Flutter MVVM 实用框架

发表于 3年以前 | 总阅读数：2385 次

基于Provider实现MVVM框架，常用的方式是 ViewModel 继承 ChangeNotifier ，再通过 ChangeNotifierProvider 提供给子Widget，ViewModel数据刷新通过调用 notifyListeners() 来通知Widget进行刷新，Widget 通过 Provider.of 、Consumer、Selector 来监听数据变化重新 build 更新UI。这种方式存在的问题有：

ViewModel数据刷新需要每次调用 notifyListeners()容易被遗漏
notifyListeners()作用在整个ViewModel，不方便进行局部UI刷新控制
Selector 虽然可以控制局部刷新，但需要需要自定义 shouldRebuild 要去了解Provider原理
缺少 ViewModel 和 Widget 生命周期的管理

ViewModelProvider 在兼容现有功能基础刷，实现最小改动、不需要每次调用notifyListeners()、支持局部刷新UI和生命周期管理的框架

先给出源码后续有空再详细介绍 https://github.com/wittyneko/view_model_provider

局部刷新控制

通过ValueNotifier创建可观察对象 ``java class ViewModel extends ChangeNotifier { final value1 = ValueNotifier(0); final value2 = ValueNotifier(0); }

2. 通过 ValueListenableBuilder 监听数据变化刷新
```java
ValueListenableBuilder(
  valueListenable: viewModel.value1,
  builder: (context, value, child) {
    debugPrint("ValueListenableBuilder $value");
    return Text("ValueListenableBuilder $value");
    },
)

列表刷新控制

1 . 通过 ListNotifier 创建可观察对象

class ViewModel extends ChangeNotifier {
  final list = ListNotifier<String>([]);
}

2 . 通过 ListListenableBuilder 监听数据变化刷新

ListListenableBuilder(
  valueListenable: viewModel.list,
  builder: (context, value, child) {
    debugPrint("ValueListenableBuilder $value");
    return Text("ValueListenableBuilder $value");
    },
)

实现生命周期管理

LifecycleWidget，提供Widget生命周期监听，开放了以下回调接口可进行初始化和解绑操作

create，可以监听一个数据变化
initState，Widget initState 回调
initFrame，Widget 第一帧绘制完成调用
deactivate，Widget deactivate 回调
dispose，Widget dispose 回调
didUpdateWidget，Widget didUpdateWidget 回调
didChangeDependencies，Widget didChangeDependencies 回调

ViewModelProvider

创建ViewModel 提供给子Widget使用，开放了以下回调接口可进行初始化和解绑操作

initViewModel，ViewModel首次初始化 Widget initState 期间执行
bindViewModel，ViewModel 首次绑定 Widget ，方法在Widget build 期间执行
disposeViewModel，ViewModel 销毁，Widget dispose 时执行

/// [ViewModelProvider] 创建ViewModel
class ProviderExample extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ViewModelProvider<ViewModel>(
      create: (_) => ViewModel(),
      initViewModel: (context, viewModel) {
        debugPrint("ProviderBuilderExample initViewModel $viewModel");
      },
      bindViewModel: (context, viewModel) {
        debugPrint("ProviderBuilderExample bindViewModel $viewModel");
      },
      disposeViewModel: (context, viewModel) {
        debugPrint("ProviderBuilderExample disposeViewModel $viewModel");
      },
      builder: (context, viewModel, child) {
        debugPrint("ProviderBuilderExample builder $viewModel");
        return ViewModelWidget(viewModel);
      },
    );
  }
}

另外还可以通过继承ViewModelProviderWidget来创建ViewModel

/// 继承 [ViewModelProviderWidget] 创建ViewModel
class ProviderWidgetExample extends ViewModelProviderWidget<ViewModel> {
  ProviderWidgetExample() : super();

  @override
  ViewModel create(BuildContext context) => ViewModel();

  @override
  void initViewModel(BuildContext context, ViewModel viewModel) {
    debugPrint("ProviderWidgetExample initViewModel $viewModel");
  }

  @override
  void bindViewModel(BuildContext context, ViewModel viewModel) {
    debugPrint("ProviderWidgetExample bindViewModel $viewModel");
  }

  @override
  Widget buildChild(BuildContext context, ViewModel viewModel, Widget child) {
    debugPrint("ProviderWidgetExample build $viewModel");
    return ViewModelWidget(viewModel);
  }
}

ViewModel嵌套处理

ViewModel 嵌套 ViewModel 管理子 ViewModel ，提供了两种方式，一种需要手动调用刷新，另一种通过ValueNotifier包装替换ViewModel不需要手动刷新，同ViewModelProvider一样也有相关的抽象类提供继承支持。

class ParentViewModel extends ChangeNotifier {
  final valueViewModel = ValueNotifier(ChildViewModel());
  var childViewModel = ChildViewModel();

  void valueNotifier() {
    valueViewModel.value = ChildViewModel();
  }

  void notifyListenerChild() {
    childViewModel = ChildViewModel();
    notifyListeners();
  }
}

class ChildViewModel extends ChangeNotifier {
  final value = ValueNotifier(0);

  addValue() {
    value.value++;
  }
}

1 通过 ViewModelProvider 创建父ViewModel

class ChildProviderExapmle extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ViewModelProvider<ParentViewModel>(
      create: (context) => ParentViewModel(),
      builder: (context, viewModel, child) {
        return Scaffold(
          body: Container(
            child: Column(
              children: [
                ValueViewModelProviderExample(),
                ChildViewModelProviderExample(),
                ElevatedButton(
                  onPressed: () => viewModel.valueNotifier(),
                  child: Text("valueNotifier"),
                ),
                ElevatedButton(
                  onPressed: () => viewModel.notifyListenerChild(),
                  child: Text("notifyListenerChild"),
                ),
              ],
            ),
          ),
        );
      },
    );
  }
}

2 创建子ViewModelProvider

2-1 ChildViewModelProvider

需要手动刷新通常用于列表刷新Item区域，在ViewModelProvider已有回调基础上添加了

changeViewModel ，在子 ViewModel 被替换后可重新执行绑定流程

/// [ChildViewModelProvider] 获取子 ViewModel 例子
class ChildViewModelProviderExample extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ChildViewModelProvider<ParentViewModel, ChildViewModel>(
      create: (_, parent) => parent.childViewModel,
      changeViewModel: (context, parent, viewModel, oldViewModel) {
        debugPrint(
            "ChildViewModelProvider changeViewModel $viewModel, $oldViewModel");
      },
      builder: (context, parent, viewModel, child) {
        debugPrint("ChildViewModelProvider builder $viewModel");
        return Row(
          children: [
            ValueListenableBuilder(
              valueListenable: viewModel.value,
              builder: (context, value, child) => Text("${viewModel.value}"),
            ),
            ElevatedButton(
              onPressed: () => viewModel.addValue(),
              child: Text("addValue"),
            )
          ],
        );
      },
    );
  }
}

2-2 ValueViewModelProvider

作用和回调与 ChildViewModelProvider一样，接收数据类型为 ValueListenable<ChangeNotifier>

/// [ValueViewModelProvider] 获取子 ViewModel 例子
class ValueViewModelProviderExample extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ValueViewModelProvider<ParentViewModel, ChildViewModel>(
      create: (_, parent) => parent.valueViewModel,
      changeViewModel: (context, parent, viewModel, oldViewModel) {
        debugPrint(
            "ValueViewModelProvider changeViewModel $viewModel, $oldViewModel");
      },
      builder: (context, parent, viewModel, child) {
        debugPrint("ValueViewModelProvider builder $viewModel");
        return Row(
          children: [
            ValueListenableBuilder(
              valueListenable: viewModel.value,
              builder: (context, value, child) => Text("${viewModel.value}"),
            ),
            ElevatedButton(
              onPressed: () => viewModel.addValue(),
              child: Text("addValue"),
            )
          ],
        );
      },
    );
  }

获取ViewModel

1 扩展函数

通过context.viewModel<ViewModel>()可以快速取出ViewModelProvider``ChildViewModelProvider和 ValueViewModelProvider的ViewModel，这个方法在Widget build期间使用，如果要在initStatus期间使用可以直接使用Provider提供的扩展context.read<ViewModel>()。

2 ViewModelBuilder

用于取出ViewModelProvider提供的ViewModel

ValueListenableBuilder

ValueListenableBuilder 只能监听当额数据刷新，同时监听多个数据刷新可采用ValueTuple2WidgetBuilder到ValueListenableTuple7Builder 和 ValueListenableListBuilder

 /// 外部传入 ViewModel，可采用[ValueListenableBuilder]系列监听数据变化
  Widget _buildValueListenable(ViewModel viewModel) {
    return Column(
      children: [
        /// 监听单个数据变化
        ValueListenableBuilder(
            valueListenable: viewModel.value1,
            builder: (context, value, child) {
              debugPrint("ValueListenableBuilder $value");
              return Text("ValueListenableBuilder $value");
            }),
        /// 监听多个数据变化，继承自
        ValueListenableListBuilder(
          valueListenables: [
            viewModel.value1,
            viewModel.value2,
          ],
          builder: (context, value, child) {
            debugPrint(
                "ValueListenableListBuilder ${value.first}, ${value.last}");
            return Text(
                "ValueListenableListBuilder ${value.first}, ${value.last}");
          },
        ),
        /// 监听多个数据变化，继承自[ValueListenableListBuilder]可指定泛型
        ValueListenableTuple2Builder(
          valueListenables: Tuple2(viewModel.value1, viewModel.value2),
          builder: (context, value, child) {
            debugPrint(
                "ValueListenableTuple2Builder ${value.item1}, ${value.item2}");
            return Text(
                "ValueListenableTuple2Builder ${value.item1}, ${value.item2}");
          },
        ),
      ],
    );
  }

ViewModelValueBuilder

ViewModelBuilder 和 ValueListenableBuilder 组合，用于获取 ViewModel 和管理Widget刷新区域。

提供过个实现 ViewModelValueListBuilder，ViewModelValueTuple2Builder 到 ViewModelValueTuple7WidgetBuilder可同时监听多个ViewMode参数变化来刷新Widget

  /// 不通过外部传入 ViewModel，可采用[ViewModelValueBuilder]系列获取 ViewModel 并监听数据变化
  Widget _buildViewModelValue() {
    return Column(
      children: [
        ViewModelValueBuilder(
          valueListenable: (ViewModel viewModel) => viewModel.value1,
          builder: (context, viewModel, value, child) {
            debugPrint("ViewModelValueBuilder $value");
            return Text("ViewModelValueBuilder $value");
          },
        ),
        ViewModelValueListBuilder(
          valueListenables: (ViewModel viewModel) => [
            viewModel.value1,
            viewModel.value2,
          ],
          builder: (context, viewModel, value, child) {
            debugPrint(
                "ViewModelValueListBuilder ${value.first}, ${value.last}");
            return Text(
                "ViewModelValueListBuilder ${value.first}, ${value.last}");
          },
        ),
        ViewModelValueTuple2Builder(
          valueListenables: (ViewModel viewModel) =>
              Tuple2(viewModel.value1, viewModel.value2),
          builder: (context, viewModel, value, child) {
            debugPrint(
                "ViewModelValueTuple2Builder ${value.item1}, ${value.item2}");
            return Text(
                "ViewModelValueTuple2Builder ${value.item1}, ${value.item2}");
          },
        ),
      ],
    );
  }