无法将图像分配给 Nullable ImageView

Question

如何将图像设置为 ImageView？

我的应用程序的想法是根据 RecyclerView 中的数据类显示不同类型的 RecyclerView 的视图持有者。数据类如下所示：

abstract class Thing(open val title: String, open val body: String, open val pic: ImageView?)

data class Movie(override val title: String, override val body: String): Thing(title, body, pic = null)
data class Book(override val title: String, override val body: String): Thing(title, body, pic = null)
data class Game(override val title: String, override val body: String, override val pic: ImageView?): Thing(title, body, pic)

另外，我有一个 MainFragment，我在其中手动添加数据。在这里，我试图给出游戏的名称和描述，并将特定图像设置为 game_pic ImageView：

class MainFragment: Fragment() {
private val mMoviesBooksGames = listOf(
  Game("Dixit", "Give the perfect clue so most (not all) players guess the right surreal image card.", game_pic.setImageResource(R.drawable.alias) as ImageView)
  }
}

我如何声明 game_pic 所在的 GameViewHolder：

class GameViewHolder(inflater: LayoutInflater, parent: ViewGroup) :
    ThingViewHolder(inflater.inflate(R.layout.game_list_item, parent, false)) {
    private var mGameTitleView: TextView? = null
    private var mGameDescriptionView: TextView? = null
    private var mGamePicImageView: ImageView? = null

    init {
        mGameTitleView = itemView.findViewById(R.id.game_title)
        mGameDescriptionView = itemView.findViewById(R.id.game_description)
        mGamePicImageView = itemView.findViewById(R.id.game_pic)
    }

    override fun bind(dataToBind: Thing) {
        mGameTitleView?.text = ">> Book ${dataToBind.title}"
        mGameDescriptionView?.text = dataToBind.body
        mGamePicImageView = dataToBind.pic
    }
}

使用game_pic.setImageResource(R.drawable.alias) as ImageView 后出现的错误是：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.recyclerview, PID: 822
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.recyclerview/com.example.recyclerview.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageResource(int)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3555)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3707)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2220)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:237)
        at android.app.ActivityThread.main(ActivityThread.java:8019)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1100)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageResource(int)' on a null object reference
        at com.example.recyclerview.MainFragment.<init>(MainFragment.kt:33)
        at com.example.recyclerview.MainFragment$Companion.newInstance(MainFragment.kt:67)
        at com.example.recyclerview.MainActivity.createFragment(MainActivity.kt:4)
        at com.example.recyclerview.MainActivity.createFragment(MainActivity.kt:3)
        at com.example.recyclerview.SingleFragmentActivity.onCreate(SingleFragmentActivity.kt:25)
        at android.app.Activity.performCreate(Activity.java:7957)
        at android.app.Activity.performCreate(Activity.java:7946)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1307)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3530)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3707) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2220) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:237) 
        at android.app.ActivityThread.main(ActivityThread.java:8019) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1100) 
I/Process: Sending signal. PID: 822 SIG: 9

Answer 1

data class Game(
    override val title: String, 
    override val body: String,
    override val image: Int)

像这样修改数据类

override fun bind(dataToBind: Thing) {
    mGameTitleView?.text = ">> Book ${dataToBind.title}"
    mGameDescriptionView?.text = dataToBind.body
    mGamePicImageViewsetImageResource(dataToBind.pic)
}

然后像这样将代码替换到您的视图持有者中

data class Game(
    "Dixit", 
    "Give the perfect clue so most (not all) players guess the right surreal image card.", 
    R.drawable.your_pic

)

然后尝试将此值放入您的游戏缺点中。

Answer 2

错误表明您的 game_pic 变量为空。

我可以在不查看您的代码的情况下建议一种解决方法：

private val mMoviesBooksGames = listOf( Game(
        "Dixit", 
        "Give the perfect clue so most (not all) players guess the right surreal image card.", 
        ImageView(this).apply { setImageResource(R.drawable.alias) })
)

在非空实例上构造 ImageView 并设置图片资源。 或者你可以在某个地方初始化你的game_pic，例如onCreateView方法，然后再初始化你的mMoviesBooksGames。

UPD：

1. 您不应将您的视图声明为可为空。
2. 您可以通过其他方式设置图片资源。

首先，您在init 中初始化您的mGamePicImageView，然后在bind 中重写它。其次，您可以改为仅将可绘制数据传递给视图持有者，而不是全新的 ImageView。

我建议你重新设计你的数据类：

data class Game(
    override val title: String, 
    override val body: String,
    override val imageDrawable: Drawable)

然后在viewholder的bind方法中

mGamePicImageView.setImageDrawable(dataToBind.imageDrawable)

最后

private val mMoviesBooksGames = listOf( Game(
    "Dixit", 
    "Give the perfect clue so most (not all) players guess the right surreal image card.", 
    ContextCompat.getDrawable(this.activity, android.R.drawable.alias))
    )

getDrawable 的第一个参数不是上下文，所以将片段的父活动传递给那里。第二个参数是drawable的id，我不确定你是否需要前缀android.，所以你也可以试试R.drawable.alias。