Question

我试图使用列表视图，所以显示我的日期，但我得到例外。当我运行我的应用程序是抛出运行时异常。请告诉我我必须做什么来摆脱这个execption：这是我的例外

08-06 12:17:09.278: E/AndroidRuntime(3709): FATAL EXCEPTION: main
08-06 12:17:09.278: E/AndroidRuntime(3709): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.gridtestproject/com.example.gridtestproject.TestActivity}: java.lang.NullPointerException
08-06 12:17:09.278: E/AndroidRuntime(3709):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
08-06 12:17:09.278: E/AndroidRuntime(3709):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
08-06 12:17:09.278: E/AndroidRuntime(3709):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
08-06 12:17:09.278: E/AndroidRuntime(3709):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
08-06 12:17:09.278: E/AndroidRuntime(3709):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-06 12:17:09.278: E/AndroidRuntime(3709):     at android.os.Looper.loop(Looper.java:137)
08-06 12:17:09.278: E/AndroidRuntime(3709):     at android.app.ActivityThread.main(ActivityThread.java:5041)
08-06 12:17:09.278: E/AndroidRuntime(3709):     at java.lang.reflect.Method.invokeNative(Native Method)
08-06 12:17:09.278: E/AndroidRuntime(3709):     at java.lang.reflect.Method.invoke(Method.java:511)
08-06 12:17:09.278: E/AndroidRuntime(3709):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
08-06 12:17:09.278: E/AndroidRuntime(3709):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
08-06 12:17:09.278: E/AndroidRuntime(3709):     at dalvik.system.NativeStart.main(Native Method)
08-06 12:17:09.278: E/AndroidRuntime(3709): Caused by: java.lang.NullPointerException
08-06 12:17:09.278: E/AndroidRuntime(3709):     at com.example.gridtestproject.TestActivity.onCreate(TestActivity.java:47)
08-06 12:17:09.278: E/AndroidRuntime(3709):     at android.app.Activity.performCreate(Activity.java:5104)
08-06 12:17:09.278: E/AndroidRuntime(3709):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
08-06 12:17:09.278: E/AndroidRuntime(3709):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
08-06 12:17:09.278: E/AndroidRuntime(3709):     ... 11 more

这是主类文件

public class TestActivity extends Activity {

    ListView onewayListView,ReturnListView;
    OneWayFlightResult onewaydata;
    ReturnFlightResult returndata;
    static final String FlightNumber = ""; // parent node
    static final String FlightCompanyName = "";
    static final String FlightTime = "";
    static final String FlightStop ="";
    static final String FlightCost ="";

/** Called when the activity is first created. */

@Override
protected void onCreate(Bundle savedInstanceState) {
    ArrayList<HashMap<String, String>> flightData = new ArrayList<HashMap<String, String>>();
    for (int i = 0; i < 12; i++) {
        // creating new HashMap
        HashMap<String, String> map = new HashMap<String, String>();

        // adding each child node to HashMap key => value
        map.put(FlightCompanyName, "SpiceJet");
        map.put(FlightNumber, "SG-123");
        map.put(FlightTime, "6:00 - 7:00");
        map.put(FlightStop, "1h 30m | Non Stop");
        map.put(FlightCost, "Rs 20,000");

        // adding HashList to ArrayList
        flightData.add(map);
    }


    onewayListView=(ListView)findViewById(R.id.lvDepartures);
    ReturnListView=(ListView)findViewById(R.id.lvArrivals);

    // Getting adapter by passing xml data ArrayList
    onewaydata=new OneWayFlightResult(this, flightData);        
    onewayListView.setAdapter(onewaydata);

   // returndata=new ReturnFlightResult(this, flightData);        
   // onewayListView.setAdapter(returndata);
    }
}

这是我的OneWayResult类代码

public class OneWayFlightResult extends BaseAdapter {

    private Activity activity;
    private ArrayList<HashMap<String, String>> data;
    private static LayoutInflater inflater=null;


    public OneWayFlightResult(Activity a, ArrayList<HashMap<String, String>> d) {
        activity = a;
        data=d;
        inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return data.size();
    }

    @Override
    public Object getItem(int position) {
        // TODO Auto-generated method stub
         return position;
    }

    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View vi=convertView;
        if(convertView==null)
            vi = inflater.inflate(R.layout.row, null);
        TextView flightTime = (TextView)vi.findViewById(R.id.flightTime); // title
        TextView flightCompanyName = (TextView)vi.findViewById(R.id.flightCompanyName); // title
        TextView flightNumber = (TextView)vi.findViewById(R.id.flightNumber); // title
        ImageView flightLogo = (ImageView)vi.findViewById(R.id.flightLogo);

        HashMap<String, String> flight = new HashMap<String, String>();
        flight = data.get(position);

        flightTime.setText(flight.get(TestActivity.FlightTime));
        flightCompanyName.setText(TestActivity.FlightCompanyName);
        flightNumber.setText(TestActivity.FlightNumber);
        return vi;
    }
}

Answer 1

您遗失setContentView。

  protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState); // missing
  setContentView(R.layout.mylayout); // missing
      ...// rest of the code
  }

您正在尝试初始化列表视图

      onewayListView=(ListView)findViewById(R.id.lvDepartures);

您尚未将内容设置为活动。因此，如果您尝试初始化，则会获得NullPointerException。

您可以findViewById将当前视图层次结构设置为活动。

在ListView Android中获取空指针异常

1 个答案: