java - 将 RecyclerView 转换为 ViewPager/PagerAdapter

Question

背景 - Android 新手，但对于移动布局相当漂亮，了解 Java、Kotlin 和 XML。然而这个任务似乎远远超出了我的能力范围。

问题 - 我希望将以下 Java 文件 (RecyclerView) 转换为 Kotlin 文件 (ViewPager) - 因为我已经有一个 ViewPager 连接了所需的相同滚动行为。我的印象是，对于经验丰富的开发人员来说，这只是 10 分钟的工作。如果是这种情况，我想知道是否可以寻求社区的帮助？至少要弄清楚从哪里开始。我似乎找不到有关如何将 RecyclerView 转换为 PagerAdapter 或 ViewPager 的指南。

本质上，我正在使用的现有 ViewPager 具有静态数据(5 个项目)，而这个可能有数十个项目，因此需要使用单独的数据源(CardItem 的项目)进行动态化。

<小时/>

RecyclerViewAdapter - 当前(Java)

package com.APPNAME.fragments.cards;
import android.databinding.DataBindingUtil;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import java.util.ArrayList;
import com.APPNAME.R;
import com.APPNAME.databinding.FragmentCardsRecentlyViewedBinding;
import com.APPNAME.model.cardItem.CardItem;



public class RecentlyViewedAdapter extends RecyclerView.Adapter<RecentlyViewedAdapter.RecentlyViewedViewHolder> {

    public OnCardClicked listener;
    private ArrayList<CardItem> items = new ArrayList<>();

    public void addItems(ArrayList<CardItem> list) {
        items = list;
        notifyDataSetChanged();
    }

    @Override
    public RecentlyViewedViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        FragmentCardsRecentlyViewedBinding binding = DataBindingUtil.inflate(LayoutInflater.from(parent.getContext()), R.layout.fragment_cards_recently_viewed, parent, false);
        return new RecentlyViewedViewHolder(binding);
    }

    @Override
    public void onBindViewHolder(RecentlyViewedViewHolder holder, int position) {
        holder.binding.setViewModel(new RecentlyViewedViewModel(items.get(position)));
    }

    @Override
    public int getItemCount() {
        return items.size();
    }

    interface OnCardClicked {
        void onCardClicked(View view, CardItem cardItem);
    }

    class RecentlyViewedViewHolder extends RecyclerView.ViewHolder {
        FragmentCardsRecentlyViewedBinding binding;

        public RecentlyViewedViewHolder(FragmentCardsRecentlyViewedBinding itemView) {
            super(itemView.getRoot());
            binding = itemView;
            binding.cardView.setOnClickListener(v -> {
                if (listener != null) {
                    listener.onCardClicked(v, items.get(getAdapterPosition()));
                }
            });
        }
    }
}

ViewPagerAdapter - future (Kotlin)

package com.APPNAME.fragments.cards
import android.support.annotation.DrawableRes
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import java.util.*
import kotlinx.android.synthetic.main.fragment_cards_recently_viewed.view.*
import com.APPNAME.R
import com.APPNAME.activities.BaseActivity
import com.APPNAME.activities.cards.NewCardActivity
import com.APPNAME.model.cardItem.CardItem
import com.APPNAME.views.wrapContentViewPager.ObjectAtPositionPagerAdapter


class RecentlyViewedItemAdapter constructor(private val activity: BaseActivity) : ObjectAtPositionPagerAdapter() {

    private var items = ArrayList<CardItem>()

    override fun instantiateItemObject(container: ViewGroup, position: Int) : Any {
    return getImageView(container, R.drawable.placeholder_card_image) { NewCardActivity.start(activity, it) }
    }

    private fun getImageView(container: ViewGroup, @DrawableRes imageResourceId: Int, onClick: (imageResourceId: Int) -> Unit = {}): View {
    val layoutInflater = LayoutInflater.from(container.context)
        val layout = layoutInflater.inflate(R.layout.fragment_cards_recently_viewed, container, false)
        val image = layout.recentlyViewedImage
        image.setImageResource(imageResourceId)
        image.setOnClickListener { onClick(imageResourceId) }
        container.addView(layout)
        return layout
    }

    override fun isViewFromObject(view: View, anObject: Any) = (view == anObject)
    override fun getCount() = 5     //Placeholder

    override fun destroyItemObject(container: ViewGroup, position: Int, view: Any) {
        container.removeView(view as View)
    }
}

Answer 1

如果您有相对较多的项目并且需要回收 View ，那么 RecyclerView 是您的正确选择。这肯定比创建具有固定项目计数和 View 持有者模式的自定义 View 寻呼机适配器更容易。默认/通用 PageAdapter 不会回收任何东西 - 添加它是为了确保您已启动所有 View 并准备好进行滑动。但是，您可以使用 https://developer.android.com/reference/android/support/v4/app/FragmentStatePagerAdapter.html当不再使用或重复使用时，这将销毁/重新创建 fragment 。