java.lang.InstantiationException : java. lang.Class 没有零参数构造函数

Question

我正在尝试使用 timepicker 和 datepicker 制作一个表单，但遇到了这个错误。我只是一个初学者，所以请简单点。我创建了 2 个内部类 DateDialogs 和 TimeDialogs。

这是 java 类。

package com.wavedevelopers.eventsplanning;

import android.app.DatePickerDialog;
import android.app.Dialog;
import android.app.TimePickerDialog;
import android.content.Context;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v4.app.DialogFragment;
import android.support.v4.app.FragmentActivity;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.text.format.DateFormat;
import android.view.View;
import android.widget.Button;
import android.widget.DatePicker;
import android.widget.EditText;
import android.widget.TimePicker;
import android.widget.Toast;

import java.util.Calendar;

public class BookingForm extends AppCompatActivity implements DatePickerDialog.OnDateSetListener,TimePickerDialog.OnTimeSetListener {

    BackgroundWorker backgroundWorker;

    Context ctx;

    public BookingForm(Context ctx) {
        this.ctx = ctx;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_booking_form);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });



        Button doneButton = (Button) findViewById(R.id.doneButton);
        Button datePickerButton = (Button) findViewById(R.id.datePickerButton);
        Button timePickerButton = (Button) findViewById(R.id.timePickerButton);

        final EditText name = (EditText) findViewById(R.id.userNameEditText);
        final EditText cnic = (EditText) findViewById(R.id.userCNICEditText);
        final EditText phone = (EditText) findViewById(R.id.userPhoneEditText);

        doneButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                        backgroundWorker = new BackgroundWorker(ctx);
                        backgroundWorker.doInBackground(name.getText().toString(),cnic.getText().toString(),phone.getText().toString());
                        backgroundWorker.execute();
            }
        });

        datePickerButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                DateDialogs pickerDialogs = new DateDialogs();
                pickerDialogs.show(getSupportFragmentManager(),"date_picker");
            }
        });

        timePickerButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                TimeDialogs timeDialogs = new TimeDialogs();
                timeDialogs.show(getSupportFragmentManager(),"time_picker");
            }
        });



    }

    @Override
    public void onDateSet(DatePicker datePicker, int year, int monthOfYear, int dayOfMonth) {
        Toast.makeText(this,"Selected Date: " + monthOfYear + " / " + dayOfMonth + " / " + year,Toast.LENGTH_LONG).show();
    }

    @Override
    public void onTimeSet(TimePicker timePicker, int hourOfDay, int minute) {
        Toast.makeText(this,"Selected Time: " + hourOfDay + " : " + minute ,Toast.LENGTH_LONG).show();
    }

    public static class DateDialogs extends DialogFragment {

        @Override
        public Dialog onCreateDialog(Bundle savedInstanceState) {

            BookingForm bookingForm = new BookingForm(getActivity());
            Calendar calendar = Calendar.getInstance();
            int year = calendar.get(Calendar.YEAR);
            int month = calendar.get(Calendar.MONTH);
            int day = calendar.get(Calendar.DAY_OF_MONTH);


            DatePickerDialog datePickerDialog;
            datePickerDialog = new DatePickerDialog(getActivity(), bookingForm,year,month,day);

            return datePickerDialog;
        }
    }

    public static class TimeDialogs extends DialogFragment {

        @Override
        public Dialog onCreateDialog(Bundle savedInstanceState) {

            BookingForm bookingForm = new BookingForm(getActivity());
            Calendar calendar = Calendar.getInstance();
            int hour = calendar.get(Calendar.HOUR_OF_DAY);
            int min = calendar.get(Calendar.MINUTE);


            TimePickerDialog timePickerDialog;
            timePickerDialog = new TimePickerDialog(getActivity(),bookingForm,hour,min, DateFormat.is24HourFormat(getActivity()));

            return timePickerDialog;
        }
    }





}

这是错误日志。

10-04 19:28:28.278 32605-32605/com.wavedevelopers.eventsplanning E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                   Process: com.wavedevelopers.eventsplanning, PID: 32605
                                                                                   java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.wavedevelopers.eventsplanning/com.wavedevelopers.eventsplanning.BookingForm}: java.lang.InstantiationException: java.lang.Class<com.wavedevelopers.eventsplanning.BookingForm> has no zero argument constructor
                                                                                       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2337)
                                                                                       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)
                                                                                       at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                                       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354)
                                                                                       at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                       at android.os.Looper.loop(Looper.java:148)
                                                                                       at android.app.ActivityThread.main(ActivityThread.java:5443)
                                                                                       at java.lang.reflect.Method.invoke(Native Method)
                                                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
                                                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
                                                                                    Caused by: java.lang.InstantiationException: java.lang.Class<com.wavedevelopers.eventsplanning.BookingForm> has no zero argument constructor
                                                                                       at java.lang.Class.newInstance(Native Method)
                                                                                       at android.app.Instrumentation.newActivity(Instrumentation.java:1090)
                                                                                       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2327)
                                                                                       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490) 
                                                                                       at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                                                       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354) 
                                                                                       at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                                       at android.os.Looper.loop(Looper.java:148) 
                                                                                       at android.app.ActivityThread.main(ActivityThread.java:5443) 
                                                                                       at java.lang.reflect.Method.invoke(Native Method) 
                                                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728) 
                                                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 
10-04 19:28:30.855 32605-32605/com.wavedevelopers.eventsplanning I/Process: Sending signal. PID: 32605 SIG: 9

Answer 1

java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.wavedevelopers.eventsplanning/com.wavedevelopers.eventsplanning.BookingForm}: java.lang.InstantiationException: java.lang.Class<com.wavedevelopers.eventsplanning.BookingForm> has no zero argument constructor

这一行告诉我该程序希望您创建一个不带参数的类 BookingForm 的构造函数。

您可能想添加如下内容:

// Constructor with no arguments.
public BookingForm() {
    this.ctx = null;
}