的Android設置的TextView從其他類

Question

我有代碼：

LinearLayout primaryFieldsView = (LinearLayout) findViewById(R.id.mainLayout); 
     for(int j=0; j<5; j++){ 
      TextView text = new TextView(this); 
      text.setText("The Value of i is :"); // <-- does it really compile without the + sign? 
      text.setTextSize(12); 
      text.setGravity(Gravity.LEFT); 
      text.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT)); 
      primaryFieldsView.addView(text); 
      } 

我想，這段代碼是從另一個類調用，例如： 在主類：

new PrimaryFieldsView().setPrimaryFields(); 

其他類：

public class PrimaryFieldsView extends Activity{ 

    public void setPrimaryFields(){ 

     LinearLayout primaryFieldsView = (LinearLayout) findViewById(R.id.mainLayout); 
     for(int j=0; j<5; j++){ 
      TextView text = new TextView(this); 
      text.setText("The Value of i is :"); // <-- does it really compile without the + sign? 
      text.setTextSize(12); 
      text.setGravity(Gravity.LEFT); 
      text.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT)); 
      primaryFieldsView.addView(text); 
      } 



    } 

當我把這個代碼放在Main類的工作中：

 LinearLayout primaryFieldsView = (LinearLayout) findViewById(R.id.mainLayout); 
     for(int j=0; j<5; j++){ 
      TextView text = new TextView(this); 
      text.setText("The Value of i is :"); // <-- does it really compile without the + sign? 
      text.setTextSize(12); 
      text.setGravity(Gravity.LEFT); 
      text.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT)); 
      primaryFieldsView.addView(text); 
      } 

在這一刻，我有錯誤

10-27 21:32:58.389: E/AndroidRuntime(2907): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.passreader/com.example.passreader.views.CouponView}: java.lang.NullPointerException 

Answer 1

public void setPrimaryFields(Activity activity) 
    { 
     LinearLayout primaryFieldsView = (LinearLayout) activity.findViewById(R.id.mainLayout); 
     for(int j=0; j<5; j++){ 
      TextView text = new TextView(this); 
      text.setText("The Value of i is :"); // <-- does it really compile without the + sign? 
      text.setTextSize(12); 
      text.setGravity(Gravity.LEFT); 
      text.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT)); 
      primaryFieldsView.addView(text); 
      } 
    } 

主：

setPrimaryFields(this); 

PrimaryFieldsView類不必雖然延長任何東西。