Android类型转换异常：Application无法转为InventoryApplication排查求助

异常日志 #

2022-12-11 02:50:28.862 24393-24393/com.example.skillit E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.skillit, PID: 24393
    java.lang.ClassCastException: android.app.Application cannot be cast to com.example.skillit.data.InventoryApplication
        at com.example.skillit.ProfileActivity$viewModel$2.invoke(ProfileActivity.kt:22)
        at com.example.skillit.ProfileActivity$viewModel$2.invoke(ProfileActivity.kt:21)
        at androidx.lifecycle.ViewModelLazy.getValue(ViewModelLazy.kt:47)
        at androidx.lifecycle.ViewModelLazy.getValue(ViewModelLazy.kt:35)
        at com.example.skillit.ProfileActivity.getViewModel(ProfileActivity.kt:21)
        at com.example.skillit.ProfileActivity.onCreate$lambda$3(ProfileActivity.kt:51)
        at com.example.skillit.ProfileActivity.$r8$lambda$733-BBVTFBdHTXlcl6xFIzJMP3c(Unknown Source:0)
        at com.example.skillit.ProfileActivity$$ExternalSyntheticLambda3.onClick(Unknown Source:2)
        at android.view.View.performClick(View.java:7881)
        at android.widget.TextView.performClick(TextView.java:16201)
        at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1219)
        at android.view.View.performClickInternal(View.java:7858)
        at android.view.View.-$$Nest$mperformClickInternal(Unknown Source:0)
        at android.view.View$PerformClick.run(View.java:30863)
        at android.os.Handler.handleCallback(Handler.java:942)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loopOnce(Looper.java:226)
        at android.os.Looper.loop(Looper.java:313)
        at android.app.ActivityThread.main(ActivityThread.java:8741)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:571)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1067)

相关代码 #

ProfileActivity.kt #

package com.example.skillit

import android.content.Intent
import android.os.Bundle
import android.view.LayoutInflater
import android.widget.Button
import android.widget.ImageView
import androidx.activity.viewModels
import androidx.appcompat.app.AppCompatActivity
import androidx.cardview.widget.CardView
import androidx.fragment.app.activityViewModels
import com.example.skillit.data.InventoryApplication
import com.example.skillit.databinding.FragmentItemDetailBinding
import com.example.skillit.databinding.ProfileActivityBinding

class ProfileActivity : AppCompatActivity() {

    //private var _binding: ProfileActivityBinding? = null
    //private val binding get() = _binding!!

    private val viewModel: InventoryViewModel by viewModels {
        InventoryViewModelFactory((application as InventoryApplication).database.itemDao())
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        this.supportActionBar?.hide()
        //_binding = ProfileActivityBinding.inflate(LayoutInflater.from(this))
        //setContentView(binding.root)
        setContentView(R.layout.profile_activity)
        val explore_button = findViewById(R.id.explore_button) as CardView
        val profile_button = findViewById(R.id.profile_button) as CardView
        val home_button = findViewById(R.id.home_button) as CardView
        val upload_button = findViewById<Button>(R.id.upload)
        home_button.setOnClickListener{
            intent = Intent(this, HomeActivity::class.java)
            startActivity(intent)
            overridePendingTransition(R.anim.slide_in_left, R.anim.slide_out_right)
        }
        explore_button.setOnClickListener{
            intent = Intent(this, ExploreActivity::class.java)
            startActivity(intent)
            overridePendingTransition(R.anim.slide_in_left, R.anim.slide_out_right)
        }
        profile_button.setOnClickListener{
            intent = Intent(this, ProfileActivity::class.java)
            startActivity(intent)
        }

        upload_button.setOnClickListener{
            viewModel.addNewItem("name", "link")
        }

    }
}

InventoryApplication.kt #

package com.example.skillit.data


import android.app.Application


class InventoryApplication : Application() {
    val database: ItemRoomDatabase by lazy { ItemRoomDatabase.getDatabase(this) }
}

ItemRoomDatabase.kt #

package com.example.skillit.data


import android.content.Context
import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase

@Database(entities = [Item::class], version = 1, exportSchema = false)
abstract class ItemRoomDatabase : RoomDatabase() {

    abstract fun itemDao(): ItemDao

    companion object {
        @Volatile
        private var INSTANCE: ItemRoomDatabase? = null

        fun getDatabase(context: Context): ItemRoomDatabase {
            // if the INSTANCE is not null, then return it,
            // if it is, then create the database
            return INSTANCE ?: synchronized(this) {
                val instance = Room.databaseBuilder(
                    context.applicationContext,
                    ItemRoomDatabase::class.java,
                    "item_database"
                )
                    // Wipes and rebuilds instead of migrating if no Migration object.
                    // Migration is not part of this codelab.
                    .fallbackToDestructiveMigration()
                    .build()
                INSTANCE = instance
                // return instance
                instance
            }
        }
    }
}

问题原因 #

核心原因是未在AndroidManifest.xml中声明自定义的InventoryApplication作为应用的Application子类，系统默认创建的是android.app.Application实例，而非你自定义的子类，导致强制类型转换失败。

解决方案 #

1. 打开项目中的AndroidManifest.xml文件
2. 在<application>标签中添加android:name属性，指定自定义Application类的全路径：

<application
    android:name="com.example.skillit.data.InventoryApplication"
    <!-- 保留原有属性，如icon、theme等 -->
    ...>
    <!-- 活动、服务等其他声明 -->
</application>

3. 清理项目缓存，重新构建并运行应用，即可解决该类型转换异常。

内容的提问来源于stack exchange，提问作者Fortnite