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Flutter系列重學(xué)Container示例詳解

 更新時(shí)間：2023年01月19日 10:49:28   作者：SoaringHeart  
這篇文章主要為大家介紹了Flutter系列重學(xué)Container示例詳解，有需要的朋友可以借鑒參考下，希望能夠有所幫助，祝大家多多進(jìn)步，早日升職加薪

一、Container 簡(jiǎn)介

flutter 開(kāi)發(fā)中最核心的是用最少的組件（層次）完成功能開(kāi)發(fā)；Container 前端的盒子模型實(shí)現(xiàn)，類似 div 標(biāo)簽，掌握其他組件前，深入學(xué)習(xí)理解 Container 的使用是必要的。

Container是一個(gè)組合類容器，由DecoratedBox、ConstrainedBox、Transform、Padding、Align等組件組合的一個(gè)多功能容器，所以我們只需通過(guò)一個(gè)Container組件可以實(shí)現(xiàn)同時(shí)需要裝飾、變換、約束限制的場(chǎng)景。

二、示例

  • 示例包含透明度，背景裝飾，前景裝飾，child 模糊度，紅色部分是 child；

buildSection() {
  return Opacity(
    opacity: 1,
    child: Container(
      margin: EdgeInsets.all(20),
      padding: EdgeInsets.all(20),
      decoration: BoxDecoration(
        borderRadius: BorderRadius.all(Radius.circular(20)),
        gradient: LinearGradient(
          colors: [Colors.green, Colors.yellow],
          begin: Alignment.topCenter,
          end: Alignment.bottomCenter,
        ),
        boxShadow: [
          BoxShadow(
            color: Colors.red.withOpacity(0.5),
            spreadRadius: 5,
            blurRadius: 7,
            offset: Offset(0, 3), // changes position of shadow
          ),
        ],
        image: DecorationImage(
          image: NetworkImage('https://tenfei02.cfp.cn/creative/vcg/800/new/VCG21409037867.jpg'),
          fit: BoxFit.cover,
        ),
      ),
      foregroundDecoration: BoxDecoration(
        color: Colors.yellow,
        border: Border.all(color: Colors.green, width: 5),
        borderRadius: BorderRadius.all(Radius.circular(400)),
        image: DecorationImage(
          image: NetworkImage('https://pic.616pic.com/bg_w1180/00/04/08/G5Bftx5ZDI.jpg'),
          fit: BoxFit.cover,
        ),
      ),
      child: BackdropFilter(
        filter: ui.ImageFilter.blur(sigmaX: 10.0, sigmaY: 10.0),
        child: Container(
          constraints: BoxConstraints.expand(),
          decoration: BoxDecoration(
            borderRadius: BorderRadius.all(Radius.circular(20)),
            color: Colors.red,
          ),
          child: Text('VCG21409037867'),
        ),
      ),
    ),
  );
}
  • 實(shí)現(xiàn)背景圖 background-repeat 顯示，flutter支持四種類型：
enum ImageRepeat {
  repeat,
  repeatX,
  repeatY,
  noRepeat,
}

這里以第一種 ImageRepeat.repeat 為例：

Container(
  decoration: BoxDecoration(
    image: DecorationImage(
      image: AssetImage('images/img_update.png'),
      repeat: ImageRepeat.repeat,
      alignment: Alignment.topLeft,
    )
  ),
  child: Container(
    constraints: BoxConstraints.expand(),
    child: OutlinedButton(
      onPressed: () { print("ImageRepeat.repeat"); },
      child: Text('ImageRepeat.repeat',
        style: TextStyle(fontWeight: FontWeight.bold, color: Colors.red),
      ),
    ),
  ),
),

transform && alignment

Container(
  decoration: BoxDecoration(
    image: DecorationImage(
      image: AssetImage('images/img_update.png'),
      repeat: ImageRepeat.repeat,
      alignment: Alignment.topLeft,
    )
  ),
  transform: Matrix4.rotationZ(.2),//變化
  alignment: Alignment.centerRight, //卡片文字對(duì)齊
  child: Text(
    "5.20", style: TextStyle(color: Colors.red, fontSize: 40.0),
  ),
),

三、源碼分析

class Container extends StatelessWidget {
  Container({
    Key? key,
    this.alignment,
    this.padding,
    this.color,
    this.decoration,
    this.foregroundDecoration,
    double? width,
    double? height,
    BoxConstraints? constraints,
    this.margin,
    this.transform,
    this.transformAlignment,
    this.child,
    this.clipBehavior = Clip.none,
  })：super(key: key);
  // 子項(xiàng)
  final Widget? child;
  // 內(nèi)邊距
  final EdgeInsetsGeometry? padding;
  // 背景色，和 decoration 只能二選一
  final Color? color;
  // 背景裝飾
  final Decoration? decoration;
  // 前景裝飾（在 child 之上）
  final Decoration? foregroundDecoration;
  // 約束條件
  final BoxConstraints? constraints;
  // 外邊距
  final EdgeInsetsGeometry? margin;
  // 變化
  final Matrix4? transform;
  // 變化之后  child 對(duì)齊方式
  final AlignmentGeometry? transformAlignment;
  // 裁剪方式
  final Clip clipBehavior;
  EdgeInsetsGeometry? get _paddingIncludingDecoration {
    if (decoration == null || decoration!.padding == null)
      return padding;
    final EdgeInsetsGeometry? decorationPadding = decoration!.padding;
    if (padding == null)
      return decorationPadding;
    return padding!.add(decorationPadding!);
  }
  @override
  Widget build(BuildContext context) {
    Widget? current = child;
    if (child == null && (constraints == null || !constraints!.isTight)) {
      current = LimitedBox(
        maxWidth: 0.0,
        maxHeight: 0.0,
        child: ConstrainedBox(constraints: const BoxConstraints.expand()),
      );
    }
    if (alignment != null)
      current = Align(alignment: alignment!, child: current);
    final EdgeInsetsGeometry? effectivePadding = _paddingIncludingDecoration;
    if (effectivePadding != null)
      current = Padding(padding: effectivePadding, child: current);
    if (color != null)
      current = ColoredBox(color: color!, child: current);
    if (clipBehavior != Clip.none) {
      assert(decoration != null);
      current = ClipPath(
        clipper: _DecorationClipper(
          textDirection: Directionality.maybeOf(context),
          decoration: decoration!,
        ),
        clipBehavior: clipBehavior,
        child: current,
      );
    }
    if (decoration != null)
      current = DecoratedBox(decoration: decoration!, child: current);
    if (foregroundDecoration != null) {
      current = DecoratedBox(
        decoration: foregroundDecoration!,
        position: DecorationPosition.foreground,
        child: current,
      );
    }
    if (constraints != null)
      current = ConstrainedBox(constraints: constraints!, child: current);
    if (margin != null)
      current = Padding(padding: margin!, child: current);
    if (transform != null)
      current = Transform(transform: transform!, alignment: transformAlignment, child: current);
    return current!;
  }
  ...
}

源碼很簡(jiǎn)單，組件層層包裹，但是我們必須清楚每一個(gè)參數(shù)的作用和使用場(chǎng)景。它可以幫你用更少的層級(jí)完成功能，這很重要。

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