Question

在被告知使用RecyclerView而不是ListView之后，我尝试将其与SearchView一起实现。但是，我收到一个关于对象为null的奇怪错误：

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference

我目前有以下代码：

SearchActivity.java

package com.rickteuthof.strangejourneycompendium;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.widget.SearchView;

import java.util.ArrayList;

public class SearchActivity extends AppCompatActivity implements SearchView.OnQueryTextListener {

    public static ArrayList<String> demonNames;
    private SearchAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        RecyclerView r = findViewById(R.id.recyclerView);

        demonNames = MainActivity.demonNames;

        adapter = new SearchAdapter(this, demonNames);
        r.setLayoutManager(new LinearLayoutManager(getApplicationContext(), LinearLayoutManager.VERTICAL, false));
        r.setAdapter(adapter);

        SearchView s = findViewById(R.id.searchBar);
        s.setOnQueryTextListener(this);

    }

    @Override
    public boolean onQueryTextSubmit(String query) {

        return false;
    }

    @Override
    public boolean onQueryTextChange(String newText) {
        adapter.filter(newText);
        return false;
    }
}

SearchAdapter.java

package com.rickteuthof.strangejourneycompendium;
import android.content.Context;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.Locale;

public class SearchAdapter extends RecyclerView.Adapter<SearchAdapter.MyViewHolder> {

    private LayoutInflater inflater;
    private ArrayList<String> demonNames;
    private ArrayList<String> results;

    public SearchAdapter(Context ctx, ArrayList<String> demonNames){

        inflater = LayoutInflater.from(ctx);
        this.demonNames = demonNames;
        this.results = new ArrayList<String>();
        this.results.addAll(SearchActivity.demonNames);
    }

    @NonNull
    @Override
    public SearchAdapter.MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {

        View view = inflater.inflate(R.layout.recycler_item, parent, false);

        return new MyViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull SearchAdapter.MyViewHolder holder, int position) {

        holder.time.setText(demonNames.get(position));
    }

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

    class MyViewHolder extends RecyclerView.ViewHolder{

        TextView time;

        public MyViewHolder(View itemView) {
            super(itemView);

            time = itemView.findViewById(R.id.result);
        }

    }

    // Filter Class
    public void filter(String charText) {
        charText = charText.toLowerCase(Locale.getDefault());
        SearchActivity.demonNames.clear();
        if (charText.length() == 0) {
            SearchActivity.demonNames.addAll(results);
        } else {
            for (String wp : results) {
                if (wp.toLowerCase(Locale.getDefault()).contains(charText)) {
                    SearchActivity.demonNames.add(wp);
                }
            }
        }
        notifyDataSetChanged();
    }
}

我的数据集是一个名为demonNames的String数组，我尝试对其进行过滤以在RecyclerView中获得正确的结果。

这是我的xml布局：

activity_search.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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="match_parent"
    tools:context=".SearchActivity">

    <SearchView
        android:id="@+id/searchBar"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        app:layout_constraintBottom_toTopOf="@+id/recyclerView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.0" />

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/searchBar" >

    </android.support.v7.widget.RecyclerView>
</android.support.constraint.ConstraintLayout>

recycler_item.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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="match_parent">

    <TextView
        android:id="@+id/result"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginTop="16dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>

Answer 1

void OnMouseDown() { Debug.Log ("MOUSE DOWN"); } void OnMouseDrag() { typeBtnPos = typeBtn [typeSquare].transform.position; typeBtn [typeSquare].transform.position = new Vector2 (Input.mousePosition.x, Input.mousePosition.y); Debug.Log ("MOUSE"); } void OnMouseUp() { typeBtn [typeSquare].transform.position = typeBtnPos; Debug.Log ("MOUSE UP"); }

替换为

setContentView(R.layout.activity_main);

无法使RecyclerView正常工作

1 个答案: