android中的空指针异常错误回收视图？

时间：2015-06-26 19:24:58

标签： java android android-recyclerview

所以我得到这个错误java.lang.NullPointerException             在android.support.v7.widget.RecyclerView.onMeasure 在设置适配器后的主要活动中。

我不确定我做错了什么。我试图阅读其他问题，但解决方案不起作用。如果有人可以指导我正确的方向作为我在Android中编程的新手，将不胜感激。感谢。

此处还有完整的错误

log:06-26 12:41:50.014  31158-31158/alexgwartney.treehouseblogreader E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: alexgwartney.treehouseblogreader, PID: 31158
    java.lang.NullPointerException
            at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:1764)
            at android.view.View.measure(View.java:16849)
            at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:824)
            at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:500)
            at android.view.View.measure(View.java:16849)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5378)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:340)
            at android.support.v7.internal.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:124)
            at android.view.View.measure(View.java:16849)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5378)
            at android.support.v7.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:444)
            at android.view.View.measure(View.java:16849)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5378)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:340)
            at android.view.View.measure(View.java:16849)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5378)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1621)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:742)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:607)
            at android.view.View.measure(View.java:16849)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5378)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:340)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2368)
            at android.view.View.measure(View.java:16849)
            at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2271)
            at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1334)
            at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1532)
            at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1211)
            at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6282)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:788)
            at android.view.Choreographer.doCallbacks(Choreographer.java:591)
            at android.view.Choreographer.doFrame(Choreographer.java:560)
            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:774)
            at android.os.Handler.handleCallback(Handler.java:808)
            at android.os.Handler.dispatchMessage(Handler.java:103)
            at android.os.Looper.loop(Looper.java:193)
            at android.app.ActivityThread.main(ActivityThread.java:5323)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:825)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:641)
            at dalvik.system.NativeStart.main(Native Method)


public class MainActivity extends ActionBarActivity {
public String url = "http://blog.teamtreehouse.com/api/get_recent_summary/?count=20";
public static final String TAG = MainActivity.class.getSimpleName();
private RecyclerView mRecyclerView;
private RecyclerView.Adapter mAdapter;

content[] mDataset;

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


    mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);

    if(isNetworkAvailable()) {
        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder()
                .url(url)
                .build();

        Call call = client.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Request request, IOException e) {

            }

            @Override
            public void onResponse(Response response) throws IOException {
                try {
                    String jsonData = response.body().string();
                    Log.v(TAG, jsonData);
                    if (response.isSuccessful()) {
                        getCurrentDetails(jsonData);
                        mAdapter = new MyAdapter(mDataset);
                        mRecyclerView.setAdapter(mAdapter);

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

                        mRecyclerView.setHasFixedSize(true);
                    }
                } catch (IOException e) {
                    Log.e(TAG, "Exception caught: ", e);
                } catch (JSONException e) {
                    Log.e(TAG, "Exception caught: ", e);
                }
            }
        });
    }


}


private content[] getCurrentDetails(String jsonData) throws JSONException {
    JSONObject forecast = new JSONObject(jsonData);

    JSONArray data = forecast.getJSONArray("posts");

     mDataset = new content[data.length()];

    for (int i = 0; i < data.length(); i++) {

        JSONObject jsonDay = data.getJSONObject(i);
        content day = new content();

        day.setId(jsonDay.getInt("id"));
        day.setUrl(jsonDay.getString("url"));
        day.setTitle(jsonDay.getString("title"));
        day.setDate(jsonDay.getString("date"));
        day.setAuthor(jsonDay.getString("author"));
        day.setThumbnail(jsonDay.getString("thumbnail"));
        mDataset[i] = day;
    }


    return mDataset;

}


// This will check if there is a net work conection
private boolean isNetworkAvailable() {
    ConnectivityManager manager = (ConnectivityManager)
            getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = manager.getActiveNetworkInfo();
    boolean isAvailable = false;
    if (networkInfo != null && networkInfo.isConnected()) {
        isAvailable = true;
    }
    return isAvailable;
}

} 

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.HourViewHolder> {
public  content[] mDataset;


public MyAdapter(content[] data) {
    mDataset = data;

}




//  the lay out is not the correct lay out but its just there for a example.
@Override
public HourViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.test, parent, false);
    HourViewHolder viewHolder = new HourViewHolder(view);
    return viewHolder;
}

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

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

public class HourViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

    public TextView mId;
    public TextView mUrl;
    public TextView mTitle;
    public TextView mDate;
    public TextView mAuthor;
    public TextView mThumbnail;

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

        mId = (TextView) itemView.findViewById(R.id.blogid);
        mUrl= (TextView) itemView.findViewById(R.id.url);
        mTitle = (TextView) itemView.findViewById(R.id.title);
        mDate = (TextView) itemView.findViewById(R.id.date);
        mAuthor = (TextView) itemView.findViewById(R.id.author);
        mThumbnail= (TextView) itemView.findViewById(R.id.thumbnail);
    }

    public void bindHour(content hour) {
        mId.setText(hour.getId());
        mUrl.setText(hour.getUrl());
        mTitle.setText(hour.getTitle());
        mDate.setText(hour.getDate());
        mAuthor.setText(hour.getAuthor());
        mThumbnail.setText(hour.getThumbnail());
    }

    @Override
    public void onClick(View view) {

    }
}

}

3 个答案:

答案 0 :(得分：0)

在设置适配器之前设置layoutManager。如果有效，请告诉我。

答案 1 :(得分：0)

您应该在您的oncreate中启动recyclerview，而不是在回调中。

  protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    //init recyclerview
            mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);
            RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(MainActivity.this);
            mRecyclerView.setLayoutManager(layoutManager);
            mRecyclerView.setHasFixedSize(true);
            mAdapter = new MyAdapter(new MyAdatpter());
            mRecyclerView.setAdapter(mAdapter);

            if (isNetworkAvailable()) {
                OkHttpClient client = new OkHttpClient();
                Request request = new Request.Builder()
                        .url(url)
                        .build();

                Call call = client.newCall(request);
                call.enqueue(new Callback() {
                    @Override
                    public void onFailure(Request request, IOException e) {

                    }

                    @Override
                    public void onResponse(Response response) throws IOException {
                        try {
                            String jsonData = response.body().string();
                            Log.v(TAG, jsonData);
                            if (response.isSuccessful()) {
// only switch the recyclerview adapter
// or extend your adapter with a clear() and add(List<>) function to avoid creating always a new adapter
// This code must run on ui thread
                                mRecyclerView.setAdapter(new MyAdapter(getCurrentDetails(jsonData)));
                            }
                        } catch (IOException e) {
                            Log.e(TAG, "Exception caught: ", e);
                        } catch (JSONException e) {
                            Log.e(TAG, "Exception caught: ", e);
                        }
                    }
                });
            }
        }

添加了评论。

答案 2 :(得分：0)

所以我发现我需要在主ui线程上运行适配器。

public class MainActivity extends ActionBarActivity {

    public String url = "http://blog.teamtreehouse.com/api/get_recent_summary/?count=20";
    public static final String TAG = MainActivity.class.getSimpleName();
    private RecyclerView mRecyclerView;
    private RecyclerView.Adapter mAdapter;

    content[] mDataset;

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

        mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        mRecyclerView.setLayoutManager(layoutManager);


        if(isNetworkAvailable()) {
            OkHttpClient client = new OkHttpClient();
            Request request = new Request.Builder()
                    .url(url)
                    .build();

            Call call = client.newCall(request);
            call.enqueue(new Callback() {
                @Override
                public void onFailure(Request request, IOException e) {

                }

                @Override
                public void onResponse(Response response) throws IOException {
                    try {
                        String jsonData = response.body().string();
                        Log.v(TAG, jsonData);
                        if (response.isSuccessful()) {
                            getCurrentDetails(jsonData);

                            runOnUiThread(new Runnable() {
                                @Override
                                public void run() {
                                    mAdapter = new MyAdapter(mDataset);
                                    mRecyclerView.setAdapter(mAdapter);
                                }
                            });



                        }
                    } catch (IOException e) {
                        Log.e(TAG, "Exception caught: ", e);
                    } catch (JSONException e) {
                        Log.e(TAG, "Exception caught: ", e);
                    }
                }
            });
        }
    }

    private content[] getCurrentDetails(String jsonData) throws JSONException {
        JSONObject forecast = new JSONObject(jsonData);
        JSONArray data = forecast.getJSONArray("posts");
        mDataset = new content[data.length()];

        for (int i = 0; i < data.length(); i++) {

            JSONObject jsonDay = data.getJSONObject(i);
            content day = new content();

            day.setId(jsonDay.getInt("id"));
            day.setUrl(jsonDay.getString("url"));
            day.setTitle(jsonDay.getString("title"));
            day.setDate(jsonDay.getString("date"));
            day.setAuthor(jsonDay.getString("author"));
            day.setThumbnail(jsonDay.getString("thumbnail"));
            mDataset[i] = day;
        }
        return mDataset;
    }

    // This will check if there is a net work conection
    private boolean isNetworkAvailable() {
        ConnectivityManager manager = (ConnectivityManager)
                getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = manager.getActiveNetworkInfo();
        boolean isAvailable = false;
        if (networkInfo != null && networkInfo.isConnected()) {
            isAvailable = true;
        }
        return isAvailable;
    }
}
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