我在MainActivity中通过片段制作了3个标签，我想在其中一个片段中使用Yahoo weather API来显示简单的天气预报。当我运行代码时，应用程序已停止并获得 NullPointerException 。
07-30 16:27:34.719 11633-11633/com.example.frank.prototype3 E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.NullPointerException
at com.example.frank.prototype3.fragments.ActivityFragment.onCreate(ActivityFragment.java:73)
at android.support.v4.app.Fragment.performCreate(Fragment.java:1766)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:917)
at android.support.v4.app.FragmentManagerImpl.performPendingDeferredStart(FragmentManager.java:846)
at android.support.v4.app.Fragment.setUserVisibleHint(Fragment.java:860)
at android.support.v4.app.FragmentStatePagerAdapter.setPrimaryItem(FragmentStatePagerAdapter.java:152)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1103)
at android.support.v4.view.ViewPager.populate(ViewPager.java:951)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1473)
at android.view.View.measure(View.java:15483)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:833)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
at android.view.View.measure(View.java:15483)
at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:868)
at android.view.View.measure(View.java:15483)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4843)
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:15483)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4843)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1390)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:681)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
at android.view.View.measure(View.java:15483)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4843)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
at android.view.View.measure(View.java:15483)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4843)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1390)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:681)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
at android.view.View.measure(View.java:15483)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4843)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2192)
at android.view.View.measure(View.java:15483)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1891)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1100)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1286)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4293)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
at android.view.Choreographer.doCallbacks(Choreographer.java:555)
at android.view.Choreographer.doFrame(Choreographer.java:525)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)
at android.os.Handler.handleCallback(Handler.java:615)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4866)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
这是我的MainActivity
public class MainActivity extends ActionBarActivity {
private Toolbar toolbar;
private ViewPager mPager;
private SlidingTabLayout mTabs;
public static final int ACTIVITY = 0;
public static final int GROUP = 1;
public static final int RECORD = 2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
toolbar = (Toolbar) findViewById(R.id.app_bar);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayShowHomeEnabled(true);
NavigationDrawerFragment drawerFragment = (NavigationDrawerFragment)getFragmentManager().findFragmentById(R.id.fragment_navigation_drawer);
drawerFragment.setUp(R.id.fragment_navigation_drawer, (DrawerLayout) findViewById(R.id.drawer_layout), toolbar);
mPager = (ViewPager)findViewById(R.id.pager);
mPager.setAdapter(new MyPagerAdapter(getSupportFragmentManager()));
mTabs = (SlidingTabLayout)findViewById(R.id.tabs);
mTabs.setDistributeEvenly(true);
mTabs.setCustomTabView(R.layout.custom_tab_view, R.id.tabText);
mTabs.setBackgroundColor(getResources().getColor(R.color.colorPrimary));
mTabs.setSelectedIndicatorColors(getResources().getColor(R.color.colorAccent));
mTabs.setViewPager(mPager);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, 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();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
if(id == R.id.navigate){
startActivity(new Intent(this, SubActivity.class));
}
return super.onOptionsItemSelected(item);
}
class MyPagerAdapter extends FragmentStatePagerAdapter {
int icons[] = {R.mipmap.ic_action_record, R.mipmap.ic_action_bike, R.mipmap.ic_action_group};
String[] tabText = getResources().getStringArray(R.array.tabs);
public MyPagerAdapter(FragmentManager fm) {
super(fm);
tabText = getResources().getStringArray(R.array.tabs);
}
@Override
public Fragment getItem(int num) {
Fragment fragment = null;
switch(num){
case RECORD:
fragment = RecordFragment.newInstance("","");
break;
case ACTIVITY:
fragment = ActivityFragment.newInstance("","");
break;
case GROUP:
fragment = GroupFragment.newInstance("","");
}
return fragment;
}
@Override
public CharSequence getPageTitle(int position) {
Drawable drawable = getResources().getDrawable(icons[position]);
drawable.setBounds(0,0,36,36);
ImageSpan imageSpan = new ImageSpan(drawable);
SpannableString spannableString = new SpannableString(" ");
spannableString.setSpan(imageSpan, 0, spannableString.length(), Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
return spannableString;
}
@Override
public int getCount() {
return 3;
}
}
public static class MyFragment extends Fragment {
private TextView textView;
public static MyFragment getInstance(int position){
MyFragment myFragment = new MyFragment();
Bundle args = new Bundle();
args.putInt("position",position);
myFragment.setArguments(args);
return myFragment;
}
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View layout = inflater.inflate(R.layout.fragment_my, container, false);
textView = (TextView) layout.findViewById(R.id.position);
Bundle bundle = getArguments();
if(bundle !=null){
textView.setText("The page selected is" + bundle.getInt("position"));
}
return layout;
}
}
}
这是我想要参与api，ActivityFragment
的片段类之一public class ActivityFragment extends Fragment implements WeatherServiceCallBack{
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
private ImageView weatherIconImageView;
private TextView temperatureTextView;
private TextView conditionTextView;
private TextView locationTextView;
private WeatherService service;
private ProgressDialog dialog;
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @param param2 Parameter 2.
* @return A new instance of fragment ActivityFragment.
*/
// TODO: Rename and change types and number of parameters
public static ActivityFragment newInstance(String param1, String param2) {
ActivityFragment fragment = new ActivityFragment();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
public ActivityFragment() {
// Required empty public constructor
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
weatherIconImageView = (ImageView) getView().findViewById(R.id.weatherIconImageView);
temperatureTextView = (TextView) getView().findViewById(R.id.temperatureTextView);
conditionTextView = (TextView) getView().findViewById(R.id.conditionTextView);
locationTextView = (TextView) getView().findViewById(R.id.locationTextView);
service = new WeatherService(this, getActivity());
dialog = new ProgressDialog(getActivity());
dialog.setMessage("Loading...");
dialog.show();
service.refreshWeather("Austin, TX");
}
@Override
public void serviceSuccess(Channel channel) {
dialog.hide();
Item item = channel.getItem();
int resourceId = getResources().getIdentifier("drawable/icon_" + item.getCondition().getCode(), null, getActivity().getPackageName());
@SuppressWarnings("deprecation")
Drawable weatherIconDrawble = getResources().getDrawable(resourceId);
weatherIconImageView.setImageDrawable(weatherIconDrawble);
temperatureTextView.setText(item.getCondition().getTemperature() + "\u00B0" + channel.getUnits().getTemperature());
conditionTextView.setText(item.getCondition().getDescription());
locationTextView.setText(channel.getLocation());
}
@Override
public void serviceFailure(Exception exception) {
dialog.hide();
Toast.makeText(getActivity(), exception.getMessage(), Toast.LENGTH_LONG).show();
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_group, container, false);
}
}
我是Android的初学者，现在非常困惑。我需要你们的帮助，非常感谢！