Question

我有一些显示平均值的TextView，然后我有一个类有AlertDialog方法，我希望用户点击确定并更新我的TextView值。

我收到错误显示java.lang.NullPointerException:

有人可以教我如何解决它并完成我想要的事情，提前谢谢。

TextView布局类扩展了Fragment：

    public class MyDailyInput extends Fragment implements View.OnClickListener{

        private Context context;

    @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View view = inflater.inflate(R.layout.fragment_my_daily_input, container, false);
//contact is my data object , it has data i'm sure.
new DialogHandler(getActivity()).
                                updateDialog(getResources().getString(R.string.update),
                                        getResources().getString(R.string.cancel), contact);


            return view;
    }

        // Set the average value method
        public void setAverageValue(Context context){
            avBeMorning.setText(String.valueOf(av.beforeMorning()));
            avAfMorning.setText(String.valueOf(av.afterMorning()));
            avBeNoon.setText(String.valueOf(av.beforeNoon()));
            avAfNoon.setText(String.valueOf(av.afterNoon()));
            avBeNight.setText(String.valueOf(av.beforeNight()));
            avAfNight.setText(String.valueOf(av.afterNight()));
        }

这是我的类控制AlertDialog：

public class DialogHandler extends AppCompatActivity {

    private DatabaseHandler db =null;
    private Context context;

    public DialogHandler(Context context){
        this.context = context;
        db = new DatabaseHandler(context);
    }

    // AlertDialog
    public void updateDialog(String rightMessage, String leftMessage, final Contact contact) {
        android.support.v7.app.AlertDialog.Builder builder = new android.support.v7.app.AlertDialog.Builder(context);
        builder.setMessage(context.getResources().getString(R.string.dataExisted))
                .setPositiveButton(rightMessage, new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialogInterface, int i) {
                        System.out.println("try to update");
                        Toast.makeText(context,context.getResources().getString(R.string.updatedSucceed),Toast.LENGTH_SHORT).show();
                        db.updateContact(contact);
                        // I try to use this code to 
                        // change my TextView value of 
                        // MyDailyInut layout , but i get error.
                        new MyDailyInput().setAverageValue(context);
                    }
                });
        builder.setNegativeButton(leftMessage, new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialogInterface, int i) {

            }
        });
        builder.show();
    }

}

Answer 1

你必须在fragment中创建一个接口，activity应该实现该接口的方法并在fragment的onCreate方法上初始化接口。

//片段

  public class FragmentOne extends Fragment {
     private OnClicked call;

     public interface OnClicked {
        void gotoActivity(int value);
     }

    @Override
    public void onAttach(Context context){
    super.onAttach(context);
    call = (OnClicked) context;
}

    //any event
    call.gotoActivity(your average value);
   }


  public class RandomActivity extends Activity implements FragmentOne.OnClicked {

   @Override
   public void gotoActivity(int value) {
    // do here
   }
  }

Answer 2

在片段本身内创建alertDialog而不是创建新活动

使用getActivity()代替context

    public class MyDailyInput extends Fragment implements View.OnClickListener{

        private Context context;

    @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View view = inflater.inflate(R.layout.fragment_my_daily_input, container, false);

                                updateDialog(getResources().getString(R.string.update),
                                        getResources().getString(R.string.cancel), contact);


            return view;
    }

        // Set the average value method
        public void setAverageValue(Context context){
            avBeMorning.setText(String.valueOf(av.beforeMorning()));
            avAfMorning.setText(String.valueOf(av.afterMorning()));
            avBeNoon.setText(String.valueOf(av.beforeNoon()));
            avAfNoon.setText(String.valueOf(av.afterNoon()));
            avBeNight.setText(String.valueOf(av.beforeNight()));
            avAfNight.setText(String.valueOf(av.afterNight()));
        }





public void updateDialog(String rightMessage, String leftMessage, final Contact contact) {
        android.support.v7.app.AlertDialog.Builder builder = new android.support.v7.app.AlertDialog.Builder(getActivity());
        builder.setMessage(getActivity().getResources().getString(R.string.dataExisted))
                .setPositiveButton(rightMessage, new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialogInterface, int i) {
                        System.out.println("try to update");
                        Toast.makeText(getActivity(),getActivity().getResources().getString(R.string.updatedSucceed),Toast.LENGTH_SHORT).show();
                        db.updateContact(contact);
                        // I try to use this code to 
                        // change my TextView value of 
                        // MyDailyInut layout , but i get error.
                       setAverageValue(getActivity());
                    }
                });
        builder.setNegativeButton(leftMessage, new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialogInterface, int i) {

            }
        });
        builder.show();
    }

如何从另一个类控制布局？

2 个答案: