帶有2個TextViews和1個按鈕的Android ListView

Question

我試圖創建一個帶有2個TextViews和1個按鈕的ListView。當用戶點擊按鈕時，活動將完成（）;並將結果傳遞給另一個視圖。我跟着this tutorial。但由於某種原因，當我點擊開始該活動時，我的應用程序崩潰了！這是來自我的應用程序的3個相關的文件。

，目錄結構數據：

public class formulasListData { 
private String formulasName; 
private String formulasDefinition; 

public formulasListData(String formulasName, String formulasDefinition) { 
    super(); 
    this.formulasName = formulasName; 
    this.formulasDefinition = formulasDefinition; 
} 

public String getFormulasName() { 
    return formulasName; 
} 

public void setFormulasName(String formulasName) { 
    this.formulasName = formulasName; 
} 

public String getFormulasDefinition() { 
    return formulasDefinition; 
} 

public void setFormulasDefinition(String formulasDefinition) { 
    this.formulasDefinition = formulasDefinition; 
    } 
} 

列表適配器：

public class formulasListAdapter extends BaseAdapter implements OnClickListener { 
private Context context; 
private List<formulasListData> formulasList; 

public formulasListAdapter(Context context, List<formulasListData> formulasList) { 
    this.context = context; 
    this.formulasList = formulasList; 
} 

@Override 
public int getCount() { 
    return formulasList.size(); 
} 

@Override 
public Object getItem(int position) { 
    return formulasList.get(position); 
} 

@Override 
public long getItemId(int position) { 

    return position; 
} 

@Override 
public View getView(int position, View rowView, ViewGroup parent) { 
    formulasListData entry = formulasList.get(position); 
    if(rowView == null) { 
     LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
     rowView = inflater.inflate(R.layout.formulas_row, null); 
    } 

    TextView formulasName = (TextView) rowView.findViewById(R.id.formulas_name); 
    formulasName.setText(entry.getFormulasName()); 

    TextView formulasDefinition = (TextView) rowView.findViewById(R.id.formulas_definition); 
    formulasDefinition.setText(entry.getFormulasDefinition()); 

    Button btnSelect = (Button) rowView.findViewById(R.id.selectFormula); 
    btnSelect.setFocusableInTouchMode(false); 
    btnSelect.setFocusable(false); 
    btnSelect.setOnClickListener(this); 

    btnSelect.setTag(entry); 

    return rowView; 
} 
@Override 

public void onClick(View view) { 
    formulasListData entry = (formulasListData) view.getTag(); 
    } 

} 

，並應顯示列表中的活動。

public class FormulasList extends Activity { 

private static final int FORMULA_0 = 0; 
private static final int FORMULA_1 = 1; 
private static final int FORMULA_2 = 2; 
private static final int FORMULA_3 = 3; 
private static final int FORMULA_4 = 4; 
private static final int FORMULA_5 = 5; 
private static final int FORMULA_6 = 6; 
// private static final int FORMULA_7 = 7; 

public void onCreate(Bundle savedInstance) { 
    super.onCreate(savedInstance); 

    ListView formulasListView = (ListView) findViewById(R.id.formulas_list); 
    formulasListView.setClickable(true); 
    final List<formulasListData> formulasList = new ArrayList<formulasListData>(); 

    final String[] formulasName = new String[] {"Circunference of a Circle:", 
           "Area of a Circle:", 
           "Volume of a Sphere:", 
           "Area Triangle:", 
           "Area Square:", 
           "Volume of a Cube:", 
           "Pithagorean Theorem:"}; 
    final String[] formulasDefinition = new String[] {"2 × π × r", 
             "π × r²", 
             "(4/3) × π × r³", 
             "(b × h)/2", 
             "side²", 
             "side³", 
             "a² + b² = c²"};   
    // formulasList.add(new formulasListData(formulasName, formulasDefinition)); 
    formulasList.add(new formulasListData(formulasName[0], formulasDefinition[0])); 
    formulasList.add(new formulasListData(formulasName[1], formulasDefinition[1])); 
    formulasList.add(new formulasListData(formulasName[2], formulasDefinition[2])); 
    formulasList.add(new formulasListData(formulasName[3], formulasDefinition[3])); 
    formulasList.add(new formulasListData(formulasName[4], formulasDefinition[4])); 
    formulasList.add(new formulasListData(formulasName[5], formulasDefinition[5])); 
    formulasList.add(new formulasListData(formulasName[6], formulasDefinition[6])); 

    SharedPreferences settings = getSharedPreferences(SettingsActivity.PREF_NAME, MODE_PRIVATE); 
    SettingsActivity.newTheme = settings.getInt("themeCustom", 0); 

    if(SettingsActivity.newTheme == SettingsActivity.THEME_DARK) { 
      setTheme(R.style.DarkTheme); 
     } else if(SettingsActivity.newTheme == SettingsActivity.THEME_LIGHT){ 
      setTheme(R.style.LightTheme); 
     } else if(SettingsActivity.newTheme == SettingsActivity.THEME_COLORS) { 
      setTheme(R.style.ColorsTheme); 
     } else { 
      setTheme(R.style.AppTheme); 
     } 
    setContentView(R.layout.activity_formulas); 

    formulasListAdapter adapter = new formulasListAdapter(this, formulasList); 

    formulasListView.setOnItemClickListener(new OnItemClickListener() { 

     @Override 
     public void onItemClick(AdapterView<?> arg0, View view, int position,long index) { 
      Intent intent= getIntent(); 
      Bundle b = new Bundle(); 
      switch (position) { 
      case FORMULA_0: 
       b.putString("key0", formulasDefinition[0]); 
       intent.putExtras(b); 
       setResult(RESULT_OK, intent); 
       finish(); 
       break; 
      case FORMULA_1: 
       b.putString("key0", formulasDefinition[1]); 
       intent.putExtras(b); 
       setResult(RESULT_OK, intent); 
       finish(); 
       break; 
      case FORMULA_2: 
       b.putString("key0", formulasDefinition[2]); 
       intent.putExtras(b); 
       setResult(RESULT_OK, intent); 
       finish(); 
       break; 
      case FORMULA_3: 
       b.putString("key0", formulasDefinition[3]); 
       intent.putExtras(b); 
       setResult(RESULT_OK, intent); 
       finish(); 
       break; 
      case FORMULA_4: 
       b.putString("key0", formulasDefinition[4]); 
       intent.putExtras(b); 
       setResult(RESULT_OK, intent); 
       finish(); 
       break; 
      case FORMULA_5: 
       b.putString("key0", formulasDefinition[5]); 
       intent.putExtras(b); 
       setResult(RESULT_OK, intent); 
       finish(); 
       break; 
      case FORMULA_6: 
       b.putString("key0", formulasDefinition[6]); 
       intent.putExtras(b); 
       setResult(RESULT_OK, intent); 
       finish(); 
       break; 
      default: 
       break; 
      }    
     } 
    });  
    formulasListView.setAdapter(adapter); 
    } 
} 

非常感謝！

編輯：這裏是logcat的

05-01 20:06:54.436: D/libEGL(4820): loaded /system/lib/egl/libEGL_tegra.so 
05-01 20:06:54.456: D/libEGL(4820): loaded /system/lib/egl/libGLESv1_CM_tegra.so 
05-01 20:06:54.466: D/libEGL(4820): loaded /system/lib/egl/libGLESv2_tegra.so 
05-01 20:06:54.486: D/OpenGLRenderer(4820): Enabling debug mode 0 
05-01 20:06:54.536: D/dalvikvm(4820): GC_CONCURRENT freed 170K, 4% free 7509K/7808K, paused 4ms+10ms, total 38ms 
05-01 20:06:59.976: D/AndroidRuntime(4820): Shutting down VM 
05-01 20:06:59.976: W/dalvikvm(4820): threadid=1: thread exiting with uncaught exception (group=0x40cde930) 
05-01 20:06:59.976: E/AndroidRuntime(4820): FATAL EXCEPTION: main 
05-01 20:06:59.976: E/AndroidRuntime(4820): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.gabilheri.marcuscalculatorv2/com.gabilheri.marcuscalculatorv2.FormulasList}: java.lang.NullPointerException 
05-01 20:06:59.976: E/AndroidRuntime(4820):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) 
05-01 20:06:59.976: E/AndroidRuntime(4820):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 
05-01 20:06:59.976: E/AndroidRuntime(4820):  at android.app.ActivityThread.access$600(ActivityThread.java:141) 
05-01 20:06:59.976: E/AndroidRuntime(4820):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 
05-01 20:06:59.976: E/AndroidRuntime(4820):  at android.os.Handler.dispatchMessage(Handler.java:99) 
05-01 20:06:59.976: E/AndroidRuntime(4820):  at android.os.Looper.loop(Looper.java:137) 
05-01 20:06:59.976: E/AndroidRuntime(4820):  at android.app.ActivityThread.main(ActivityThread.java:5041) 
05-01 20:06:59.976: E/AndroidRuntime(4820):  at java.lang.reflect.Method.invokeNative(Native Method) 
05-01 20:06:59.976: E/AndroidRuntime(4820):  at java.lang.reflect.Method.invoke(Method.java:511) 
05-01 20:06:59.976: E/AndroidRuntime(4820):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
05-01 20:06:59.976: E/AndroidRuntime(4820):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
05-01 20:06:59.976: E/AndroidRuntime(4820):  at dalvik.system.NativeStart.main(Native Method) 
05-01 20:06:59.976: E/AndroidRuntime(4820): Caused by: java.lang.NullPointerException 
05-01 20:06:59.976: E/AndroidRuntime(4820):  at com.gabilheri.marcuscalculatorv2.FormulasList.onCreate(FormulasList.java:30) 
05-01 20:06:59.976: E/AndroidRuntime(4820):  at android.app.Activity.performCreate(Activity.java:5104) 
05-01 20:06:59.976: E/AndroidRuntime(4820):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) 
05-01 20:06:59.976: E/AndroidRuntime(4820):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144) 
05-01 20:06:59.976: E/AndroidRuntime(4820):  ... 11 more 

Answer 1

嘗試移動 的setContentView（R.layout.activity_formulas）; 到方法的開始。超級通話之後。

您正在嘗試使用GUI控件初始化活動佈局