我可以在Recyclerview中使用光标适配器与GridView

Question

我正在构建带有描述链接的图片应用程序。使用光标适配器的GridView RecyclerView是否是使用电影数据库作为电影缩略图和描述数据的来源的合适方法。

Answer 1

请在下面的链接中找到光标适配器实现，我还将代码放在链接下方，它可能会帮助您。

带有光标适配器的回收器视图

首先，CursorAdapter并非设计用于回收即可使用。您正在尝试破解某些永远无法正常工作的东西。您不能只称其为方法，并期望它正常运行。请参阅来源。

所以首先是第一件事。我们想使用光标。.让我们摆脱此责任并创建RecyClerViewCursorAdapter。这就是它所说的，用于回收模型。此细节几乎与Cursoradapter的工作方式相同。查看其来源以查看什么是相同的。

接下来，我们现在拥有您的原始类RVADAPTER来实现抽象的RecyClerViewCursorAdapter，该cursoradapter要求我们实现increateviewholder和我们的新OnBindViewHolder，该持有人为我们提供了一个光标参数以绑定。这些观点的详细信息与您的原始内容相同。

rvadapter.java

import android.content.Context;
import android.database.Cursor;
import android.net.Uri;
import android.support.v7.widget.CardView;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import com.squareup.picasso.Picasso;
import java.util.Random;

public class RVAdapter extends RecyclerViewCursorAdapter<RVAdapter.ProductViewHolder>
{
    private static final String TAG = RVAdapter.class.getSimpleName();
    private final Context mContext;
    private final Random mRandom;

    public RVAdapter(Context context, String locationSetting)
    {
        super(null);
        mContext = context;
        mRandom  = new Random(System.currentTimeMillis());
        // Sort order:  Ascending, by date.
        String sortOrder = ProductContract.ProductEntry.COLUMN_DATE + " ASC";
        Uri productForLocationUri = ProductContract.ProductEntry
            .buildProductLocationWithStartDate(locationSetting, System.currentTimeMillis());
        // Students: Uncomment the next lines to display what what you stored in the bulkInsert
        Cursor cursor = mContext.getContentResolver()
            .query(productForLocationUri, null, null, null, sortOrder);
        swapCursor(cursor);
    }
    @Override
    public ProductViewHolder onCreateViewHolder(ViewGroup parent, int viewType)
    {
        View view = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.item, parent, false);
        return new ProductViewHolder(view);
    }
    @Override
    protected void onBindViewHolder(ProductViewHolder holder, Cursor cursor)
    {
        String imagePath = cursor.getString(ShopFragment.COL_PRODUCT_IMAGE);
        String price = cursor.getString(ShopFragment.COL_PRODUCT_PRICE);
        holder.productPrice.setText("US $" + price);
        int height = mRandom.nextInt(50) + 500;
        //Download image using picasso library
        Picasso.with(mContext)
            .load(imagePath)
            .resize(500, height)
            .error(R.drawable.placeholder)
            .placeholder(R.drawable.placeholder)
            .into(holder.productPhoto);
    }

    public static class ProductViewHolder extends RecyclerView.ViewHolder
    {
        CardView cv;
        TextView productPrice;
        ImageView productPhoto;
        ProductViewHolder(View itemView)
        {
            super(itemView);
            cv = (CardView) itemView.findViewById(R.id.cv);
            productPrice = (TextView) itemView.findViewById(R.id.product_price);
            productPhoto = (ImageView) itemView.findViewById(R.id.product_photo);
        }
    }
}

recyClerviewCursorAdapter.java

import android.database.Cursor;
import android.database.DataSetObserver;
import android.support.v7.widget.RecyclerView;
import android.view.ViewGroup;

/**
 * RecyclerView CursorAdapter
 * <p>
 * Created by Simon on 28/02/2016.
 */
public abstract class RecyclerViewCursorAdapter<VH extends RecyclerView.ViewHolder> extends
    RecyclerView.Adapter<VH>
{
    private Cursor mCursor;
    private boolean mDataValid;
    private int mRowIDColumn;

    public RecyclerViewCursorAdapter(Cursor cursor)
    {
        setHasStableIds(true);
        swapCursor(cursor);
    }
    public abstract VH onCreateViewHolder(ViewGroup parent, int viewType);
    protected abstract void onBindViewHolder(VH holder, Cursor cursor);
    @Override
    public void onBindViewHolder(VH holder, int position)
    {
        if(!mDataValid){
            throw new IllegalStateException("this should only be called when the cursor is valid");
        }
        if(!mCursor.moveToPosition(position)){
            throw new IllegalStateException("couldn't move cursor to position " + position);
        }
        onBindViewHolder(holder, mCursor);
    }
    @Override
    public long getItemId(int position)
    {
        if(mDataValid && mCursor != null && mCursor.moveToPosition(position)){
            return mCursor.getLong(mRowIDColumn);
        }
        return RecyclerView.NO_ID;
    }
    @Override
    public int getItemCount()
    {
        if(mDataValid && mCursor != null){
            return mCursor.getCount();
        }
        else{
            return 0;
        }
    }
    protected Cursor getCursor()
    {
        return mCursor;
    }
    public void changeCursor(Cursor cursor)
    {
        Cursor old = swapCursor(cursor);
        if(old != null){
            old.close();
        }
    }
    public Cursor swapCursor(Cursor newCursor)
    {
        if(newCursor == mCursor){
            return null;
        }
        Cursor oldCursor = mCursor;
        if(oldCursor != null){
            if(mDataSetObserver != null){
                oldCursor.unregisterDataSetObserver(mDataSetObserver);
            }
        }
        mCursor = newCursor;
        if(newCursor != null){
            if(mDataSetObserver != null){
                newCursor.registerDataSetObserver(mDataSetObserver);
            }
            mRowIDColumn = newCursor.getColumnIndexOrThrow("_id");
            mDataValid = true;
            notifyDataSetChanged();
        }
        else{
            mRowIDColumn = -1;
            mDataValid = false;
            notifyDataSetChanged();
        }
        return oldCursor;
    }

    private DataSetObserver mDataSetObserver = new DataSetObserver()
    {
        @Override
        public void onChanged()
        {
            mDataValid = true;
            notifyDataSetChanged();
        }
        @Override
        public void onInvalidated()
        {
            mDataValid = false;
            notifyDataSetChanged();
        }
    };
}