Как загрузить контент на основе первого счетчика?

Question

Я не уверен, почему это не работает. Я получаю ошибку журнала Cat с указанием FATAL EXCEPTION: main java.lang.NullPointer Exception at com.example.bertin.HotelLocation.onItemSelected. Вот код. По-видимому, мне кажется правильным, что я думаю, что я ошибаюсь.

package com.example.bertin; 

import android.app.Activity; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.AdapterView.OnItemSelectedListener; 
import android.widget.ArrayAdapter; 
import android.widget.Spinner; 

public class HotelLocation extends Activity implements OnItemSelectedListener { 

    Spinner countrySpinner, citySpinner; 
    private ArrayAdapter<String> countryAdapter; 
    private ArrayAdapter<String> cityAdapter; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_hotel_location); 

     Spinner countrySpinner = (Spinner) findViewById(R.id.spinnerHotelCountry); 
     Spinner citySpinner = (Spinner) findViewById(R.id.spinnerHotelCity); 

     // Create an ArrayAdapter using the string array and a default spinner 
     // layout 
     ArrayAdapter<CharSequence> countryAdapter = ArrayAdapter 
       .createFromResource(this, R.array.countries, 
         android.R.layout.simple_spinner_item); 
     ArrayAdapter<CharSequence> cityAdapter = ArrayAdapter 
       .createFromResource(this, R.array.australia, 
         android.R.layout.simple_spinner_item); 

     // Specify the layout to use when the list of choices appears 
     countryAdapter 
       .setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); 
     cityAdapter 
       .setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); 

     // Apply the adapter to the spinner 
     countrySpinner.setAdapter(countryAdapter); 
     citySpinner.setAdapter(cityAdapter); 

     countrySpinner.setOnItemSelectedListener(this); 
     // citySpinner.setOnItemSelectedListener(this); 

    } 

    @Override 
    public void onItemSelected(AdapterView<?> parent, View view, int position, 
      long id) { 
     String[] citySpinnerArray = null; 
     String selected = parent.getItemAtPosition(position).toString(); 
     if (selected.equals("Australia")) { 

      citySpinnerArray = getResources().getStringArray(R.array.australia); 


     } 
     citySpinner.setAdapter(new ArrayAdapter(this, 
       android.R.layout.simple_spinner_item, citySpinnerArray)); 

    } 

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

    @Override 
    public void onNothingSelected(AdapterView<?> arg0) { 
     // TODO Auto-generated method stub 

    } 

} 

StackTrace:

09-10 03:42:02.484: E/AndroidRuntime(2160): FATAL EXCEPTION: main 

09-10 03:42:02.484: E/AndroidRuntime(2160): java.lang.NullPointerException 

09-10 03:42:02.484: E/AndroidRuntime(2160):  at com.example.bertin.HotelLocation.onItemSelected(HotelLocation.java:97) 

09-10 03:42:02.484: E/AndroidRuntime(2160):  at android.widget.AdapterView.fireOnSelected(AdapterView.java:892) 

09-10 03:42:02.484: E/AndroidRuntime(2160):  at android.widget.AdapterView.access$200(AdapterView.java:49) 

09-10 03:42:02.484: E/AndroidRuntime(2160):  at android.widget.AdapterView$SelectionNotifier.run(AdapterView.java:860) 

09-10 03:42:02.484: E/AndroidRuntime(2160):  at android.os.Handler.handleCallback(Handler.java:730) 

09-10 03:42:02.484: E/AndroidRuntime(2160):  at android.os.Handler.dispatchMessage(Handler.java:92) 

09-10 03:42:02.484: E/AndroidRuntime(2160):  at android.os.Looper.loop(Looper.java:137) 

09-10 03:42:02.484: E/AndroidRuntime(2160):  at android.app.ActivityThread.main(ActivityThread.java:5103) 

09-10 03:42:02.484: E/AndroidRuntime(2160):  at java.lang.reflect.Method.invokeNative(Native Method) 

09-10 03:42:02.484: E/AndroidRuntime(2160):  at java.lang.reflect.Method.invoke(Method.java:525) 

09-10 03:42:02.484: E/AndroidRuntime(2160):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737) 

09-10 03:42:02.484: E/AndroidRuntime(2160):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 

09-10 03:42:02.484: E/AndroidRuntime(2160):  at dalvik.system.NativeStart.main(Native Method) 

Answer 1

// Just replace this two line your code working perfectly. 
Spinner countrySpinner = (Spinner) findViewById(R.id.spinnerHotelCountry); 
Spinner citySpinner = (Spinner) findViewById(R.id.spinnerHotelCity); 
        to 
countrySpinner = (Spinner) findViewById(R.id.spinnerHotelCountry); 
citySpinner = (Spinner) findViewById(R.id.spinnerHotelCity); 

Answer 2

Попробуйте этот способ

@Override 
    public void onItemSelected(AdapterView<?> parent, View view, int position, 
      long id) { 

     String selected = parent.getItemAtPosition(position).toString(); 
     if (selected.equals("Australia")) { 


     citySpinner.setAdapterArrayAdapter 
       .createFromResource(this, R.array.australia, 
         android.R.layout.simple_spinner_item)); 


     } 

    } 

Answer 3

Попробуйте это:

@Override 
    public void onItemSelected(AdapterView<?> parent, View view, int position, 
      long id) { 
     String[] citySpinnerArray = null; 
     String selected = parent.getItemAtPosition(position).toString(); 
     if (selected.equals("Australia")) { 

      citySpinnerArray = getResources().getStringArray(R.array.australia); 

      citySpinner.setAdapter(new ArrayAdapter(this, 
       android.R.layout.simple_spinner_item, citySpinnerArray)); 
     } 
}