Question

在Swift 4.0的Firebase快照字典中获取值时，我无法解开可选的nil

这是我的代码

public class ReportDetailsActivity extends Activity {

        private ArrayList<Hemoglobin> hemoglobins;
        private GraphView graph;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_report_details);


            graph =  findViewById(R.id.graph);

    DoingNetworkStuff(Endpoints.BASE_URL+Endpoints.GET_HEMOGLOBIN_READINGS);
//Here It is working
            DoTheGraphs();


        }

        private void DoingNetworkStuff(String url) {
            final String TAG = "ReportsActivity_DoingNetworkStuff";
            final ProgressDialog pDialog = new ProgressDialog(this);
            pDialog.setMessage("Loading...");
            pDialog.show();
            StringRequest postRequest = new StringRequest(Request.Method.POST, url,
                    new Response.Listener<String>() {
                        @Override
                        public void onResponse(String response) {
                            try {
                                hemoglobins = new ArrayList<>();
                                JSONArray jsonResponse = new JSONObject(response).getJSONArray("info");

                                for (int i = 0; i < jsonResponse.length(); i++) {
                                    JSONObject obj = jsonResponse.getJSONObject(i);
                                    String date = obj.optString("lappointmentdate");
                                    String value = obj.optString("lhemoglobinreading");

                                    hemoglobins.add(new Hemoglobin(date,value));
                                }

//This is where I need to call DoTheGraphs(), but not working.



                            } catch (JSONException e) {
                                e.printStackTrace();
                            }
                            pDialog.dismiss();
                        }
                    },
                    new Response.ErrorListener() {
                        @Override
                        public void onErrorResponse(VolleyError error) {
                            VolleyLog.d(TAG, "Error: " + error.getMessage());
                            // hide the progress dialog
                            pDialog.hide();
                            pDialog.setMessage("Check your internet connection Technical Difficulties!");
                            pDialog.show();
                            Handler handler = new Handler();
                            handler.postDelayed(new Runnable() {
                                public void run() {
                                    pDialog.dismiss();
                                }
                            }, 5000);
                        }
                    }

            ) {
                @Override
                protected Map<String, String> getParams() {

                    Map<String, String> params = new HashMap<>();
                    // the POST parameters:
                    params.put("patientid", "VIU1111111111433");
                    params.put("patientdependantid", "");
                    return params;
                }
            };
            Volley.newRequestQueue(this).add(postRequest);
        }


        private void DoTheGraphs() {

            Date d1 = null;
            Date d2 = null;
            Date d3 = null;
            SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy");
            try {
                d1 = formatter.parse("03/09/1995");
                d2 = formatter.parse("04/09/1995");
                d3 = formatter.parse("05/09/1995");
            } catch (ParseException e) {
                e.printStackTrace();
            }
            Date[] date = {d1,d2,d3};
            DataPoint[] dataPoints = new DataPoint[3];
            for(int i=0;i<3;i++){
                dataPoints[i]=new DataPoint(date[i],1);//new DataPoint(hemoglobins.get(i).getDate(), hemoglobins.get(i).getValue());
            }

            LineGraphSeries<DataPoint> series = new LineGraphSeries<>(dataPoints);

            graph.addSeries(series);

            graph.getGridLabelRenderer().setLabelFormatter(new DateAsXAxisLabelFormatter(ReportDetailsActivity.this));
            graph.getGridLabelRenderer().setNumHorizontalLabels(3); // only 4 because of the space

            graph.getViewport().setMinX(date[0].getTime());
            graph.getViewport().setMaxX(date[2].getTime());
            graph.getViewport().setXAxisBoundsManual(true);

            graph.getGridLabelRenderer().setHumanRounding(false);


        }
    }

当我运行它时，它给我一个错误：

线程1：致命错误：展开包装时意外发现nil 可选值

我也在Xcode 9.0的Swift 4.0中编写此代码

任何人都可以帮我几个礼拜了

非常感谢您的帮助

Answer 1

如果您需要这两个值来继续执行，我建议您使用guard，这样您就可以使它们排成一行，并避免缩进，以便于阅读。

defer { print(self.questions.count) }

guard let dict = snapshot.value as? NSDictionary else { return }
guard let questionTitle = dict["name"] as? String else { return }
guard let created_by = dict["email"] as? String else { return }

let question = Question(questionName: questionTitle, created_by: created_by)
self.questions.append(question)

Answer 2

只需将下面的代码替换为您的代码即可。

let questionTitle = dict["name"] as? String ?? ""
let created_by = dict["email"] as? String ?? ""

它将为您工作。

在Swift 4.0中从Firebase快照字典中获取值时解开可选的nil

2 个答案: