Android Studio「嘗試在空對象引用上調用虛擬方法」

Question

我希望顯示1到3之間的數字，具體取決於您在兩個旋鈕中選擇的對象。一切都按照預期工作，直到我使用了以下代碼行，導致出錯。

int pos1 = spinnerW.getSelectedItemPosition(); 
int pos2 = spinnerS.getSelectedItemPosition(); 
Toast.makeText(getBaseContext(),ergebnis(pos1, pos2),Toast.LENGTH_LONG); 

是否有另一種方法來獲取所選對象的位置？ 在此先感謝。 全碼：

package com.example.peter.myapplication; 

import android.os.Bundle; 
import android.support.v7.app.AppCompatActivity; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.ArrayAdapter; 
import android.widget.Spinner; 
import android.widget.Toast; 
import android.widget.AdapterView.OnItemSelectedListener; 

public class MainActivity extends AppCompatActivity { 
    public static int ergebnis (int pos1, int pos2){ 
    int[][] array = new int[25][25]; 
    array[0][0] = 1; 
    array[0][1] = 1; 
    array[0][2] = 1; 
    array[0][3] = 2; 
    array[0][4] = 3; 
    array[1][0] = 1; 
    array[1][1] = 1; 
    array[1][2] = 1; 
    array[1][3] = 2; 
    array[1][4] = 3; 
    array[2][0] = 1; 
    array[2][1] = 1; 
    array[2][2] = 2; 
    array[2][3] = 2; 
    array[2][4] = 3; 
    array[3][0] = 1; 
    array[3][1] = 2; 
    array[3][2] = 2; 
    array[3][3] = 2; 
    array[3][4] = 3; 
    array[4][0] = 2; 
    array[4][1] = 2; 
    array[4][2] = 3; 
    array[4][3] = 3; 
    array[4][4] = 3; 
    return array[pos1][pos2]; 
} 

Spinner spinnerW; 
ArrayAdapter<CharSequence> adapterW; 
Spinner spinnerS; 
ArrayAdapter<CharSequence> adapterS; 

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

    spinnerW = (Spinner) findViewById(R.id.wahrscheinlichkeit); 
    adapterW = ArrayAdapter.createFromResource(this, R.array.wahrscheinlichkeit, android.R.layout.simple_spinner_item); 
    adapterW.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); 
    spinnerW.setAdapter(adapterW); 

    spinnerS.setOnItemSelectedListener(new OnItemSelectedListener() { 

     @Override 
     public void onItemSelected(AdapterView<?> parent, View view, int position, long id) { 
      Toast.makeText(getBaseContext(), parent.getItemAtPosition(position) + " ausgewählt", Toast.LENGTH_LONG).show(); 
     } 

     @Override 
     public void onNothingSelected(AdapterView<?> parent) { 

     } 
    }); 

    spinnerS = (Spinner)findViewById(R.id.schadensausmaß); 
    adapterS = ArrayAdapter.createFromResource(this,R.array.schadensausmaß,android.R.layout.simple_spinner_item); 
    adapterS.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); 
    spinnerS.setAdapter(adapterS); 
    spinnerS.setOnItemSelectedListener(new OnItemSelectedListener() { 
     @Override 
     public void onItemSelected(AdapterView<?> parent, View view, int position, long id) { 

     } 

     @Override 
     public void onNothingSelected(AdapterView<?> parent) { 

     } 
    }); 

    int pos1 = spinnerW.getSelectedItemPosition(); 
    int pos2 = spinnerS.getSelectedItemPosition(); 

    Toast.makeText(getBaseContext(),ergebnis(1, 2),Toast.LENGTH_LONG); 
} 


} 

完整的錯誤消息：

E/AndroidRuntime: FATAL EXCEPTION: main 
       Process: com.example.peter.myapplication, PID: 25679 
       java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.peter.myapplication/com.example.peter.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setOnItemSelectedListener(android.widget.AdapterView$OnItemSelectedListener)' on a null object reference 
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2452) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2535) 
        at android.app.ActivityThread.access$900(ActivityThread.java:154) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1380) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:148) 
        at android.app.ActivityThread.main(ActivityThread.java:5490) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
       Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setOnItemSelectedListener(android.widget.AdapterView$OnItemSelectedListener)' on a null object reference 
        at com.example.peter.myapplication.MainActivity.onCreate(MainActivity.java:58) 
        at android.app.Activity.performCreate(Activity.java:6285) 
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118) 
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2405) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2535)  
        at android.app.ActivityThread.access$900(ActivityThread.java:154)  
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1380)  
        at android.os.Handler.dispatchMessage(Handler.java:102)  
        at android.os.Looper.loop(Looper.java:148)  
        at android.app.ActivityThread.main(ActivityThread.java:5490)  
        at java.lang.reflect.Method.invoke(Native Method)  
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)  
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)  

Answer 1

更改此：

spinnerS.setOnItemSelectedListener(new OnItemSelectedListener() {...... 

有了這個：

spinnerW = (Spinner) findViewById(R.id.wahrscheinlichkeit); 
adapterW = ArrayAdapter.createFromResource(this, R.array.wahrscheinlichkeit, android.R.layout.simple_spinner_item); 
adapterW.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); 
spinnerW.setAdapter(adapterW); 

//.....here inplace of `S` put `W` 
spinnerW.setOnItemSelectedListener(new OnItemSelectedListener() { 

    @Override 
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) { 
     Toast.makeText(getBaseContext(), parent.getItemAtPosition(position) + " ausgewählt", Toast.LENGTH_LONG).show(); 
    } 

    @Override 
    public void onNothingSelected(AdapterView<?> parent) { 

    } 
});