安卓程序运行含RecyclerView的页面时模拟器发生崩溃

问题相关材料 #

• RecyclerView页面布局截图：
• RecyclerView列表项布局截图：
• Logcat报错信息截图：

原始ViewHolder实现代码 #

public class myPageViewHolder extends RecyclerView.ViewHolder {

TextView rName, rDesc, rDuration, rIngredients, rSteps;

public myPageViewHolder(View itemView) {
    super(itemView);
    rName = itemView.findViewById(R.id.rName);
    rDesc = itemView.findViewById(R.id.rDesc);
    rDuration = itemView.findViewById(R.id.rDuration);
    rIngredients = itemView.findViewById(R.id.rIngredients);
    rSteps = itemView.findViewById(R.id.rSteps);
}
}

原始Adapter实现代码 #

public class myPageAdapter extends RecyclerView.Adapter<myPageViewHolder> {

ArrayList<Recipe> data;

public myPageAdapter(ArrayList<Recipe> input) { data = input; }

public myPageViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View item = LayoutInflater.from(parent.getContext()).inflate(R.layout.mypagelayout, parent, false);
    return new myPageViewHolder(item);
}

public void onBindViewHolder(myPageViewHolder holder, int position) {
    Recipe r = data.get(position);
    holder.rName.setText(r.getName());
    holder.rDesc.setText(r.getDescription());
    holder.rDuration.setText(r.getDuration() + "mins");
    holder.rIngredients.setText(r.getIngredients()[('\n')]);
    holder.rSteps.setText(r.getSteps()[('\n')]);
}

public int getItemCount() { return data.size(); }
}

// 粘贴错位的冗余代码
RecyclerView recyclerView = findViewById(R.id.recyclerView);
myPageAdapter adapter = new myPageAdapter(recipeList);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
recyclerView.setItemAnimator(new DefaultItemAnimator());
recyclerView.setAdapter(adapter);

原始MainActivity实现代码 #

public class MainActivity extends AppCompatActivity {

// 错误位置初始化列表数据
ArrayList<Recipe> recipeList = (ArrayList<Recipe>) getIntent().getSerializableExtra("rList");
Intent intent = getIntent();

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

    ImageView create = findViewById(R.id.createImage);

    create.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent gotoCreate = new Intent(MainActivity.this, createRecipe.class);
            startActivity(gotoCreate);
        }
    });

    RecyclerView recyclerView = findViewById(R.id.recyclerView);
    myPageAdapter adapter = new myPageAdapter(recipeList);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));
    recyclerView.setItemAnimator(new DefaultItemAnimator());
    recyclerView.setAdapter(adapter);
}
}

问题点逐一修复 #

1. 删除错位冗余代码
   Adapter类闭合大括号后的RecyclerView初始化代码是粘贴错误，直接删除即可，这段逻辑已经在MainActivity中实现，残留会直接触发编译错误。
2. 修正Intent取值时机
   禁止在Activity成员变量声明位置直接调用getIntent()，此时Activity未完成生命周期初始化，调用返回值为空，直接强转序列化列表会触发空指针崩溃。需要把取值逻辑移到onCreate方法内，同时加空值兜底，覆盖启动时未传参的边缘场景。
3. 修正数组取值逻辑错误
   onBindViewHolder中r.getIngredients()[('\n')]写法存在逻辑错误：'\n'是ASCII码为10的字符，作为数组索引会强制取数组第11个元素，只要数组长度不足就会触发数组越界崩溃。如果需要把数组元素用换行拼接为字符串，使用TextUtils.join("\n", 数组对象)实现即可。
4. 确认列表项布局引用正确
   检查onCreateViewHolder中inflate的R.layout.mypagelayout是否为单个列表项的布局文件，不要把放置RecyclerView的整个页面布局传进去，否则会因找不到对应ID的TextView触发空指针。

修正后可直接运行的代码 #

MainActivity部分 #

public class MainActivity extends AppCompatActivity {

private ArrayList<Recipe> recipeList;

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

    // 生命周期初始化完成后再取Intent参数
    Intent intent = getIntent();
    if (intent != null) {
        recipeList = (ArrayList<Recipe>) intent.getSerializableExtra("rList");
    }
    // 空值兜底避免空指针
    if (recipeList == null) {
        recipeList = new ArrayList<>();
    }

    ImageView create = findViewById(R.id.createImage);
    create.setOnClickListener(view -> {
        Intent gotoCreate = new Intent(MainActivity.this, createRecipe.class);
        startActivity(gotoCreate);
    });

    RecyclerView recyclerView = findViewById(R.id.recyclerView);
    myPageAdapter adapter = new myPageAdapter(recipeList);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));
    recyclerView.setItemAnimator(new DefaultItemAnimator());
    recyclerView.setAdapter(adapter);
}
}

Adapter onBindViewHolder修正部分 #

@Override
public void onBindViewHolder(myPageViewHolder holder, int position) {
    Recipe r = data.get(position);
    holder.rName.setText(r.getName());
    holder.rDesc.setText(r.getDescription());
    holder.rDuration.setText(r.getDuration() + "mins");
    holder.rIngredients.setText(TextUtils.join("\n", r.getIngredients()));
    holder.rSteps.setText(TextUtils.join("\n", r.getSteps()));
}

内容的提问来源于stack exchange，提问作者Kelven Lim