在Android中关闭警报对话框后，为什么不进步旋转器工作

Question

我的进度栏只是一个旋转器。

我正在向用户显示两个选项，当用户单击一个选项时，我会显示一个对话框，以便用户读取并理解它。

这就是我想要的。当他们单击正面时，它应该显示旋转器并在后台保持呼叫服务。当他们单击负面时，应该使该选项不选中。

这是代码。

此radiogroup.setonclicklistener进入片段的onCreateview方法。

    public class Choose_CountryFragment extends Fragment {
        private RadioGroup radioGroup;
        private TextView textView;
        private String countryChosen = null;
        ConnectionStatus connectionStatus = new ConnectionStatus(getContext());
        public Choose_CountryFragment() {
        }
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 final Bundle savedInstanceState) {
            View rootView =  inflater.inflate(R.layout.fragment_choose__country, container, false);
          radioGroup = (RadioGroup) rootView.findViewById(R.id.country_choice_radio);
         radioGroup.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener()
                {
                    public void onCheckedChanged(RadioGroup group, int checkedId) {
                        switch(checkedId){
                            case R.id.countryCanada:
                                // do operations specific to this selection
                                countryChosen = "Canada";
                                Intent explicitServiceIntent = new Intent(getActivity(), Service.class);
                                explicitServiceIntent.putExtra("country", "Canada");
                                getActivity().startService(explicitServiceIntent);
                                connectionStatus.showProgress();
                                break;
                            case R.id.countryUSA:
                                countryChosen = "USA";
                                Dialog dialog = onCreateDialog(savedInstanceState);
                                dialog.show();
                                connectionStatus.showProgress();
                                break;
                        }
                    }
                });
        public Dialog onCreateDialog(final Bundle savedInstanceState) {
            // Use the Builder class for convenient dialog construction
            AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
            Toast.makeText(getContext(), "Click Got it", Toast.LENGTH_LONG).show();
            builder.setMessage(R.string.SignUpWarningInfo)
                    .setPositiveButton(R.string.gotIt, new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int id) {
                            Intent explicitServiceIntentUSA = new Intent(getActivity(), Service.class);
                            explicitServiceIntentUSA.putExtra("country", countryChosen );
                            getActivity().startService(explicitServiceIntentUSA);
                        }
                    })
                    .setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int id) {                        
                            return;
                        }
                    });
            // Create the AlertDialog object and return it
            return builder.create();
        }
    }
}

connectionstatus.java

public class ConnectionStatus {
    private Context _context;
    private ProgressDialog progressDialog = null;
    public ConnectionStatus(Context context) {
        this._context = context;
    }
    public void showProgress(){
            progressDialog = new ProgressDialog(_context);
            progressDialog.setCancelable(false);
            progressDialog.setIndeterminate(true);
            progressDialog.show();
        }
}

当我单击美国时发生错误。错误我得到

         java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources$Theme android.content.Context.getTheme()' on a null object reference
                  at android.app.AlertDialog.resolveDialogTheme(AlertDialog.java:154)
                  at android.app.AlertDialog.<init>(AlertDialog.java:109)
                  at android.app.ProgressDialog.<init>(ProgressDialog.java:77)
                  at com.a2.a2.ConnectionStatus.showProgress(ConnectionStatus.java:66)
                  at com.a2.a2.signUp.Choose_CountryFragment$1.onCheckedChanged(Choose_CountryFragment.java:73)

Answer 1

您的Context返回null

在中更改代码> select_countryfragment

public class Choose_CountryFragment extends Fragment {
    ...
   protected Context mContext;
   private ConnectionStatus connectionStatus
   ...
    public Choose_CountryFragment() {
    }
      @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             final Bundle savedInstanceState) {
        View rootView =  inflater.inflate(R.layout.fragment_choose__country, container, false);
       ...
       connectionStatus = new ConnectionStatus(mContext);// initialize ConnectionStatus here
       ...
    }
}

Override onattach Choose_CountryFragment

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

Answer 2

在Fragment中，您必须使用：

ProgressDialog progressDialog = new ProgressDialog(getActivity);

从文档中，getActivity()方法返回Activity此Fragment当前与之关联。

编辑：在Activity类中，您必须使用：

ProgressDialog progressDialog = new ProgressDialog(YourActivityClassName.this);