我正在构建带有描述链接的图片应用程序。具有Cursor适配器的GridView RecyclerView是否适合作为执行此操作的方法,因为使用Movie数据库作为电影缩略图和描述数据的源。
最佳答案
请在下面的链接中找到游标适配器的实现,我也将代码放在下面的链接中,可能会对您有所帮助。
Recycler view with cursor adapter
首先,CursorAdapter不适用于RecyclerView。您正在尝试破解永远无法正常工作的内容。您不能只调用它的方法并期望它正确运行。参见源。
所以第一件事。我们要使用游标..让我们分开这个责任,并创建RecyclerViewCursorAdapter。它就是说的,一个用于RecyclerView的CursorAdapter。其细节与CursorAdapter的工作原理几乎相同。查看其来源以了解什么是相同的,什么不是。
接下来,我们现在有了您的原始类RVAdapter,以实现抽象的RecyclerViewCursorAdapter,这要求我们实现onCreateViewHolder和新的onBindViewHolder,后者给我们提供了一个Cursor参数进行绑定。这些视图的细节与您整理的原始视图相同。
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();
}
};
}