我有一个数据库，我正在尝试在我的应用程序的cardview上显示列。 我猜数据库方面没有错。我已经检查过了，例如可以将项目添加到数据库中。我可以登录注册。但是，当我添加项目时，添加过程完成后，我应该会在Cardview中看到它们。 当我在数据库上添加项目时，它返回到recyclerview布局，但什么也不显示。只有一个空白页。
到目前为止，调试过程中没有错误。
这是我的Cardview布局：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:orientation="vertical"
android:padding="15dp"
android:layout_height="wrap_content">
<android.support.v7.widget.CardView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="5dp"
android:layout_marginBottom="5dp"
android:layout_marginLeft="5dp"
android:layout_marginRight="5dp">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
android:padding="5dp">
<TextView
android:id="@+id/itemName"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Stock Name"
android:textColor="@color/colorPrimary" />
<TextView
android:id="@+id/barcode"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Stock Code" />
<TextView
android:id="@+id/tvQuantity"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Quantity" />
<TextView
android:id="@+id/tvPrice"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Price" />
<TextView
android:id="@+id/tvCost"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Cost" />
</LinearLayout>
</LinearLayout>
</android.support.v7.widget.CardView>
</LinearLayout>
recyclerlayout：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
>
<android.support.v7.widget.RecyclerView
android:id="@+id/recyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</LinearLayout>
RECYCLER.JAVA
public class recycler extends AppCompatActivity {
private RecyclerView mRecyclerView;
private RecyclerView.LayoutManager mLayoutManager;
private DatabaseHelper myDb;
private itemAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_recycler);
myDb = new DatabaseHelper(this);
Intent intent =getIntent();
mRecyclerView = (RecyclerView)findViewById(R.id.recyclerView);
mRecyclerView.setHasFixedSize(true);
// use a linear layout manager
mLayoutManager = new LinearLayoutManager(this);
mRecyclerView.setLayoutManager(mLayoutManager);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.home_menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle item selection
switch (item.getItemId()) {
case R.id.addMenu:
goToAddActivity();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
private void goToAddActivity(){
Intent intent = new Intent(recycler.this, add.class);
startActivity(intent);
}
}
itemAdapter.java
public class itemAdapter extends RecyclerView.Adapter<itemAdapter.ViewHolder> {
private List<list> mItemsList;
private Context mContext; //to inflate list layout
private RecyclerView mRecyclerV;
public class ViewHolder extends RecyclerView.ViewHolder{
public TextView nameTxt;
public TextView quantityTxt;
public TextView priceTxt;
public TextView costTxt;
public TextView barcodeTxt;
public View layout;
public ViewHolder( View v) {
super(v);
layout = v;
nameTxt = (TextView) v.findViewById(R.id.itemName);
quantityTxt = (TextView) v.findViewById(R.id.tvQuantity);
priceTxt = (TextView) v.findViewById(R.id.tvPrice);
costTxt = (TextView) v.findViewById(R.id.tvCost);
barcodeTxt = (TextView) v.findViewById(R.id.barcode);
}
}
public void add(int position, list list) {
mItemsList.add(position, list);
notifyItemInserted(position);
}
public void remove(int position) {
mItemsList.remove(position);
notifyItemRemoved(position);
}
// Provide a suitable constructor (depends on the kind of dataset)
public itemAdapter(List<list> myDataset, Context context, RecyclerView recyclerView) {
mItemsList = myDataset;
mContext = context;
mRecyclerV = recyclerView;
}
// Create new views (invoked by the layout manager)
@Override
public itemAdapter.ViewHolder onCreateViewHolder( ViewGroup parent, int viewType) {
//create a new view
LayoutInflater inflater = LayoutInflater.from(parent.getContext());
View v =inflater.inflate(R.layout.activity_list, parent, false);
// set the view's size, margins, paddings and layout parameters
return new ViewHolder(v);
}
// Replace the contents of a view (invoked by the layout manager)
@Override
public void onBindViewHolder(ViewHolder holder, final int position) {
// - get element from your dataset at this position
// - replace the contents of the view with that element
final list list = mItemsList.get(position);
holder.nameTxt.setText("Stock Name: " + list.getName());
holder.barcodeTxt.setText("Barcode: " + list.getBarcode());
holder.quantityTxt.setText("Quantity: " + list.getQuantity());
holder.priceTxt.setText("Price: " + list.getPrice());
holder.costTxt.setText("Cost: " + list.getCost());
holder.layout.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
AlertDialog.Builder builder = new AlertDialog.Builder(mContext);
builder.setTitle("Choose option");
builder.setMessage("Update or delete stock?");
builder.setPositiveButton("Update", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
//go to update activity
goToUpdateActivity(list.getId());
}
});
builder.setNeutralButton("Delete", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
DatabaseHelper dbHelper = new DatabaseHelper(mContext);
dbHelper.deleteRecord(list.getId(), mContext);
mItemsList.remove(position);
mRecyclerV.removeViewAt(position);
notifyItemRemoved(position);
notifyItemRangeChanged(position, mItemsList.size());
notifyDataSetChanged();
}
});
builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
}
});
builder.create().show();
}
});
}
private void goToUpdateActivity(long listID){
Intent goToUpdate = new Intent(mContext, update.class);
goToUpdate.putExtra("listID", listID);
mContext.startActivity(goToUpdate);
}
@Override
public int getItemCount() {
return mItemsList.size();
}
}