Android MVVM架构组件：如何从列表片段更新单个数据实体？

Question

我一直在努力学习新的Android架构组件。 我一直在将我的应用程序基于此示例： 基本示例

我有它工作，但我坚持如何插入，更新或删除Room数据库中的数据。 在示例中，它没有提供这些示例。

关于示例，我试图弄清楚如何从ProductListFragment对每个产品进行更改。 在我的应用程序中，我不是使用Product而是使用已定义的Zone。 因此，例如在列表中我想要一个按钮，按下时将删除该区域。 或者可以更新区域属性的按钮，例如区域具有活动属性。 当按钮单击该CardView时，它将更新区域的活动属性。

ZoneListFragment

public class ZoneListFragment extends android.support.v4.app.Fragment {

    public static final String TAG = "ZoneListViewModel";
    private ZoneAdapter mZoneAdapter;
    private FragmentZoneListBinding mBinding;
    private ZoneListViewModel viewModel;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container,
                             @Nullable Bundle savedInstanceState) {
        mBinding = DataBindingUtil.inflate(inflater, R.layout.fragment_zone_list, container, false);

        mZoneAdapter = new ZoneAdapter(mZoneClickCallback, mZoneDirectionClickCallback);
        mBinding.zonesList.setAdapter(mZoneAdapter);

        return mBinding.getRoot();
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        viewModel = ViewModelProviders.of(this).get(ZoneListViewModel.class);
        subscribeUi(viewModel);
    }

    private void subscribeUi(ZoneListViewModel viewModel) {
        // Update the list when the data changes
        viewModel.getZones().observe(this, new Observer<List<ZoneEntity>>() {
            @Override
            public void onChanged(@Nullable List<ZoneEntity> myZones) {
                if (myZones != null) {
                    mBinding.setIsLoading(false);
                    mZoneAdapter.setZoneList(myZones);
                } else {
                    mBinding.setIsLoading(true);
                }
                mBinding.executePendingBindings();
            }
        });
    }

    private final ZoneClickCallback mZoneClickCallback = new ZoneClickCallback() {
        @Override
        public void onClick(Zone zone) {

        }
    };

    private final ZoneDirectionClickCallback mZoneDirectionClickCallback = new ZoneDirectionClickCallback() {
        @Override
        public void onClick(Zone zone) {
            zone.setDirection(zone.isDirection() ? false : true);
            viewModel.updateZone(zone);
        }
    };
}

ZoneListViewModel

public class ZoneListViewModel extends AndroidViewModel {
    private final MediatorLiveData<List<ZoneEntity>> mObservableZones;
    private DataRepository repository;

    public ZoneListViewModel(Application application) {
        super(application);

        mObservableZones = new MediatorLiveData<>();
        // set by default null, until we get data from the database.
        mObservableZones.setValue(null);

        LiveData<List<ZoneEntity>> zones = ((Zoneify) application).getRepository()
                .getZones();

        // observe the changes of the zones from the database and forward them
        mObservableZones.addSource(zones, mObservableZones::setValue);
    }

    public LiveData<List<ZoneEntity>> getZones() {
        return mObservableZones;
    }
}

ZoneAdapter

public class ZoneAdapter extends RecyclerView.Adapter<ZoneAdapter.ZoneViewHolder> {

    List<? extends Zone> mZoneList;

    @Nullable
    private final ZoneClickCallback mZoneClickCallback;
    @Nullable
    private final ZoneDirectionClickCallback mZoneDirectionClickCallback;

    public ZoneAdapter(@Nullable ZoneClickCallback zoneClickCallback,
                       @Nullable ZoneDirectionClickCallback zoneDirectionClickCallback) {
        mZoneClickCallback = zoneClickCallback;
        mZoneDirectionClickCallback = zoneDirectionClickCallback;
    }

    public void setZoneList(final List<? extends Zone> zoneList) {
        if (mZoneList == null) {
            mZoneList = zoneList;
            notifyItemRangeInserted(0, zoneList.size());
        } else {
            DiffUtil.DiffResult result = DiffUtil.calculateDiff(new DiffUtil.Callback() {
                @Override
                public int getOldListSize() {
                    return mZoneList.size();
                }

                @Override
                public int getNewListSize() {
                    return zoneList.size();
                }

                @Override
                public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
                    return mZoneList.get(oldItemPosition).getId() ==
                            zoneList.get(newItemPosition).getId();
                }

                @Override
                public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
                    Zone newZone = zoneList.get(newItemPosition);
                    Zone oldZone = mZoneList.get(oldItemPosition);
                    return newZone.getId() == oldZone.getId()
                            && Objects.equals(newZone.getName(), oldZone.getName())
                            && Objects.equals(newZone.getAddress(), oldZone.getAddress())
                            && newZone.isActive() == oldZone.isActive()
                            && newZone.isDirection() == oldZone.isDirection()
                            && Objects.equals(newZone.getLatLng(), oldZone.getLatLng())
                            && Objects.equals(newZone.getNotification(), oldZone.getNotification());
                }
            });
            mZoneList = zoneList;
            result.dispatchUpdatesTo(this);
        }
    }

    @Override
    public ZoneViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        ZoneItemBinding binding = DataBindingUtil
                .inflate(LayoutInflater.from(parent.getContext()), R.layout.zone_item,
                        parent, false);
        binding.setZoneClickcallback(mZoneClickCallback);
        binding.setZoneDirectionClickCallback(mZoneDirectionClickCallback);
        return new ZoneViewHolder(binding);
    }

    @Override
    public void onBindViewHolder(ZoneViewHolder holder, int position) {
        holder.binding.setZone(mZoneList.get(position));
        holder.binding.executePendingBindings();
    }

    @Override
    public int getItemCount() {
        return mZoneList == null ? 0 : mZoneList.size();
    }

    static class ZoneViewHolder extends RecyclerView.ViewHolder {

        final ZoneItemBinding binding;

        public ZoneViewHolder(ZoneItemBinding binding) {
            super(binding.getRoot());
            this.binding = binding;
        }
    }
}

zone_item.xml

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:map="http://schemas.android.com/tools">
    <data>
        <variable name="zone"
            type="com.davidh.zoneify.data.model.Zone"/>
        <variable name="zoneClickcallback"
            type="com.davidh.zoneify.view.ZoneClickCallback"/>
        <variable name="zoneDirectionClickCallback"
            type="com.davidh.zoneify.view.ZoneDirectionClickCallback"/>
    </data>

    <android.support.v7.widget.CardView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:minHeight="100dp"
        android:onClick="@{() ->  callback.onClick(zone)}"
        android:orientation="horizontal"
        android:layout_marginStart="8dp"
        android:layout_marginEnd="8dp"
        app:cardUseCompatPadding="true">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="125dp"
            android:orientation="horizontal"
            android:background="@color/colorPrimary">

            <com.google.android.gms.maps.MapView
                android:id="@+id/map"
                android:layout_width="0dp"
                android:layout_weight="1"
                android:layout_height="match_parent"
                map:cameraZoom="15"
                map:mapType="normal"
                map:liteMode="true"
                app:initMap="@{zone.latLng}"/>

            <LinearLayout
                android:layout_width="0dp"
                android:layout_weight="3"
                android:layout_height="match_parent"
                android:orientation="vertical">

                <LinearLayout
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:orientation="vertical">

                    <TextView
                        android:layout_width="match_parent"
                        android:layout_height="wrap_content"
                        android:layout_marginLeft="10dp"
                        android:layout_marginTop="5dp"
                        android:text="@{zone.name}"
                        android:textAppearance="@style/TextAppearance.AppCompat.Title.Inverse"/>

                    <TextView
                        android:layout_width="match_parent"
                        android:layout_height="wrap_content"
                        android:layout_marginLeft="10dp"
                        android:layout_marginTop="5dp"
                        android:text="@{zone.notification}"
                        android:textAppearance="@style/TextAppearance.AppCompat.Small.Inverse"/>

                </LinearLayout>

                <LinearLayout
                    android:layout_width="match_parent"
                    android:layout_height="fill_parent"
                    android:orientation="horizontal"
                    android:layout_gravity="center|bottom">

                    <Button
                        android:layout_width="0dp"
                        android:layout_height="@dimen/imageButtonCardView"
                        android:layout_weight="1"
                        android:layout_gravity="center_horizontal|center|center_vertical"
                        android:background="@color/colorPrimary"
                        android:textAppearance="@style/TextAppearance.AppCompat.Widget.Button.Inverse"
                        style="?android:attr/borderlessButtonStyle"
                        android:id="@+id/btn_zone_direction"
                        android:drawableTop="@{zone.direction ? @drawable/ic_leaving_24 : @drawable/ic_entering_24}"
                        android:text="@{zone.direction ? @string/leaving : @string/entering}"
                        android:onClick="@{() ->  directionCallback.onClick(zone)}"/>

                    <Button
                        android:layout_width="0dp"
                        android:layout_height="@dimen/imageButtonCardView"
                        android:layout_weight="1"
                        android:layout_gravity="center_horizontal|center|center_vertical"
                        android:background="@color/colorPrimary"
                        android:textAppearance="@style/TextAppearance.AppCompat.Widget.Button.Inverse"
                        style="?android:attr/borderlessButtonStyle"
                        android:id="@+id/btn_zone_active"
                        android:drawableTop="@{zone.active ? @drawable/ic_alarm_on_24 : @drawable/ic_alarm_off_24}"
                        android:text="@{zone.active ? @string/on : @string/off}"/>

                    <Button
                        android:layout_width="0dp"
                        android:layout_height="@dimen/imageButtonCardView"
                        android:layout_weight="1"
                        android:layout_gravity="center_horizontal|center|center_vertical"
                        android:background="@color/colorPrimary"
                        android:textAppearance="@style/TextAppearance.AppCompat.Widget.Button.Inverse"
                        style="?android:attr/borderlessButtonStyle"
                        android:id="@+id/btn_zone_edit"
                        android:drawableTop="@drawable/ic_edit_24"
                        android:text="@string/edit"
                        android:padding="@dimen/buttonCardViewPadding"/>

                    <Button
                        android:layout_width="0dp"
                        android:layout_height="@dimen/imageButtonCardView"
                        android:layout_weight="1"
                        android:layout_gravity="center_horizontal|center|center_vertical"
                        android:background="@color/colorPrimary"
                        android:textAppearance="@style/TextAppearance.AppCompat.Widget.Button.Inverse"
                        style="?android:attr/borderlessButtonStyle"
                        android:padding="@dimen/buttonCardViewPadding"
                        android:id="@+id/btn_zone_delete"
                        android:drawableTop="@drawable/ic_delete_24"
                        android:text="@string/delete"/>

                </LinearLayout>

            </LinearLayout>

        </LinearLayout>

    </android.support.v7.widget.CardView>
</layout>

其余设置与基本示例中的相同。 只是坚持如何从列表中更新区域。

Answer 1

在删除/更新单击时，您将需要更新您的模型（您的存储库）。 存储库将发出一个新的LiveData项，适配器将被更新， DiffUtils将完成它的工作。 它将删除或更新该项目。

例如删除操作：

• 将单击侦听器设置为“删除”按钮
• 从监听器调用viewModel.deleteItem(id) （这是你的ZoneListViewModel ）
• 在ViewModel调用repository.deleteItem(id)
• 在存储库中使用Room来删除项目
• Room将使用更新的列表（没有已删除的项目）发出新值。
• 适配器会观察此列表，并与DiffUtils一起删除该项目。

这是android-architecture-blueprints的一个例子