java - RecyclerView 空指针异常

Question

我是 Android Studio 的新手，发现了类似的问题，但没有一个回复适用于我当前的实例。我一直在尝试使用 RecyclerViews，但每当我用它打开一个 Activity 时，都会收到以下错误消息。代码未显示任何错误。

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.lucasrizzotto.edgeweather/com.lucasrizzotto.edgeweather.ui.HourlyForecastActivity}: 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

这是我的适配器:

public class HourAdapter extends RecyclerView.Adapter<HourAdapter.HourViewHolder> {

    private Hour[] mHours;

    public HourAdapter(Hour[] hours) {
        mHours = hours;
    }

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

    @Override
    public void onBindViewHolder(HourViewHolder holder, int position) {
        holder.bindHour(mHours[position]);
    }

    @Override
    public int getItemCount() {
        return mHours.length;
    }

    public class HourViewHolder extends RecyclerView.ViewHolder {

        public TextView mTimeLabel;
        public TextView mTemperatureLabel;
        public TextView mSummaryLabel;
        public ImageView mIconImageView;

        public HourViewHolder(View itemView) {
            super(itemView);
            mTimeLabel = (TextView) itemView.findViewById(R.id.timeLabel);
            mTemperatureLabel = (TextView) itemView.findViewById(R.id.temperatureLabel);
            mSummaryLabel = (TextView) itemView.findViewById(R.id.summaryLabel);
            mIconImageView = (ImageView) itemView.findViewById(R.id.iconImageView);
        }

        public void bindHour(Hour hour) {
            mTimeLabel.setText(hour.getHour());
            mSummaryLabel.setText(hour.getSummary());
            mTemperatureLabel.setText((int)hour.getTemperature());
            mIconImageView.setImageResource(hour.getIconId());
        }

    }
}

还有我的 Activity 类(请记住，我正在使用 ButterKnife 插件来避免样板代码)

public class HourlyForecastActivity extends AppCompatActivity {

    private Hour[] mHours;

    @BindView(R.id.recyclerView) RecyclerView mRecyclerView;

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

        Intent intent = getIntent();
        Parcelable[] parcelables = intent.getParcelableArrayExtra(MainActivity.HOURLY_FORECAST);
        mHours = Arrays.copyOf(parcelables, parcelables.length, Hour[].class);

        HourAdapter adapter = new HourAdapter(mHours);
        mRecyclerView.setAdapter(adapter);

        RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(this);
        mRecyclerView.setLayoutManager(layoutManager);
        mRecyclerView.setHasFixedSize(true);

    }
}

我忽略了什么？

提前感谢您的智慧!

Answer 1

尝试调用:

ButterKnife.bind(this);

设置内容 View 后

由于您不是以常规方式执行此操作，因此您需要实际调用 bind()。