如何根据片段和创建顺序来管理片段和活动？

Question

我想做什么

我想从Fragment调用Activity，以在Android应用程序中同时实现片段和活动之间的转换。

我已经成功地从片段文件中调用了活动文件上的一种特定方法，但是在从片段中调用整个活动时遇到了麻烦。

SampleFragment - MainActivity's fragmentMethod() is called once  the button is clicked on the page
Sample1Fragment - FormActivity is called once the button is clicked on the page
FormActivity - FormActivity2 is called once the button is clicked on the page

以上与我以前的问题相同：How can I fix the code to call Activity from Fragment in Android App?

错误和问题

成功构建了一个项目并在模拟器上运行该应用程序。但是，当我单击按钮以调用Sample1Fragment上的FormActivity时，屏幕突然关闭。

我无法解决此问题。

Sample1Fragment.kt上以下部分的错误消息

Modifier 'override' is not applicable to 'local function'

Sample1Fragment.kt

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)

        override fun onViewCreated(view: View, savedInstanceState: Bundle) {
            btnClick2.setOnClickListener(object:View.OnClickListener{

                // here I would like to move to FormActivity
                override fun onClick(v: View?) {
                    activity?.startActivity(Intent(context, FormActivity::class.java))
                }

            })
        }

当前代码

MainActivity.kt

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Toast
import androidx.fragment.app.Fragment
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        // make the list of fragment
        val fragmentList = arrayListOf<Fragment>(
            SampleFragment(),
            Sample1Fragment()
        )

        // create instance of adapter
        val adapter = SamplePagerAdapter(supportFragmentManager, fragmentList)
        /// set adapter
        viewPager.adapter = adapter
    }



    public fun fragmentMethod() {
        Toast.makeText(this@MainActivity, "Method called From Fragment", Toast.LENGTH_LONG).show();
    }
}

SampleFragment.kt

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import kotlinx.android.synthetic.main.fragment_sample.*

class SampleFragment : Fragment() {


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {

        }
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_sample, container, false)
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        btnClick.setOnClickListener(object:View.OnClickListener{
            override fun onClick(v: View?) {
                (activity as MainActivity).fragmentMethod()
            }

        })
    }



}

Sample1Fragment.kt

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import kotlinx.android.synthetic.main.fragment_sample1.*
import android.content.Intent

class Sample1Fragment : Fragment() {

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_sample1, container, false)
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)

        override fun onViewCreated(view: View, savedInstanceState: Bundle) {
            btnClick2.setOnClickListener(object:View.OnClickListener{

                // here I would like to move to FormActivity
                override fun onClick(v: View?) {
                    activity?.startActivity(Intent(context, FormActivity::class.java))
                }

            })
        }

    }

}

开发环境

Android Studio 3.6.1

我尝试做的事情

ListViewModel.kt

package com.example.fragact

import android.app.usage.UsageEvents
import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel

class ListViewModel : ViewModel() {
    private val _navigateToDetails = MutableLiveData<UsageEvents.Event<String>>()

    val navigateToDetails : LiveData<UsageEvents.Event<String>>
        get() = _navigateToDetails


    fun userClicksOnButton(itemId: String) {
        _navigateToDetails.value =
            UsageEvents.Event(itemId)  // Trigger the event by setting a new Event as a new value
    }
}

Sample1Fragment.kt

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import kotlinx.android.synthetic.main.fragment_sample1.*
import android.content.Intent


class Sample1Fragment : Fragment() {

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_sample1, container, false)
    }

    myViewModel.navigateToDetails.observe(this, Observer {
        it.getContentIfNotHandled()?.let { // Only proceed if the event has never been handled
            startActivity(DetailsActivity...)
        }
    })

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)

        override fun onViewCreated(view: View, savedInstanceState: Bundle) {
            btnClick2.setOnClickListener(object:View.OnClickListener{

                // here I would like to move to FormActivity
                override fun onClick(v: View?) {
                    activity?.startActivity(Intent(context, FormActivity::class.java))
                }

            })
        }

    }

}

Answer 1

在Sample1Fragment.kt中，您将覆盖onViewCreated() 内部 onActivityCreated()方法。这就是为什么你得到

修饰符“替代”不适用于“本地功能”

关于导航：有几种方法可以在不同的活动和片段之间进行导航：

1. navigation，通常最容易实现
2. [callbacks，当您在Android Studio中创建片段时已预先设置]
3. view model，在片段及其活动之间共享。在这种情况下，建议使用SingleLiveEvent触发事件。