我试图在模拟器中运行应用程序,但每次崩溃时 我得到了由以下原因引起的错误:
[" Java.lang.nullPointerException at(android.support.v4.app.backstackrecord.doAddOp(Backstackrecord.java:394)"]
我尝试了所有我知道但我还是坚持了! 我想我错过了一些代码,但我不知道它是什么!
以下是所有logcat Full logcat的链接
这是MainActivity.java
类:
public class MainActivity extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null)
{
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new ForecastFragment()
.Commit());
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.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();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public ForecastFragment Commit() {
return null;
}
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
String forecastJsonStr = null;
}
这是ForecastFragment.java
类:
public class ForecastFragment extends Fragment {
public ForecastFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setHasOptionsMenu(true);
}
public void onCreateOptionMenu(Menu menu, MenuInflater inflater) {
inflater.inflate(R.menu.forecastfragment, menu);
}
public boolean onOptionItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_refresh) {
FetchWeatherTask weatherTask = new FetchWeatherTask();
weatherTask.execute("94043");
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
String[] data = {
"Today - Sunny - 88/63",
"Tomorrow - foggy - 70/46",
"weds - Cloudy - 72/63",
"Thurs - Rainy - 64/51",
"Fri - Foggy - 70/46",
"Sat - Sunny - 76/68"
};
List<String> weekForecast = new ArrayList<String>(
Arrays.asList(data));
ArrayAdapter<String> mForecastAdapter =
new ArrayAdapter<String>(
getActivity(),
R.layout.list_item_forecast,
R.id.list_item_forecast_textview,
weekForecast );
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
ListView listView = (ListView) rootView.findViewById(R.id.listview_forecast);
listView.setAdapter(mForecastAdapter);
return rootView;
}
public ForecastFragment Commit() {
return null;
}
public class FetchWeatherTask extends AsyncTask<String, Void, Void> {
private final String LOG_TAG = FetchWeatherTask.class.getSimpleName();
private String getReadableDataString(long time) {
Date date = new Date(time * 1000);
SimpleDateFormat format = new SimpleDateFormat("E, MMM d");
return format.format(date).toString();
}
protected String[] doInBackGround(String... params) {
if (params.length == 0) {
return null;
}
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
String forecastJsonStr = null;
String format = "json";
String units = "metric";
int numDays = 7;
try {
final String FORECAST_BASE_URL =
"http://api.openweathermap.org/data/2.5/forecast/daily?";
final String QUERY_PARAM = "q";
final String FORMAT_param = "MODE";
final String UNITS_param = "UNITS";
final String DAYS_param = "CNT";
Uri builtUri = Uri.parse(FORECAST_BASE_URL).buildUpon()
.appendQueryParameter(QUERY_PARAM, params[0])
.appendQueryParameter(FORMAT_param, format)
.appendQueryParameter(UNITS_param, format)
.appendQueryParameter(DAYS_param, Integer.toString(numDays))
.build();
URL url = new URL(builtUri.toString());
Log.v(LOG_TAG, "Built Uri " + builtUri.toString());
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.connect();
InputStream inputStream = urlConnection.getInputStream();
StringBuffer buffer = new StringBuffer();
if (inputStream == null) {
return null;
}
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null) {
buffer.append(line + "\n");
}
if (buffer.length() == 0) {
return null;
}
forecastJsonStr = buffer.toString();
Log.v(LOG_TAG, "Forecast JSON String: " + forecastJsonStr);
} catch (IOException e) {
Log.e(LOG_TAG, "Error", e);
return null;
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
if (reader != null) {
try {
reader.close();
} catch (final IOException e) {
Log.e(LOG_TAG, "Error closing stream", e);
}
}
}
return getWeatherDataFromJson(forecastJsonStr, numDays);
}
@Override
protected Void doInBackground(String... params) {
return null;
}
}
public String[] getWeatherDataFromJson(String forecastJsonStr, int numDays) {
return new String[0];
}
}
谢谢!
答案 0 :(得分:1)
您的NullPointerException位于onCreate的MainActivity的第20行。你似乎在那里放错了一些括号:
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new ForecastFragment()
.Commit());
对片段进行Commit()
。它必须是
getSupportFragmentManager()
.beginTransaction()
.add(R.id.container, new ForecastFragment())
.commit();
如果这不能解决,您可以调试对象并检查哪一个为空。