在回收视图应用程序上设置视图适配器

vdgimpew  于 2021-08-25  发布在  Java
关注(0)|答案(1)|浏览(318)

我正在尝试构建一个用于学习如何使用recycleview和适配器的最小应用程序，当我设置适配器时，我的应用程序在没有任何日志记录的情况下崩溃。代码如下：

  1. package com.example.cafe.toplevel;
  3. import android.content.Context;
  4. import android.os.Bundle;
  5. import androidx.fragment.app.Fragment;
  6. import android.view.LayoutInflater;
  7. import android.view.View;
  8. import android.view.ViewGroup;
  9. import androidx.recyclerview.widget.GridLayoutManager;
  10. import androidx.recyclerview.widget.LinearLayoutManager;
  11. import androidx.recyclerview.widget.RecyclerView;
  12. import com.example.cafe.R;
  14. import java.util.ArrayList;
  15. import java.util.List;
  17. public class TopLevelFragment extends Fragment {
  19.     private static final String ARG_COLUMN_COUNT = "column-count";
  20.     private int mColumnCount = 1;
  22.     public TopLevelFragment() {
  23.         // Required empty public constructor
  24.     }
  26.     @SuppressWarnings("unused")
  27.     public static TopLevelFragment newInstance(int columnCount) {
  28.         TopLevelFragment fragment = new TopLevelFragment();
  29.         Bundle args = new Bundle();
  30.         args.putInt(ARG_COLUMN_COUNT, columnCount);
  31.         return fragment;
  32.     }
  34.     @Override
  35.     public void onCreate(Bundle savedInstanceState) {
  36.         super.onCreate(savedInstanceState);
  38.         if (getArguments() != null) {
  39.             mColumnCount = getArguments().getInt(ARG_COLUMN_COUNT);
  40.         }
  41.     }
  43.     @Override
  44.     public View onCreateView(LayoutInflater inflater, ViewGroup container,
  45.                              Bundle savedInstanceState) {
  46.         // Inflate the layout for this fragment
  47.         View view = inflater.inflate(R.layout.fragment_top_level, container, false);
  48.         List<CategoryRecyclerViewAdapter.CategoryItem> items = new ArrayList<>();
  49.         items.add(new CategoryRecyclerViewAdapter.CategoryItem("1", "Drinks"));
  50.         items.add(new CategoryRecyclerViewAdapter.CategoryItem("2", "Food"));
  51.         CategoryRecyclerViewAdapter categoryRecyclerViewAdapter = new CategoryRecyclerViewAdapter(items);
  52.         RecyclerView recyclerView = view.findViewById(R.id.category_list);
  53.         Context context = view.getContext();
  54.         if (mColumnCount <= 1) {
  55.             recyclerView.setLayoutManager(new LinearLayoutManager(context));
  56.         } else {
  57.             recyclerView.setLayoutManager(new GridLayoutManager(context, mColumnCount));
  58.         }
  59.         recyclerView.setAdapter(categoryRecyclerViewAdapter);
  60.         return view;
  61.     }
  62. }

如果您能帮助解决此问题，我们将不胜感激。
编辑：根据请求，我已包含适配器的代码：

  1. package com.example.cafe.toplevel;
  3. import android.view.LayoutInflater;
  4. import android.view.View;
  5. import android.view.ViewGroup;
  6. import android.widget.TextView;
  7. import androidx.recyclerview.widget.RecyclerView;
  8. import com.example.cafe.R;
  10. import java.util.List;
  12. public class CategoryRecyclerViewAdapter extends RecyclerView.Adapter<CategoryRecyclerViewAdapter.ViewHolder> {
  13.     public static class CategoryItem {
  14.         String name;
  15.         String id;
  17.         public CategoryItem(String id, String name) {
  18.             this.id = id;
  19.             this.name = name;
  20.         }
  21.     }
  23.     private final List<CategoryItem> mValues;
  25.     public CategoryRecyclerViewAdapter(List<CategoryItem> items) {
  26.         mValues = items;
  27.     }
  29.     @Override
  30.     public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
  31.         View view = LayoutInflater.from(parent.getContext())
  32.                 .inflate(R.layout.fragment_top_level, parent, false);
  33.         return new ViewHolder(view);
  34.     }
  36.     @Override
  37.     public void onBindViewHolder(final ViewHolder holder, int position) {
  38.         holder.mItem = mValues.get(position);
  39.         holder.mIdView.setText(mValues.get(position).id);
  40.         holder.mContentView.setText(mValues.get(position).name);
  41.     }
  43.     @Override
  44.     public int getItemCount() {
  45.         return mValues.size();
  46.     }
  48.     public class ViewHolder extends RecyclerView.ViewHolder {
  49.         public final View mView;
  50.         public final TextView mIdView;
  51.         public final TextView mContentView;
  52.         public CategoryItem mItem;
  54.         public ViewHolder(View view) {
  55.             super(view);
  56.             mView = view;
  57.             mIdView = (TextView) view.findViewById(R.id.category_id);
  58.             mContentView = (TextView) view.findViewById(R.id.category_name);
  59.         }
  61.         @Override
  62.         public String toString() {
  63.             return super.toString() + " '" + mContentView.getText() + "'";
  64.         }
  65.     }
  66. }

