出现未知错误

Question

在我的应用程序中，有些活动我曾经从解析服务器调用数据，但在打开任何活动后突然发生应用程序崩溃，并在重新启动应用程序后打开了

Four.java

@ParseClassName("Four")
public class Four extends ParseObject{
    public Four(){    
    }

    public String getFourc(){
        return getString("fourc");
    }

    public void setFourc(String fourc){
        put("fourc", fourc);
    }
}

四个适配器

  public class FourAdapter extends ArrayAdapter<Four> {
    private Context mContext;
    private List<Four> mFours;

    public FourAdapter(Context context, List<Four> objects) {
        super(context, R.layout.four_row_item, objects);
        this.mContext = context;
        this.mFours = objects;
    }


    public View getView(int position, View convertView, ViewGroup parent){
        if(convertView == null){
            LayoutInflater mLayoutInflater = LayoutInflater.from(mContext);
            convertView = mLayoutInflater.inflate(R.layout.four_row_item, null);
        }

        Four four = mFours.get(position);

        TextView descriptionView = (TextView) convertView.findViewById(R.id.four_fourc);

        descriptionView.setText(four.getFourc());

        return convertView;
    }
}

FourActivity

public class FourActivity extends AppCompatActivity {
    private ListView mListView;
    private FourAdapter mAdapter;
    ProgressBar progressBar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_four);
        //noinspection ConstantConditions

        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        getSupportActionBar().setIcon(R.drawable.gpsicon);

        mAdapter = new FourAdapter(this, new ArrayList<Four>());
        progressBar = (ProgressBar) findViewById(R.id.loading);
        mListView = (ListView) findViewById(R.id.four_list);

        mListView.setAdapter(mAdapter);

        ParseQuery<Four> query = ParseQuery.getQuery(Four.class);

        query.findInBackground(new FindCallback<Four>() {
            public void done(List<Four> fours, ParseException error) {
                if (fours != null) {
                    mAdapter.clear();
                    progressBar.setVisibility(View.GONE);
                    for (int i = 0; i < fours.size(); i++) {
                        mAdapter.add(fours.get(i));
                    }
                }
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_four, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_notice) {
            Intent i = new Intent(this, FonActivity.class);
            startActivity(i);
            return true;
        }

        if (id == R.id.home) {
            this.finish();
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

LogCat错误

09-23 23:07:11.776    2400-2400/com.school.gurunanakpublicschool E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.ClassCastException: com.parse.ParseObject cannot be cast to com.school.gurunanakpublicschool.Four
        at com.school.gurunanakpublicschool.FourAdapter.getView(FourAdapter.java:29)
        at android.widget.AbsListView.obtainView(AbsListView.java:2177)
        at android.widget.ListView.measureHeightOfChildren(ListView.java:1247)
        at android.widget.ListView.onMeasure(ListView.java:1159)
        at android.view.View.measure(View.java:15848)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5012)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
        at android.view.View.measure(View.java:15848)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5012)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at android.support.v7.internal.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:124)
        at android.view.View.measure(View.java:15848)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5012)
        at android.support.v7.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:444)
        at android.view.View.measure(View.java:15848)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5012)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at android.view.View.measure(View.java:15848)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5012)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
        at android.view.View.measure(View.java:15848)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5012)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2189)
        at android.view.View.measure(View.java:15848)
        at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1905)
        at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1104)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1284)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1004)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5481)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
        at android.view.Choreographer.doCallbacks(Choreographer.java:562)
        at android.view.Choreographer.doFrame(Choreographer.java:532)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
        at android.os.Handler.handleCallback(Handler.java:730)
        at android.os.Handler.dispatchMessage(Handler.java:92)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:5103)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:525)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
        at dalvik.system.NativeStart.main(Native Method)

App在任何活动中随机崩溃，还有更多此类活动请帮帮我。