考虑到创建顺序，我如何管理片段和活动？

Question

我想做什么

我想从片段中调用活动，在Android应用程序中实现片段之间的转换和同时进行的活动。

我已经成功地从片段文件中调用了一个特定的活动文件方法，但是我在从片段调用整个活动时遇到了困难。

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

上面的问题与我以前的问题相同：我如何在Android中修复从片段调用活动的代码？

错误与问题

它成功地构建了一个项目并在模拟器上运行了该应用程序。但是，当我单击按钮在Sample1Fragment上调用Sample1Fragment时，屏幕突然关闭。

我很难解决这个问题。

Sample1Fragment.kt上下面部分的错误消息

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 3.6.1

我想做的事

它尝试使用SingleLiveEvent推荐的答案，但我还没有找到在当前代码ListViewModel.kt和Sample1Fragment.kt上实现它的适当方法。

参考资料：LiveData与SnackBar、导航和其他事件( SingleLiveEvent案例)

ListViewModel.kt

import android.app.usage.UsageEvents
import android.os.Build
import androidx.annotation.RequiresApi
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


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

这些是我要面对的错误信息

​

​

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
        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))
                }

            })
        }
    })

    }

}

这是我要面对的错误信息

​

​

Answer 1

在Sample1Fragment.kt中，您要在 onActivityCreated()方法中重写onViewCreated() 。

这就是为什么你

修饰符“覆盖”不适用于“本地函数”

关于导航:有几种可能的方法可以在不同的活动和片段之间导航：

1. 导航，这通常是最容易实现的。
2. 回调，当您在Android中创建片段时已经预先设置了
3. 视图模型，在片段和它的活动之间共享。在这种情况下，我建议使用SingleLiveEvent来触发事件。