Question

我正在使用ListView来显示从我的数据库中检索到的数据，它本来可以工作，但是突然不显示任何东西。通常，它应该显示类似以下内容（其他项目的屏幕截图）：

编辑后，发布我的所有代码：

public class MainActivity extends AppCompatActivity {

private TextView mTextMessage;

String[] dataDetail;
ArrayList<dataDetail> allDetail = new ArrayList<>();

ListView detailList;
final Context context = this;

final int min = 0;
final int max = 10;
final int random = new Random().nextInt((max - min) + 1) + min;

int score = 0;

private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
        = new BottomNavigationView.OnNavigationItemSelectedListener() {

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()) {
            case R.id.navigation_home:
                mTextMessage.setText(R.string.title_home);
                return true;
            case R.id.navigation_dashboard:
                mTextMessage.setText(R.string.title_dashboard);
                return true;
        }
        return false;
    }
};

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

    detailList = findViewById(R.id.dataView);

    mTextMessage = (TextView) findViewById(R.id.message);
    BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);
    navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);

    new GetData().execute();

}

private class GetData extends AsyncTask<Void, Void, ArrayList<dataDetail>> {

    protected ArrayList<dataDetail> doInBackground(Void... voids) {

        HttpURLConnection urlConnection;
        InputStream in = null;
        try {
            URL url = new URL("http://10.0.2.2:8080/projectServer/DataDetailDB?getdata=true");
            urlConnection = (HttpURLConnection) url.openConnection();
            in = new BufferedInputStream(urlConnection.getInputStream());
        } catch (IOException e) {
            e.printStackTrace();
        }
        String response = convertStreamToString(in);
        System.out.println("Server response = " + response);

        try {
            JSONArray jsonArray = new JSONArray(response);
            dataDetail = new String[jsonArray.length()];

            for (int i = 0; i < jsonArray.length(); i++) {

               final String customerName = jsonArray.getJSONObject(i).get("customerName").toString();
               final String carName = jsonArray.getJSONObject(i).get("carName").toString();
               final String appointmentDate = jsonArray.getJSONObject(i).get("appointmentDate").toString();
               final String email = jsonArray.getJSONObject(i).get("email").toString();
               final String issueDescribe = jsonArray.getJSONObject(i).get("issueDescribe").toString();
               final String timeForJob = jsonArray.getJSONObject(i).get("timeForJob").toString();
               final String costForJob = jsonArray.getJSONObject(i).get("costForJob").toString();
               final String reliableOnCar = jsonArray.getJSONObject(i).get("reliableOnCar").toString();
               final String distanceJob = jsonArray.getJSONObject(i).get("distance").toString();
               final int finalScore = score;

                if (random * Float.parseFloat(timeForJob) < 15) {
                    score += 1;
                } if (random * Float.parseFloat(reliableOnCar) > 15) {
                    score += 1;
                } if (random * Float.parseFloat(distanceJob) > 10) {
                    score -=1;
                } if (random * Float.parseFloat(costForJob) > 40) {
                    score -=1;
                } if(random * Float.parseFloat(timeForJob) + random * Float.parseFloat(reliableOnCar) +
                        random * Float.parseFloat(distanceJob) + random * Float.parseFloat(costForJob) > 500) {
                    score += 5;
                } else {
                    score += 0;
                }


                dataDetail tData = new dataDetail(customerName, carName, appointmentDate, email, issueDescribe, timeForJob, costForJob, reliableOnCar, distanceJob, finalScore);
                allDetail.add(tData);

                System.out.println("customername = " + customerName + ", Score = " + finalScore);

                if (score >= 5) {
                    dataDetail[i] = "Name: " + customerName + "\n" + "Appointment Date: " + appointmentDate + "\n" + "Urgent";
                } else if (score >= 3) {
                    dataDetail[i] = "Name: " + customerName + "\n" + "Appointment Date: " + appointmentDate + "\n" + "Second urgent";
                } else {
                    dataDetail[i] = "Name: " + customerName + "\n" + "Appointment Date: " + appointmentDate + "\n" + "Normal";
                }

                System.out.print("Debug: " + dataDetail);

                Collections.sort(allDetail, new Comparator<advprog.mmu.ac.uk.schedulerapp.dataDetail>() {
                    @Override
                    public int compare(dataDetail o1, dataDetail o2) {
                        return Integer.compare(o1.getFinalScore(), o2.getFinalScore());
                    }
                });

                Collections.reverse(allDetail);

            }

        } catch (JSONException e) {
            e.printStackTrace();
        }

        return null;
    }

    protected void onPostExecute(ArrayList<dataDetail> dataDetailArrayList) {
        super.onPostExecute(dataDetailArrayList);

        ArrayAdapter List = new ArrayAdapter(context, android.R.layout.simple_list_item_1, allDetail);
        detailList.setAdapter(List);
    }
}

public String convertStreamToString(InputStream is) {
    java.util.Scanner s = new java.util.Scanner(is).useDelimiter("\\A");
    return s.hasNext() ? s.next() : "";
}}

dataDetial类：

公共类dataDetail {

private String customerName;

private String carName;
private String appointmentDate;
private String email;
private String issueDescribe;
private String timeForJob;
private String costForJob;
private String reliableOnCar;
private String distanceJob;
private int finalScore;

public dataDetail(String customerName, String carName, String appointmentDate, String email, String issueDescribe, String timeForJob, String costForJob, String reliableOnCar, String distanceJob, int finalScore) {
    this.customerName = customerName;
    this.carName = carName;
    this.appointmentDate = appointmentDate;
    this.email = email;
    this.issueDescribe = issueDescribe;
    this.timeForJob = timeForJob;
    this.costForJob = costForJob;
    this.reliableOnCar = reliableOnCar;
    this.distanceJob = distanceJob;
    this.finalScore = finalScore;
}

public int getFinalScore() {
    return finalScore;
}

public void setFinalScore(int finalScore) {
    this.finalScore = finalScore;
}

public String getCustomerName() {
    return customerName;
}

public void setCustomerName(String customerName) {
    this.customerName = customerName;
}

public String getCarName() {
    return carName;
}

public void setCarName(String carName) {
    this.carName = carName;
}

public String getAppointmentDate() {
    return appointmentDate;
}

public void setAppointmentDate(String appointmentDate) {
    this.appointmentDate = appointmentDate;
}

public String getEmail() {
    return email;
}

public void setEmail(String email) {
    this.email = email;
}

public String getIssueDescribe() {
    return issueDescribe;
}

public void setIssueDescribe(String issueDescribe) {
    this.issueDescribe = issueDescribe;
}

public String getTimeForJob() {
    return timeForJob;
}

public void setTimeForJob(String timeForJob) {
    this.timeForJob = timeForJob;
}

public String getCostForJob() {
    return costForJob;
}

public void setCostForJob(String costForJob) {
    this.costForJob = costForJob;
}

public String getReliableOnCar() {
    return reliableOnCar;
}

public void setReliableOnCar(String reliableOnCar) {
    this.reliableOnCar = reliableOnCar;
}

public String getDistanceJob() {
    return distanceJob;
}

public void setDistanceJob(String distanceJob) {
    this.distanceJob = distanceJob;
} }

我认为这行dataDetail [i] =“名称：” +客户名称+“ \ n” +“约会日期：” +约会日期+“ \ n” +“紧急”；将显示我想在ListView中显示的数据，但它显示的数据是这样的：

当我尝试打印出dataDetail时，在logcat中它给出了以下信息：

I / System.out：customername = Josh，分数= 0 调试：[Ljava.lang.String; @ e883626customername = Wolski，分数= 1 I / System.out：调试：[Ljava.lang.String; @ e883626customername = Cardinal，Score = 2 I / System.out：调试：[Ljava.lang.String; @ e883626customername = Pang，Score = 3

Answer 1

由于您使用的是默认的ArrayAdapter，因此正在呈现toString()类的dataDetail。您至少有以下选择：

在toString()中定义自定义dataDetail，以显示所需的信息。像这样：

@Override 公共字符串toString（）{ 返回“名称：” + carName; }

为了显示汽车名称。
定义并使用自定义适配器，您可以在其中使用自定义视图持有者来呈现所需的数据。如果您使用的是RecyclerView，请参见here。
您也可以扩展ArrayAdapter。有关更多详细信息，请参见此answer。

我建议您使用带有自定义适配器的RecyclerView，而不是ListView，它类似于here。这样，您将获得很大的灵活性，并且您的应用程序将能够高效地呈现很多元素。参见here，两者之间有一个很好的比较。

Answer 2

 dataDetail tData = new dataDetail(customerName, carName, appointmentDate, email, issueDescribe, timeForJob, costForJob, reliableOnCar, distanceJob, finalScore);
            allDetail.add(tData.getCustomerName());

arrya适配器仅使用字符串类型数组列表，因此它将tdata作为字符串放入allDetails中

我的ListView不显示我的数据，但显示我的包名称

2 个答案: