorder {
// 创建一个边框,参数不能为空
const Border({
this.top = BorderSide.none, // BorderSide.none 是无边框
this.right = BorderSide.none,
this.bottom = BorderSide.none,
this.left = BorderSide.none,
}) : assert(top != null), // 参数不能为空的断言
assert(right != null),
assert(bottom != null),
assert(left != null);
// 创建和一个边相同的边
const Border.fromBorderSide(BorderSide side)
: assert(side != null),
top = side,
right = side,
bottom = side,
left = side;
/// 创建水平 (顶部和底部)和垂直(左边和右边)的边
const Border.symmetric({
BorderSide vertical = BorderSide.none, // 垂直
BorderSide horizontal = BorderSide.none, // 水平
}) : assert(vertical != null),
assert(horizontal != null),
left = vertical,
top = horizontal,
right = vertical,
bottom = horizontal;
/// 所有颜色和宽度都相同的边框
/// 调用 fromBorderSide 来实现
factory Border.all({
Color color = const Color(0xFF000000),
double width = 1.0,
BorderStyle style = BorderStyle.solid,// 边框的样式,实线
}) {
final BorderSide side = BorderSide(color: color, width: width, style: style);
return Border.fromBorderSide(side);
}
/// 创建一个边框,有两个边框相加
static Border merge(Border a, Border b) {
assert(a != null);
assert(b != null);
assert(BorderSide.canMerge(a.top, b.top)); // canMerge 检查是否可以合并,判断的条件是边框的样式和颜色是否相同
assert(BorderSide.canMerge(a.right, b.right));
assert(BorderSide.canMerge(a.bottom, b.bottom));
assert(BorderSide.canMerge(a.left, b.left));
return Border(
top: BorderSide.merge(a.top, b.top),
right: BorderSide.merge(a.right, b.right),
bottom: BorderSide.merge(a.bottom, b.bottom),
left: BorderSide.merge(a.left, b.left),
);
}
// 顶部边框
@override
final BorderSide top;
// 右边边框
final BorderSide right;
// 底部边框
@override
final BorderSide bottom;
// 左边边框
final BorderSide left;
// 获取尺度
@override
EdgeInsetsGeometry get dimensions {
return EdgeInsets.fromLTRB(left.width, top.width, right.width, bottom.width);
}
// 判断边框的颜色、粗细、样式是否一致
@override
bool get isUniform => _colorIsUniform && _widthIsUniform && _styleIsUniform;
// 判断所有边框颜色是否统一
bool get _colorIsUniform {
final Color topColor = top.color;
return right.color == topColor && bottom.color == topColor && left.color == topColor;
}
// 判断边框粗细是否一致
bool get _widthIsUniform {
final double topWidth = top.width;
return right.width == topWidth && bottom.width == topWidth && left.width == topWidth;
}
// 判断边框样式是否一致
bool get _styleIsUniform {
final BorderStyle topStyle = top.style;
return right.style == topStyle && bottom.style == topStyle && left.style == topStyle;
}
// 重写 BoxBorder 的 add 方法,增加边框的数值
@override
Border? add(ShapeBorder other, { bool reversed = false }) {
if (other is Border && // is 是类型判断
BorderSide.canMerge(top, other.top) &&
BorderSide.canMerge(right, other.right) &&
BorderSide.canMerge(bottom, other.bottom) &&
BorderSide.canMerge(left, other.left)) {
return Border.merge(this, other);
}
return null;
}
// 重写 BoxBorder 的父类 ShapeBorder 的 scale 方法,比例增加边框的粗细
@override
Border scale(double t) {
return Border(
top: top.scale(t),
right: right.scale(t),
bottom: bottom.scale(t),
left: left.scale(t),
);
}
//
@override
ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
if (a is Border)
return Border.lerp(a, this, t);
return super.lerpFrom(a, t);
}
@override
ShapeBorder? lerpTo(ShapeBorder? b, double t) {
if (b is Border)
return Border.lerp(this, b, t);
return super.lerpTo(b, t);
}
/// 生成两个边框之间的线性边框
/// 注意: t ==0 ,a 生效;t == 1, b 生效
/// 最后,边框的宽度为 a * (1.0 - t) + b * t
static Border? lerp(Border? a, Border? b, double t) {
assert(t != null);
if (a == null && b == null)
return null;
if (a == null)
return b!.scale(t);
if (b == null)
return a.scale(1.0 - t);
return Border(
top: BorderSide.lerp(a.top, b.top, t),
right: BorderSide.lerp(a.right, b.right, t),
bottom: BorderSide.lerp(a.bottom, b.bottom, t),
left: BorderSide.lerp(a.left, b.left, t),
);
}
/// 在给定大小画布上绘制边框
@override
void paint(
Canvas canvas,
Rect rect, {
TextDirection? textDirection, // 文字方向
BoxShape shape = BoxShape.rectangle, // 形状
BorderRadius? borderRadius, // 圆角
}) {
// 判断是否统一
if (isUniform) {
// 判断边框样式
switch (top.style) {
// 无样式,不绘制
case BorderStyle.none:
return;
// 实线
case BorderStyle.solid:
// 组件的样式
switch (shape) {
// 圆弧型
case BoxShape.circle:
assert(borderRadius == null, 'A borderRadius can only be given for rectangular boxes.');
BoxBorder._paintUniformBorderWithCircle(canvas, rect, top);
break;
// 长方型
case BoxShape
BoxBorder._paintUniformBorderWithRectangle(canvas, rect, top);
break;
}
return;
}
}
assert(() {
// 判断圆角
if (borderRadius != null) {
throw FlutterError.fromParts(<DiagnosticsNode>[
ErrorSummary('A borderRadius can only be given for a uniform Border.'),
ErrorDescription('The following is not uniform:'),
if (!_colorIsUniform) ErrorDescription('BorderSide.color'),
if (!_widthIsUniform) ErrorDescription('BorderSide.width'),
if (!_styleIsUniform) ErrorDescription('BorderSide.style'),
]);
}
return true;
}());
assert(() {
// 判断形状
if (shape != BoxShape.rectangle) {
throw FlutterError.fromParts(<DiagnosticsNode>[
ErrorSummary('A Border can only be drawn as a circle if it is uniform'),
ErrorDescription('The following is not uniform:'),
if (!_colorIsUniform) ErrorDescription('BorderSide.color'),
if (!_widthIsUniform) ErrorDescription('BorderSide.width'),
// 边框的运算
@override
bool operator ==(Object other) {
if (identical(this, other))
return true;
if (other.runtimeType != runtimeType)
return false;
return other is Border
&& other.top == top
&& other.right == right
&& other.bottom == bottom
&& other.left == left;
}
// 获取组件的哈希吗
@override
int get hashCode => hashValues(top, right, bottom, left);
// 获取对该类的描述
@override
String toString() {
if (isUniform)
return '${objectRuntimeType(this, 'Border')}.all($top)';
final List<String> arguments = <String>[
if (top != BorderSide.none) 'top: $top',
if (right != BorderSide.none) 'right: $right',
if (bottom != BorderSide.none) 'bottom: $bottom',
if (left != BorderSide.none) 'left: $left',
];
return '${objectRuntimeType(this, 'Border')}(${arguments.join(", ")})';
}
}
二、总结
- 继承于 Border ,而 Border 继承于 BoxBorder .
- 边框的快捷创建方法以及运算
三、实例
// 颜色、边框样式、粗细
Border.all(
color: Colors.green,
width: 3,
style: BorderStyle.solid,
)
// 从一边生成相同的多边
Border.fromBorderSide(
BorderSide(
color: Colors.green,
width: 3,
style: BorderStyle.solid,
),
)
// 合并两个边框,生成新的边框
// 注意:合并的两个边框的颜色和样式要一样
Border.merge(Border.all(width: 2), Border.all(width: 3))
// 设置水平边框和垂直边框
Border.symmetric(
vertical: BorderSide(
color: Colors.green,
width: 5,
),
horizontal: BorderSide(
color: Colors.black,
width: 5,
),
)
// 判断两个边框是否相等
Border(top: BorderSide(color: Colors.green)) == Border(top: BorderSide(color: Colors.red))
// 生成两个边框的线性插值边框
Border.lerp(
Border(top: BorderSide(color: Colors.green, width: 10)),
Border(top: BorderSide(color: Colors.purple, width: 2)),
2,
)