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(284)

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：

package com.example.cafe.toplevel;

import android.content.Context;
import android.os.Bundle;
import androidx.fragment.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import androidx.recyclerview.widget.GridLayoutManager;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import com.example.cafe.R;

import java.util.ArrayList;
import java.util.List;

public class TopLevelFragment extends Fragment {

    private static final String ARG_COLUMN_COUNT = "column-count";
    private int mColumnCount = 1;

    public TopLevelFragment() {
        // Required empty public constructor
    }

    @SuppressWarnings("unused")
    public static TopLevelFragment newInstance(int columnCount) {
        TopLevelFragment fragment = new TopLevelFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_COLUMN_COUNT, columnCount);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if (getArguments() != null) {
            mColumnCount = getArguments().getInt(ARG_COLUMN_COUNT);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_top_level, container, false);
        List<CategoryRecyclerViewAdapter.CategoryItem> items = new ArrayList<>();
        items.add(new CategoryRecyclerViewAdapter.CategoryItem("1", "Drinks"));
        items.add(new CategoryRecyclerViewAdapter.CategoryItem("2", "Food"));
        CategoryRecyclerViewAdapter categoryRecyclerViewAdapter = new CategoryRecyclerViewAdapter(items);
        RecyclerView recyclerView = view.findViewById(R.id.category_list);
        Context context = view.getContext();
        if (mColumnCount <= 1) {
            recyclerView.setLayoutManager(new LinearLayoutManager(context));
        } else {
            recyclerView.setLayoutManager(new GridLayoutManager(context, mColumnCount));
        }
        recyclerView.setAdapter(categoryRecyclerViewAdapter);
        return view;
    }
}

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：

package com.example.cafe.toplevel;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.recyclerview.widget.RecyclerView;
import com.example.cafe.R;

import java.util.List;

public class CategoryRecyclerViewAdapter extends RecyclerView.Adapter<CategoryRecyclerViewAdapter.ViewHolder> {
    public static class CategoryItem {
        String name;
        String id;

        public CategoryItem(String id, String name) {
            this.id = id;
            this.name = name;
        }
    }

    private final List<CategoryItem> mValues;

    public CategoryRecyclerViewAdapter(List<CategoryItem> items) {
        mValues = items;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.fragment_top_level, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(final ViewHolder holder, int position) {
        holder.mItem = mValues.get(position);
        holder.mIdView.setText(mValues.get(position).id);
        holder.mContentView.setText(mValues.get(position).name);
    }

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

    public class ViewHolder extends RecyclerView.ViewHolder {
        public final View mView;
        public final TextView mIdView;
        public final TextView mContentView;
        public CategoryItem mItem;

        public ViewHolder(View view) {
            super(view);
            mView = view;
            mIdView = (TextView) view.findViewById(R.id.category_id);
            mContentView = (TextView) view.findViewById(R.id.category_name);
        }

        @Override
        public String toString() {
            return super.toString() + " '" + mContentView.getText() + "'";
        }
    }
}

添加日志错误：

2021-07-07 22:36:02.916 13387-13387/com.example.cafe E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.cafe, PID: 13387
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
        at com.example.cafe.toplevel.CategoryRecyclerViewAdapter.onBindViewHolder(CategoryRecyclerViewAdapter.java:42)
        at com.example.cafe.toplevel.CategoryRecyclerViewAdapter.onBindViewHolder(CategoryRecyclerViewAdapter.java:13)
        at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7254)
        at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7337)
        at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6194)
        at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6460)
        at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6300)
        at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6296)
        at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2330)
        at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1631)
        at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1591)
        at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:668)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4309)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:4012)
        at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4578)
        at android.view.View.layout(View.java:22844)
        at android.view.ViewGroup.layout(ViewGroup.java:6389)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
        at android.view.View.layout(View.java:22844)
        at android.view.ViewGroup.layout(ViewGroup.java:6389)
        at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1855)
        at android.view.View.layout(View.java:22844)
        at android.view.ViewGroup.layout(ViewGroup.java:6389)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
        at android.view.View.layout(View.java:22844)
        at android.view.ViewGroup.layout(ViewGroup.java:6389)
        at androidx.appcompat.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:536)
        at android.view.View.layout(View.java:22844)
        at android.view.ViewGroup.layout(ViewGroup.java:6389)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
        at android.view.View.layout(View.java:22844)
        at android.view.ViewGroup.layout(ViewGroup.java:6389)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
        at android.view.View.layout(View.java:22844)
        at android.view.ViewGroup.layout(ViewGroup.java:6389)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
        at com.android.internal.policy.DecorView.onLayout(DecorView.java:784)
        at android.view.View.layout(View.java:22844)
        at android.view.ViewGroup.layout(ViewGroup.java:6389)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3475)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2943)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1948)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8177)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:972)
        at android.view.Choreographer.doCallbacks(Choreographer.java:796)
        at android.view.Choreographer.doFrame(Choreographer.java:731)
2021-07-07 22:36:02.916 13387-13387/com.example.cafe E/AndroidRuntime:     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:957)
        at android.os.Handler.handleCallback(Handler.java:938)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7664)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        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。

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

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。

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