为什么在 android 中关闭警告对话框后进度微调器不工作？

Question

我的进度条只是一个旋转器。

我向用户展示了两个选项，当用户点击一个选项时，我展示了一个对话框，以便用户阅读并理解它。

这就是我想要的。当他们点击肯定时，它应该显示微调器并继续在后台调用服务。当他们单击否定时，应该取消选中该选项。

这是代码。

这个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();
        }
}

点击美国时出现错误。我得到的错误

         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.onCheckedChanged(Choose_CountryFragment.java:73)

Answer 1

在Fragment中，您必须使用：

ProgressDialog progressDialog = new ProgressDialog(getActivity);

来自 documentation，getActivity() 方法 returns Activity 此 Fragment 当前与其关联。

编辑：在 Activity class 中，你必须使用 like:

ProgressDialog progressDialog = new ProgressDialog(YourActivityClassName.this);

Answer 2

你的Context返回null

更改 Choose_CountryFragment 中的代码

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
       ...
    }

}

覆盖 onAttach 内部 Choose_CountryFragment

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

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