Question

我刚刚开始学习Kotlin，我的当前目标是在按下按钮后在片段中创建一个简单的日期选择器。

作为指导，我使用了示例，显示为android developer docs for pickers。作为模板，我使用了底部导航标准模板。

我的问题：根据示例，我创建了一个类DatePickerFragment。在返回行中，引用了需要上下文作为输入的方法。在示例中，写了activity。我不知道在这里实现什么才能使代码正常工作。

错误消息（指的是DatePickerFragment类）：

'onCreateDialog'不会覆盖任何内容
类型不匹配：推断的类型为FragmentActivity？但是希望有上下文

在下面，我粘贴一些代码。整个代码也可以在这里找到： https://github.com/andregreschat/DatePickerinFragmentTest

DatePickerFragment类别：

package de.datepickerinfragmenttest

import android.app.DatePickerDialog
import android.app.Dialog
import android.os.Bundle
import android.view.View
import android.widget.DatePicker
import androidx.fragment.app.DialogFragment
import java.util.*

class DatePickerFragment : DialogFragment(), DatePickerDialog.OnDateSetListener {

    override fun onCreateDialog(savedInstanceState: Bundle): Dialog {
        // Use the current date as the default date in the picker
        val c = Calendar.getInstance()
        val year = c.get(Calendar.YEAR)
        val month = c.get(Calendar.MONTH)
        val day = c.get(Calendar.DAY_OF_MONTH)

        // Create a new instance of DatePickerDialog and return it
        return DatePickerDialog(activity, this, year, month, day)
    }

    override fun onDateSet(view: DatePicker, year: Int, month: Int, day: Int) {
        // Do something with the date chosen by the user


    }
}

MainActivity

package de.datepickerinfragmenttest

import android.os.Bundle
import android.view.View
import com.google.android.material.bottomnavigation.BottomNavigationView
import androidx.appcompat.app.AppCompatActivity
import androidx.navigation.findNavController
import androidx.navigation.ui.AppBarConfiguration
import androidx.navigation.ui.setupActionBarWithNavController
import androidx.navigation.ui.setupWithNavController

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val navView: BottomNavigationView = findViewById(R.id.nav_view)

        val navController = findNavController(R.id.nav_host_fragment)
        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        val appBarConfiguration = AppBarConfiguration(setOf(
                R.id.navigation_home, R.id.navigation_dashboard, R.id.navigation_notifications))
        setupActionBarWithNavController(navController, appBarConfiguration)
        navView.setupWithNavController(navController)

        fun showDatePickerDialog(v: View) {
            val newFragment = DatePickerFragment()
            newFragment.show(supportFragmentManager, "datePicker")
        }

    }


}

片段：

package de.datepickerinfragmenttest.ui.home

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import androidx.fragment.app.Fragment
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProviders
import de.datepickerinfragmenttest.DatePickerFragment
import de.datepickerinfragmenttest.R
import androidx.fragment.app.FragmentManager

class HomeFragment : Fragment() {

    private lateinit var homeViewModel: HomeViewModel

    override fun onCreateView(
            inflater: LayoutInflater,
            container: ViewGroup?,
            savedInstanceState: Bundle?
    ): View? {
        homeViewModel =
                ViewModelProviders.of(this).get(HomeViewModel::class.java)
        val root = inflater.inflate(R.layout.fragment_home, container, false)
        val textView: TextView = root.findViewById(R.id.text_home)
        homeViewModel.text.observe(viewLifecycleOwner, Observer {
            textView.text = it
        })
        return root
    }
}

使用按钮的片段布局

    <?xml version="1.0" encoding="utf-8"?>
    <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".ui.home.HomeFragment">

        <TextView
            android:id="@+id/text_home"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginStart="8dp"
            android:layout_marginTop="8dp"
            android:layout_marginEnd="8dp"
            android:textAlignment="center"
            android:textSize="20sp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <Button
            android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="SetDate"
            app:layout_constraintBottom_toTopOf="@+id/text_home"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            android:onClick="showDatePickerDialog"/>
    </androidx.constraintlayout.widget.ConstraintLayout>

Answer 1

我有点想知道您正在设置navigation组件，但是没有使用它来移动到DialogFragment。

在实例化对话框时，可能还需要调用其他2种方法（而不是此activity属性）：

Context
requireContext()（如果您需要确保通过了活动requireActivity()）

在片段中创建日期选择器

1 个答案: