解析运行时错误：说我有空引用：Android Studio

Question

我正在尝试从狗品种网站解析数据，但我在此活动中遇到运行时错误，这是我的第一个活动。有人知道我做错了什么或者能说出我的错误吗？

谢谢

Unable to start activity   ComponentInfo{com.example.shannon.popular/com.example.shannon.popular.DogsActivity}: java.lang.NullPointerException: Attempt to invoke virtual method      '  com.example.shannon.popular.Breed$Name      com.example.shannon.popular.Breed.getName()' on a null object reference
  at    android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
 at android.app.ActivityThread.access$800(ActivityThread.java:144)
  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
  at android.os.Handler.dispatchMessage(Handler.java:102)

Dog Activity.class

public class DogsActivity extends Activity {


private Breed breed;
private Dogs dogs;
private DogAdapter dogAdapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    dogs = new Dogs();
    Intent intent = getIntent();
    breed = (Breed) intent.getSerializableExtra("breed");
    Breed.Name breedName = breed.getName();
    String url = breed.getURL();


    //todo remove hard code page number
    if (breedName == Breed.Name.MOST_POPULAR) {
        new RetrieveDogsTask().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, url);
        new RetrieveDogsTask().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, url + "list_1_2.html");
        new RetrieveDogsTask().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, url + "list_1_3.html");
    } else if (breedName == Breed.Name.HERDING_BREED) {
        new RetrieveDogsTask().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, url);
        new RetrieveDogsTask().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, url + "list_11_2.html");
        new RetrieveDogsTask().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, url + "list_11_3.html");
    } else if (breedName == Breed.Name.WORKING_BREED) {
        //todo remove hard code urls
        new RetrieveDogsTask().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR,
                "http://www.dogbreedslist.info/all-dog-breeds/Boxer.html#.Vh0cnRNViko");
        new RetrieveDogsTask().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR,
                "http://www.dogbreedslist.info/all-dog-breeds/Chinook-dog.html#.Vh0cvBNViko");
        new RetrieveDogsTask().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR,
                "http://www.dogbreedslist.info/all-dog-breeds/Rottweiler.html#.Vh0c0xNViko");
        new RetrieveDogsTask().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR,
                "http://www.dogbreedslist.info/all-dog-breeds/Kuvasz.html#.Vh0c6BNViko");
        new RetrieveDogsTask().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR,
                "http://www.dogbreedslist.info/all-dog-breeds/Argentine-Dogo.html#.Vh0dARNViko");
    } else {
        new RetrieveDogsTask().execute(url);
    }
    setContentView(R.layout.activity_dogs);
    GridView gridView = (GridView) findViewById(R.id.dogsGridView);

    Display display = getWindowManager().getDefaultDisplay();
    Point size = new Point();
    display.getSize(size);
    int width = size.x;
    int height = size.y;
    int thumbnail_width;
    int thumbnail_height;
    if (breedName == Breed.Name.MOST_POPULAR) {
        thumbnail_width = (int) getResources().getDimension(R.dimen.first_team_thumbnail_width);
        thumbnail_height = (int) getResources().getDimension(R.dimen.first_team_thumbnail_height);
        gridView.setColumnWidth(thumbnail_width);
        int n = width / thumbnail_width * height / thumbnail_height;
       dogs.fillEmptyData(n);
    } else if (breedName ==Breed.Name.WORKING_BREED) {
        gridView.setColumnWidth((int) getResources().getDimension(R.dimen.coach_thumbnail_width));
    } else {
        thumbnail_width = (int) getResources().getDimension(R.dimen.reserve_thumbnail_box_width);
        thumbnail_height = (int) getResources().getDimension(R.dimen.reserve_thumbnail_height);
        gridView.setColumnWidth(thumbnail_width);
        int n = width / thumbnail_width * height / thumbnail_height;
        dogs.fillEmptyData(n);
    }
    gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {

            Dog dog = dogs.get(position);
            Toast.makeText(getApplicationContext(), dog.getName(),
                    Toast.LENGTH_SHORT).show();
            Intent dogProfileIntent = new Intent(DogsActivity.this,
                    DogProfileActivity.class);
            Bundle dogBundle = new Bundle();
            dogBundle.putSerializable("dog", dog);
            dogProfileIntent.putExtras(dogBundle);
            startActivity(dogProfileIntent);
        }
    });
    dogAdapter = new DogAdapter
            (DogsActivity.this, R.layout.activity_dogs, dogs, breedName);
    gridView.setAdapter(dogAdapter);
    setTitle(breed.getNameString(this));


}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.breeds, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.website) {
        Intent intent = new Intent(DogsActivity.this,
                WebViewActivity.class);
        intent.putExtra("url", breed.getURL());
        intent.putExtra("title", breed.getNameString(this));
        startActivity(intent);
        return true;
    }
    return super.onOptionsItemSelected(item);
}

private class RetrieveDogsTask extends AsyncTask<String, Void, Void> {
    @Override
    protected Void doInBackground(String... urls) {
        for (String url : urls) {
            Parser parser = new Parser(url, DogsActivity.this);
            Breed.Name breedName = breed.getName();
            if (breedName == Breed.Name.WORKING_BREED) {
                dogs.add(parser.parseProfile(new Dog(url, breedName)));
            } else {
                dogs.addAll(parser.parseDogsPage(breedName, DogsActivity.this));
            }
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);
        dogAdapter.notifyDataSetChanged();
    }
}

这是我的数据：

    package com.example.shannon.popular;

import java.io.Serializable;
import java.util.ArrayList;


 class Dog implements Serializable {
   private String name;
   private String origin;
   private String lifeSpan;
   private String sizeType;
   private String otherNames;
   private ArrayList<Detail> details;
  private String thumbnailURL;
private String mainImageURL;
private String url;
private String articleText = "";
private Breed.Name breed;
//Like a lock in multi threading
private boolean basicDataReady = false;
private boolean detailDataReady = false;

Dog(String name, String sizeType, String thumbnailURL, String url, Breed.Name breed) {
    this.name = name;
    this.sizeType = sizeType;
    this.thumbnailURL = thumbnailURL;
    this.url = url;
    this.breed = breed;
    basicDataReady = true;
}

Dog(String name, String origin, String lifeSpan, String url, String thumbnailURL, Breed.Name breed) {
    this.name = name;
    this.origin = origin;
    this.lifeSpan = lifeSpan;
    this.url = url;
    this.thumbnailURL = thumbnailURL;
    this.breed = breed;
    basicDataReady = true;
}

Dog(String name, String url, String thumbnailURL, Breed.Name breed) {
    this.name = name;
    this.url = url;
    this.thumbnailURL = thumbnailURL;
    this.breed = breed;
    basicDataReady = true;
}

Dog(String url, Breed.Name breed) {
    this.url = url;
    this.breed = breed;
}

Dog() {

}

public String getArticleText() {
    return articleText;
}

public void setArticleText(String articleText) {
    this.articleText = articleText;
}

public String getOrigin() {
    return origin;
}

public String getLifeSpan() {
    return lifeSpan;
}

public String getSizeType() {
    return sizeType;
}

public boolean isBasicDataReady() {
    return basicDataReady;
}

public void setBasicDataReady(boolean basicDataReady) {
    this.basicDataReady = basicDataReady;
}

public boolean isDetailDataReady() {
    return detailDataReady;
}

public void setDetailDataReady(boolean detailDataReady) {
    this.detailDataReady = detailDataReady;
}

public Breed.Name getBreed() {
    return breed;
}

public void setBreed(Breed.Name breed) {
    this.breed = breed;
}

public String getMainImageURL() {
    return mainImageURL;
}

public void setMainImageURL(String mainImageURL) {
    this.mainImageURL = mainImageURL;
}

public ArrayList<Detail> getDetails() {
    return details;
}

public void setDetails(ArrayList<Detail> details) {
    this.details = details;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getOtherNames() {
    return otherNames;
}

public void setOtherNames(String otherNames) {
    this.otherNames = otherNames;
}

public String getThumbnailURL() {
    return thumbnailURL;
}

public void setThumbnailURL(String thumbnailURL) {
    this.thumbnailURL = thumbnailURL;
}

public String getUrl() {
    return url;
}


static class Detail implements Serializable {
    private final String key;
    private final String value;

    public Detail(String key, String value) {
        this.key = key;
        this.value = value;
    }

    public String getValue() {
        return value;
    }

    public String getKey() {
        return key;
    }
}

}