添加日志错误：

  1. 2021-07-07 22:36:02.916 13387-13387/com.example.cafe E/AndroidRuntime: FATAL EXCEPTION: main
  2.     Process: com.example.cafe, PID: 13387
  3.     java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
  4.         at com.example.cafe.toplevel.CategoryRecyclerViewAdapter.onBindViewHolder(CategoryRecyclerViewAdapter.java:42)
  5.         at com.example.cafe.toplevel.CategoryRecyclerViewAdapter.onBindViewHolder(CategoryRecyclerViewAdapter.java:13)
  6.         at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7254)
  7.         at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7337)
  8.         at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6194)
  9.         at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6460)
  10.         at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6300)
  11.         at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6296)
  12.         at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2330)
  13.         at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1631)
  14.         at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1591)
  15.         at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:668)
  16.         at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4309)
  17.         at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:4012)
  18.         at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4578)
  19.         at android.view.View.layout(View.java:22844)
  20.         at android.view.ViewGroup.layout(ViewGroup.java:6389)
  21.         at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
  22.         at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
  23.         at android.view.View.layout(View.java:22844)
  24.         at android.view.ViewGroup.layout(ViewGroup.java:6389)
  25.         at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1855)
  26.         at android.view.View.layout(View.java:22844)
  27.         at android.view.ViewGroup.layout(ViewGroup.java:6389)
  28.         at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
  29.         at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
  30.         at android.view.View.layout(View.java:22844)
  31.         at android.view.ViewGroup.layout(ViewGroup.java:6389)
  32.         at androidx.appcompat.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:536)
  33.         at android.view.View.layout(View.java:22844)
  34.         at android.view.ViewGroup.layout(ViewGroup.java:6389)
  35.         at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
  36.         at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
  37.         at android.view.View.layout(View.java:22844)
  38.         at android.view.ViewGroup.layout(ViewGroup.java:6389)
  39.         at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
  40.         at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
  41.         at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
  42.         at android.view.View.layout(View.java:22844)
  43.         at android.view.ViewGroup.layout(ViewGroup.java:6389)
  44.         at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
  45.         at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
  46.         at com.android.internal.policy.DecorView.onLayout(DecorView.java:784)
  47.         at android.view.View.layout(View.java:22844)
  48.         at android.view.ViewGroup.layout(ViewGroup.java:6389)
  49.         at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3475)
  50.         at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2943)
  51.         at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1948)
  52.         at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8177)
  53.         at android.view.Choreographer$CallbackRecord.run(Choreographer.java:972)
  54.         at android.view.Choreographer.doCallbacks(Choreographer.java:796)
  55.         at android.view.Choreographer.doFrame(Choreographer.java:731)
  56. 2021-07-07 22:36:02.916 13387-13387/com.example.cafe E/AndroidRuntime:     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:957)
  57.         at android.os.Handler.handleCallback(Handler.java:938)
  58.         at android.os.Handler.dispatchMessage(Handler.java:99)
  59.         at android.os.Looper.loop(Looper.java:223)
  60.         at android.app.ActivityThread.main(ActivityThread.java:7664)
  61.         at java.lang.reflect.Method.invoke(Native Method)
  62.         at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
  63.         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
Javaandroidandroid-recyclerview

1条答案

按热度按时间
ifmq2ha2

ifmq2ha21#

你的代码不正确。您正在使用充气布局并将其投射到recyclerview。

  1. if (view instanceof RecyclerView) {
  2.     Context context = view.getContext();
  3.     RecyclerView recyclerView = (RecyclerView) view;
  4.     if (mColumnCount <= 1) {
  5.         recyclerView.setLayoutManager(new LinearLayoutManager(context));
  6.     } else {
  7.         recyclerView.setLayoutManager(new GridLayoutManager(context, mColumnCount));
  8.     }
  9.     recyclerView.setAdapter(categoryRecyclerViewAdapter); // commenting this prevents crash but it also doesn't render the list
  10. }

你应该在recyclerview上使用它。 findViewById 回收视图的一部分。然后，您将能够在该recyclerview上设置适配器。
此外，您为列表编写的语法不正确。不要为arraylist保留空泛型。这是不可取的。

  1. List<CategoryRecyclerViewAdapter.CategoryItem> items = new ArrayList<>();
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