Flutter Sliver滚动组件的演示代码

flutter sliver滚动组件

 sliverlist & slivergrid

需要同时滚动listview和gridview时可以使用sliverlist和slivergrid。

customscrollview(
    slivers: [
        sliverlist(
            delegate: sliverchildbuilderdelegate(
                (context, index) {
                    return container(
                        height: 50,
                        color: colors.primaries[index % colors.primaries.length],
                    );
                },
                childcount: 5,
            ),
        ),
        slivergrid(
            griddelegate: slivergriddelegatewithfixedcrossaxiscount(
                crossaxiscount: 3,
                crossaxisspacing: 5,
                mainaxisspacing: 5,
            ),
            delegate: sliverchildbuilderdelegate(
                (buildcontext context, int index) {
                    return container(
                        color: colors.primaries[index % colors.primaries.length],
                    );
                },
                childcount: 20,
            ),
        ),
    ],
)

sliverappbar

pinned：是否固定在屏幕顶部。

expandedheight：展开区域的高度。

flexiblespace：展开取消显示内容。

customscrollview(
    slivers: [
        sliverappbar(
            pinned: true,
            expandedheight: 200,
            flexiblespace: flexiblespacebar(
                title: const text("sliverappbar"),
                background: image.asset("images/avatar.jpg", fit: boxfit.cover),
            ),
        ),
        sliverfixedextentlist(
            delegate: sliverchildbuilderdelegate(
                (buildcontext context, int index) {
                    return container(
                        alignment: alignment.center,
                        color: colors.primaries[index % colors.primaries.length],
                        child: text("$index"),
                    );
                },
            ),
            itemextent: 50.0,
        ),
    ],
)

sliverpersistentheader

sliverpersistentheader组件可以控制滚动的最大高度和最小高度，类似sliverappbar效果。

build：显示内容。

maxextent & minextent：滚动的高度范围。

shouldrebuild：是否需要更新。

customscrollview(
    slivers: [
        sliverpersistentheader(
            pinned: true,
            delegate: mysliverpersistentheaderdelegate(),
        ),
        slivergrid(
            griddelegate: slivergriddelegatewithfixedcrossaxiscount(
                crossaxiscount: 3,
                crossaxisspacing: 5,
                mainaxisspacing: 5,
            ),
            delegate: sliverchildbuilderdelegate(
                (buildcontext context, int index) {
                    return container(
                        color: colors.primaries[index % colors.primaries.length],
                    );
                },
            ),
        ),
    ],
)

class mysliverpersistentheaderdelegate extends sliverpersistentheaderdelegate {
    @override
    widget build(
        buildcontext context, double shrinkoffset, bool overlapscontent) {
        return container(
            color: colors.blue,
            alignment: alignment.center,
            child: text(
                "hello world",
                style: textstyle(color: colors.white),
            ),
        );
    }

    @override
    double get maxextent => 200;

    @override
    double get minextent => 50;

    @override
    bool shouldrebuild(covariant sliverpersistentheaderdelegate olddelegate) {
        return false;
    }
}

slivertoboxadapter

customscrollview只能包含sliver组件，如果需要使用普通组件可以使用slivertoboxadapter。

customscrollview(
    slivers: [
        slivertoboxadapter(
            child: container(
                height: 200,
                color: colors.black26,
                alignment: alignment.center,
                child: text("hello world"),
            ),
        ),
        sliverlist(
            delegate: sliverchildbuilderdelegate(
                (buildcontext context, int index) {
                    return container(
                        height: 60,
                        color: colors.primaries[index % colors.primaries.length],
                    );
                },
                childcount: 50,
            ),
        ),
    ],
)

customscrollview & nestedscrollview

customscrollview组件可以将多个组件组合在一起，具有统一的滚动效果，但是customscrollview只能嵌套sliver系列的组件，如sliverlist、slivergrid、sliverpadding、sliverappbar等。

nestedscrollview可以协调两个滚动组件滑动。nestedscrollview在逻辑上将可滚动组件分为header和body两部分，heade部分只能接收sliver类型的组件，而body部分可以接收任意类型的组件。

nestedscrollview+sliverappbar+sliverfixedextentlist+listview

nestedscrollview(
    //sliver组件
    headersliverbuilder: (buildcontext context, bool innerboxisscrolled) {
        return [
            sliverappbar(
                title: const text("嵌套listview"),
                pinned: true, //固定appbar             
                forceelevated: true,
            ),
            sliverfixedextentlist(
                itemextent: 50,
                delegate: sliverchildbuilderdelegate(
                    (buildcontext context, int index) {
                        return listtile(title: text("$index"));
                    },
                    childcount: 5,
                ),
            ),
        ];
    },
    //滚动组件
    body: listview.builder(
        padding: const edgeinsets.all(8),
        physics: const clampingscrollphysics(), //需要
        itemcount: 30,
        itembuilder: (buildcontext context, int index) {
            return sizedbox(
                height: 50,
                child: center(child: text("item $index")),
            );
        },
    ),
)

nestedscrollview+sliverappbar+customscrollview

nestedscrollview(
    headersliverbuilder: (buildcontext context, bool innerboxisscrolled) {
        return [
            sliverappbar(
                floating: true,
                snap: true,
                expandedheight: 200,
                forceelevated: innerboxisscrolled,
                flexiblespace: flexiblespacebar(
                    background: image.asset(
                        "images/logo.png",
                        fit: boxfit.cover,
                    ),
                ),
            ),
        ];
    },
    body: customscrollview(
        slivers: [buildsliverlist(50)],
    ),
)

优化联动效果

sliverappbar+customscrollview组合，当反向滑动时，sliverappbar就会整体回到屏幕顶部，出现遮挡问题，为了解决该问题，可以用在header里用sliveroverlapabsorber组件包裹sliverappbar，body里sliver列表最前面添加一个sliveroverlapinjector。

nestedscrollview(
    headersliverbuilder: (buildcontext context, bool innerboxisscrolled) {
        return [
            sliveroverlapabsorber(
                handle: nestedscrollview.sliveroverlapabsorberhandlefor(context),
                sliver: sliverappbar(
                    floating: true,
                    snap: true,
                    expandedheight: 200,
                    forceelevated: innerboxisscrolled,
                    flexiblespace: flexiblespacebar(
                        background: image.asset(
                            "images/logo.png",
                            fit: boxfit.cover,
                        ),
                    ),
                ),
            ),
        ];
    },
    body: builder(
        builder: (buildcontext context) {
            return customscrollview(
                slivers: [
                    sliveroverlapinjector(
                        handle: nestedscrollview.sliveroverlapabsorberhandlefor(context),
                    ),
                    buildsliverlist(50),
                ],
            );
        },
    ),
)

nestedscrollview+tabbarview

class mypageview extends statefulwidget {
    late list<string> tabs;

    mypageview({key? key, required this.tabs}) : super(key: key);

    @override
    state<statefulwidget> createstate() {
        return _mypageviewstate();
    }
}

class _mypageviewstate extends state<mypageview>
    with singletickerproviderstatemixin {
    late tabcontroller _controller;

    @override
    void initstate() {
        super.initstate();
        _controller = tabcontroller(length: widget.tabs.length, vsync: this);
    }

    @override
    void dispose() {
        super.dispose();
        _controller.dispose();
    }

    @override
    widget build(buildcontext context) {
        return nestedscrollview(
            headersliverbuilder: (buildcontext context, bool innerboxisscrolled) {
                return [
                    sliveroverlapabsorber(
                        handle: nestedscrollview.sliveroverlapabsorberhandlefor(context),
                        sliver: sliverappbar(
                            title: const text("hi flutter"),
                            floating: true,
                            snap: true,
                            forceelevated: innerboxisscrolled,
                            bottom: tabbar(
                                controller: _controller,
                                tabs: widget.tabs.map((e) => tab(text: e)).tolist(),
                            ),
                        ),
                    ),
                ];
            },
            body: tabbarview(
                controller: _controller,
                children: widget.tabs.map((e) {
                    return builder(builder: (buildcontext context) {
                        return customscrollview(
                            key: pagestoragekey(e),
                            slivers: [
                                sliveroverlapinjector(
                                    handle:
                                    nestedscrollview.sliveroverlapabsorberhandlefor(context),
                                ),
                                sliverpadding(
                                    padding: const edgeinsets.all(9),
                                    sliver: buildsliverlist(50),
                                ),
                            ],
                        );
                    });
                }).tolist(),
            ),
        );
    }
}

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