Kotlin: AppCompatActivity片段

Question

将AppCompatActivity()转换为Fragment()，并根据主题进行了一些更改：如何将AppCompatActivity更改为片段并更新了Gradle has本机:不幸的是，应用程序已经停止。

在我创建片段视图之前，carouselView就已经工作了。它汇编：

执行任务:app:assembleDebug in project /Users/jaskier/Documents/Android/GoodTogether配置项目:应用警告:不再推荐‘kotlin扩展’Gradle插件。请使用此迁移指南(https://goo.gle/kotlin-android-extensions-deprecation)开始使用视图绑定(https://developer.android.com/topic/libraries/view-binding)和kotlin插件。配置项目:选项卡视图警告：‘kotlin-android-扩展’Gradle插件是不推荐的。请使用此迁移指南(https://goo.gle/kotlin-android-extensions-deprecation)开始使用视图绑定(https://developer.android.com/topic/libraries/view-binding)和kotlin插件。任务:app:packageDebugRenderscript :app:preDebugBuild最新任务:tabview:预览:preDebugBuild最新任务:tabview :tabview:preDebugBuild最新任务:tabview:packageDebugRenderscript NO-SOURCE Task :app:generateDebugBuildConfig -TO日期任务:app:compileDebugRenderscript NO-SOURCE Task :tabview:compileDebugAidl NO-SOURCE Task :app:generateDebugResValues TO-DATE任务:app:generateDebugResValues TO日期任务:app:generateDebugResValues generateDebugResources任务:tabview:generateDebugResources最新任务:tabview:packageDebugResources最新任务:app:mergeDebugResources最新任务:app:createDebugCompatibleScreenManifests最新任务:app:extractDeepLinksDebug UP- Task任务:tabview:extractDeepLinksDebug UP-日期任务:tabview:processDebugManifest -TO-日期任务:app:processDebugManifest UP-TO-DATE任务:tabview:parseDebugLocalResources UP-DATE任务:tabview:extractDeepLinksDebug Task :DATE:DATE UP- Task任务任务:tabview:generateDebugBuildConfig最新任务:tabview:javaPreCompileDebug最新任务:tabview:compileDebugKotlin最新日期任务:tabview:compileDebugJavaWithJavac UP- Task任务:tabview:bundleLibCompileToJarDebug UP-TO-DATE Task :app:compileDebugKotlin UP-TO DATE Task :app:javaPreCompileDebug -TO-DATE Task :app:compileDebugJavaWithJavac TO DATE Task :app:compileDebugSources Task :app:mergeDebugShaders app:mergeDebugShaders DATE任务：选项卡视图:mergeDebugShaders最新任务:tabview:编译器mergeDebugShaders无源任务:tabview:generateDebugAssets任务:tabview:packageDebugAssets UP-TO任务:app:mergeDebugAssets TO任务:app:processDebugJavaRes NO-SOURCE Task :tabview:processDebugJavaRes NO-SOURCE Task :tabview:bundleLibResDebug UP-TO-DATE Task :app:mergeDebugJavaResource UP-TO DATE:DATE:bundleLibRuntimeToJarDebug UP-DATE- Task :tabview:dexBuilderDebug app:DATE:tabview:DATE:DATE任务-DATE任务:应用程序:mergeDexDebug最新任务:app:mergeDebugJniLibFolders最新任务:tabview:mergeDebugJniLibFolders最新任务:tabview:mergeDebugNativeLibs 在829 to中成功构建40个可操作的任务:40个最新的BUILD Analyzer结果可用

但是，当我将这个片段切换为active (带有片段的tabView)时，它会给出：

不幸的是，应用程序已经停止

在从AppCompatActivity()转换时，我会错过什么？

以前：

package com.myPackage.application
import android.annotation.SuppressLint
import android.app.PendingIntent.getActivity
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.ImageView
import android.widget.TextView
import androidx.core.content.ContextCompat
import androidx.core.content.res.ResourcesCompat
import kotlinx.android.synthetic.main.activity_start_carousel.*

class StartCarouselActivity : AppCompatActivity() {

    private val movies = arrayListOf(R.drawable.ic_action_tab1, R.drawable.ic_action_tab2, R.drawable.ic_action_tab3)
    private val moviesTitles = arrayListOf("Harry Potter", "Konosuba", "I Am Legend")
    private val trending = arrayListOf(R.drawable.ic_action_tab1, R.drawable.ic_action_tab2, R.drawable.ic_action_tab3)

    private val trendingTitles = arrayListOf("Lord of the Rings", "The Last Naruto the Movie", "Spirited Away")

