car/widget/ListItem.java

package androidx.car.widget;

import android.car.drivingstate.CarUxRestrictions;
import android.support.annotation.CallSuper;
import android.support.annotation.Nullable;
import android.support.annotation.StyleRes;
import android.support.v7.widget.RecyclerView;
import android.view.View;

import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;

import androidx.car.R;

/**
 * Definition of items that can be inserted into {@link ListItemAdapter}.
 *
 * @param  ViewHolder that extends {@link ListItem.ViewHolder}.
 */
public abstract class ListItem<VH extends ListItem.ViewHolder> {

    // Whether the item should calculate view layout params. This usually happens when the item is
    // updated after bind() is called. Calling bind() resets to false.
    private boolean mDirty;

    // Tag for indicating whether to hide the divider.
    private boolean mHideDivider;

    private final List<ViewBinder<VH>> mCustomBinders = new ArrayList<>();
    // Stores ViewBinders to revert customization. Does not guarantee to 1:1 match ViewBinders
    // in mCustomerBinders.
    private final List<ViewBinder<VH>> mCustomBinderCleanUps = new ArrayList<>();

    @StyleRes private int mTitleTextAppearance = R.style.TextAppearance_Car_Body1;
    @StyleRes private int mBodyTextAppearance = R.style.TextAppearance_Car_Body2;

    /**
     * Classes that extends {@code ListItem} should register its view type in
     * {@link ListItemAdapter#registerListItemViewType(int, int, Function)}.
     *
     * @return type of this ListItem.
     */
    abstract int getViewType();

    /**
     * Called when ListItem is bound to its ViewHolder.
     */
    final void bind(VH viewHolder) {
        // Attempt to clean up custom view binder from previous item (if any).
        // Then save the clean up binders for next item.
        viewHolder.cleanUp();
        for (ViewBinder cleanUp : mCustomBinderCleanUps) {
            viewHolder.addCleanUp(cleanUp);
        }

        if (isDirty()) {
            resolveDirtyState();
            markClean();
        }
        onBind(viewHolder);

        // Custom view binders are applied after view layout.
        for (ViewBinder<VH> binder: mCustomBinders) {
            binder.bind(viewHolder);
        }
    }

    /** Sets the title text appearance from the specified style resource. */
    @CallSuper
    void setTitleTextAppearance(@StyleRes int titleTextAppearance) {
        mTitleTextAppearance = titleTextAppearance;
    }

    /** Sets the body text appearance from the specified style resource. */
    @CallSuper
    void setBodyTextAppearance(@StyleRes int bodyTextAppearance) {
        mBodyTextAppearance = bodyTextAppearance;
    }

    /** Returns the text appearance that should be used for title text. */
    @StyleRes
    final int getTitleTextAppearance() {
        return mTitleTextAppearance;
    }

    /** Returns the text appearance that should be used for body text. */
    @StyleRes
    final int getBodyTextAppearance() {
        return mBodyTextAppearance;
    }


    /**
     * Marks this item as dirty so {@link #resolveDirtyState()} is required in next bind() call.
     *
     * <p>This method should be called in each setter.
     */
    protected void markDirty() {
        mDirty = true;
    }

    /**
     * Marks this item as not dirty. No need to call {@link #resolveDirtyState()} in next bind().
     */
    protected void markClean() {
        mDirty = false;
    }

    /**
     * @return {@code true} if next bind() should call {@link #resolveDirtyState()}.
     */
    protected boolean isDirty() {
        return mDirty;
    }

    /**
     * Whether hide the item divider coming after this {@code ListItem}.
     *
     * <p>Note: For this to work, one must invoke
     * {@code PagedListView.setDividerVisibilityManager(adapter} for {@link ListItemAdapter} and
     * have dividers enabled on {@link PagedListView}.
     */
    public void setHideDivider(boolean hideDivider) {
        mHideDivider = hideDivider;
        markDirty();
    }

    /**
     * @return {@code true} if the divider that comes after this ListItem should be hidden.
     * Defaults to false.
     */
    public boolean shouldHideDivider() {
        return mHideDivider;
    };


    /**
     * Does the work that moves the ListItem from dirty state to clean state, i.e. the work required
     * the first time this ListItem {@code bind}s to {@link ListItem.ViewHolder}.
     * This method will transition ListItem to clean state. ListItem in clean state should move to
     * dirty state when it is modified by calling {@link #markDirty()}.
     */
    protected abstract void resolveDirtyState();

    /**
     * Binds this ListItem to {@code viewHolder} by applying data in ListItem to sub-views.
     * Assume {@link ViewHolder#cleanUp()} has already been invoked.
     */
    protected abstract void onBind(VH viewHolder);

    /**
     * Same as {@link #addViewBinder(ViewBinder, ViewBinder)} when {@code cleanUp} ViewBinder
     * is null.
     *
     * @param binder to interact with subviews in {@code ViewHolder}.
     *
     * @see #addViewBinder(ViewBinder, ViewBinder)
     */
    public final void addViewBinder(ViewBinder<VH> binder) {
        addViewBinder(binder, null);
    }

    /**
     * Adds {@link ViewBinder} to interact with sub-views in {@link ViewHolder}. These ViewBinders
     * will always be applied after {@link #onBind(ViewHolder)}.
     *
     * <p>To interact with a foobar sub-view in {@code ViewHolder}, make sure to first set its
     * visibility, or call setFoobar() setter method.
     *
     * <p>Example:
     * <pre>
     * {@code
     * TextListItem item = new TextListItem(context);
     * item.setTitle("title");
     * item.addViewBinder((viewHolder) -> {
     *     viewHolder.getTitle().doFoobar();
     * }, (viewHolder) -> {
     *     viewHolder.getTitle().revertFoobar();
     * });
     * }
     * </pre>
     *
     * @params binder to interact with subviews in {@code ViewHolder}.
     * @params cleanUp view binder to revert the effect of {@code binder}. cleanUp binders will be
     *                 stored in {@link ListItem.ViewHolder} and should be invoked via
     *                 {@link ViewHolder#cleanUp()} before {@code ViewHolder} is recycled.
     *                 This is to avoid changed made to ViewHolder lingers around when ViewHolder is
     *                 recycled. Pass in null to skip.
     */
    public final void addViewBinder(ViewBinder<VH> binder, @Nullable ViewBinder<VH> cleanUp) {
        mCustomBinders.add(binder);
        if (cleanUp != null) {
            mCustomBinderCleanUps.add(cleanUp);
        }
        markDirty();
    }

    /**
     * Removes the first occurrence of the specified item.
     *
     * @param binder to be removed.
     * @return {@code true} if {@code binder} exists. {@code false} otherwise.
     */
    public boolean removeViewBinder(ViewBinder<VH> binder) {
        return mCustomBinders.remove(binder);
    }

    /**
     * Functional interface to provide a way to interact with views in {@code ViewHolder}.
     * {@code ListItem} calls all added ViewBinders when it {@code bind}s to {@code ViewHolder}.
     *
     * @param  class that extends {@link RecyclerView.ViewHolder}.
     */
    public interface ViewBinder<VH> {
        /**
         * Provides a way to interact with views in view holder.
         */
        void bind(VH viewHolder);
    }

    /**
     * ViewHolder that supports {@link ViewBinder}.
     */
    public abstract static class ViewHolder extends RecyclerView.ViewHolder {
        private final List<ViewBinder> mCleanUps = new ArrayList<>();

        public ViewHolder(View itemView) {
            super(itemView);
        }

        /**
         * Removes customization from previous ListItem. Intended to be used when this ViewHolder is
         * bound to a ListItem.
         */
        public final void cleanUp() {
            for (ViewBinder binder : mCleanUps) {
                binder.bind(this);
            }
        }

        /**
         * Stores clean up ViewBinders that will be called in {@code cleanUp()}.
         */
        public final void addCleanUp(@Nullable ViewBinder<ViewHolder> cleanUp) {
            if (cleanUp != null) {
                mCleanUps.add(cleanUp);
            }
        }

        /**
         * Update children views to comply with UX restriction changes.
         *
         * @param restrictions current car UX restrictions.
         */
        abstract void complyWithUxRestrictions(CarUxRestrictions restrictions);
    }
}