    @SuppressLint("UseCompatLoadingForDrawables")
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_start_carousel)

        carouselView1.apply {
            size = movies.size
            resource = R.layout.start_carousel_movies_item
            scaleOnScroll = true
            spacing = 50
            hideIndicator(true)
            setCarouselViewListener { view, position ->
                val imageView = view.findViewById<ImageView>(R.id.imageView)
                imageView.setImageDrawable(ResourcesCompat.getDrawable(resources, movies[position], null))
                val textView = view.findViewById<TextView>(R.id.textViewTitle)
                textView.text = moviesTitles[position]
            }
            show()
        }

        carouselView2.apply {
            val trendingMovies = trending + movies
            val trendingTitle = trendingTitles + moviesTitles

            size = trendingMovies.size
            resource = R.layout.start_carousel_trending_item
            spacing = 50
            hideIndicator(true)
            setCarouselViewListener { view, position ->
                val imageView = view.findViewById<ImageView>(R.id.imageView)
                imageView.setImageDrawable(ResourcesCompat.getDrawable(resources, trendingMovies[position], null))
                val textView = view.findViewById<TextView>(R.id.textViewTitle)
                textView.text = trendingTitle[position]
            }
            show()
        }

    }
}

后：

package com.myPackage.application
import android.annotation.SuppressLint
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import android.widget.TextView
import androidx.core.content.res.ResourcesCompat
import androidx.fragment.app.Fragment
import kotlinx.android.synthetic.main.activity_start_carousel.*
import kotlinx.android.synthetic.main.fragment_tab2.view.*

class TabFragment2 : Fragment() {
    private val movies = arrayListOf(
        R.drawable.ic_action_tab1,
        R.drawable.ic_action_tab2,
        R.drawable.ic_action_tab3
    )
    private val moviesTitles = arrayListOf("Harry Potter", "Konosuba", "I Am Legend")
    private val trending = arrayListOf(
        R.drawable.ic_action_tab1,
        R.drawable.ic_action_tab2,
        R.drawable.ic_action_tab3
    )

    private val trendingTitles = arrayListOf(
        "Lord of the Rings",
        "The Last Naruto the Movie",
        "Spirited Away"
    )

    @SuppressLint("UseCompatLoadingForDrawables")
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        super.onCreate(savedInstanceState)
        val v: View = inflater.inflate(R.layout.activity_start_carousel, container, false)

        carouselView1.apply {
            size = movies.size
            resource = R.layout.start_carousel_movies_item
            scaleOnScroll = true
            spacing = 50
            hideIndicator(true)
            setCarouselViewListener { view, position ->
                val imageView = view.findViewById<ImageView>(R.id.imageView)
                imageView.setImageDrawable(
                    ResourcesCompat.getDrawable(
                        resources,
                        movies[position],
                        null
                    )
                )
                val textView = view.findViewById<TextView>(R.id.textViewTitle)
                textView.text = moviesTitles[position]
            }
            show()
        }

        carouselView2.apply {
            val trendingMovies = trending + movies
            val trendingTitle = trendingTitles + moviesTitles

            size = trendingMovies.size
            resource = R.layout.start_carousel_trending_item
            spacing = 50
            hideIndicator(true)
            setCarouselViewListener { view, position ->
                val imageView = view.findViewById<ImageView>(R.id.imageView)
                imageView.setImageDrawable(
                    ResourcesCompat.getDrawable(
                        resources,
                        trendingMovies[position],
                        null
                    )
                )
                val textView = view.findViewById<TextView>(R.id.textViewTitle)
                textView.text = trendingTitle[position]
            }
            show()
        }
        return  v
    }
}

Answer 1

假设您的旋转木马视图ID是carouselView1和carouselView2，则应该使用

v.findViewById<CarouselView>(R.id.carouselView1).apply { ... }

和

v.findViewById<CarouselView>(R.id.carouselView2).apply { ... }

在onCreateView中实例化您的旋转木马视图。

kotlin中的应用函数是一个范围函数，它引用上下文对象(在本例中是两个CarouselView)并返回它。

因此，在您的示例中，v.findViewById<CarouselView>(R.id.carouselView1).apply { ... }和v.findViewById<CarouselView>(R.id.carouselView2).apply { ... }都返回一个CarouselView。

如果您需要在Fragment中全局使用您的视图，则此行为可能很有用。

    private var carouselView1: CarouselView? = null

    @SuppressLint("UseCompatLoadingForDrawables")
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        super.onCreate(savedInstanceState)
        val v: View = inflater.inflate(R.layout.activity_start_carousel, container, false)

        carouselView1 = v.findViewById<CarouselView>(R.id.carouselView1).apply { ... }
    }

    fun exampleFunction() {
        // Example operation to explain the global use of this variable
        carouselView1?.spacing = 10
    }

有关Kotlin的作用域函数的更多信息，请参见这里。

但是，片段代码的主要问题是没有在充气视图(v)中搜索您的v。实际上，在您的AppCompactActivity中，您不需要在findViewById之前引用特定的视图，因为onCreate中的setContentView方法会自动膨胀布局。

这就是代码语法v.findViewById<ViewType>(<view-id>)的原因。