Jetpack Compose创建ViewModel时出现ClassCastException异常求助

异常信息 #

FATAL EXCEPTION: main
Process: com.github.profit, PID: 23095
java.lang.ClassCastException: java.lang.Object cannot be cast to androidx.lifecycle.ViewModel
at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.kt:201)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.kt:322)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.kt:304)
at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.kt:175)
at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.kt:138)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:187)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:153)
at androidx.lifecycle.viewmodel.compose.ViewModelKt.get(ViewModel.kt:215)
at androidx.lifecycle.viewmodel.compose.ViewModelKt.viewModel(ViewModel.kt:156)
at com.github.profit.MainActivityKt.ProductInfo(MainActivity.kt:136)
...

相关代码与配置 #

MainActivity #

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            ProfitTheme {
                Surface(
                    modifier = Modifier.fillMaxSize(),
                    color = MaterialTheme.colors.background
                ) {
                    ProductInfo()
                }
            }
        }
    }
}

ProductInfo #

@Composable
fun ProductInfo() {
    val viewModel: ProductsViewModel by viewModel()

    Column {
        TextField(
            value = viewModel.product1Price,
            onValueChange = {
                viewModel.product1Price = it
            },
            keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Number),
            label = { Text(text = "Price") },
            placeholder = { Text(text = "Price in Ft") },
        )
        // ...
    }
}

ProductsViewModel #

class ProductsViewModel: ViewModel() {
    private val _product1Price = mutableStateOf(0U)
    private val _product1Quantity = mutableStateOf(0U)
    private val _product2Price = mutableStateOf(0U)
    private val _product2Quantity = mutableStateOf(0U)

    var product1Price: String
        get() = _product1Price.value.toString()
        set(value) = setField(_product1Price, value)

    // ...
}

项目build.gradle #

buildscript {
    ext {
        compose_ui_version = '1.1.1'
        lifecycle_version = '2.5.1'
    }
}
plugins {
    id 'com.android.application' version '7.3.1' apply false
    id 'com.android.library' version '7.3.1' apply false
    id 'org.jetbrains.kotlin.android' version '1.6.10' apply false
}

应用模块build.gradle #

plugins {
    id 'com.android.application'
    id 'org.jetbrains.kotlin.android'
}

android {
    namespace 'com.github.profit'
    compileSdk 32

    defaultConfig {
        applicationId "com.github.profit"
        minSdk 22
        targetSdk 32
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        vectorDrawables {
            useSupportLibrary true
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = '1.8'
    }
    buildFeatures {
        compose true
    }
    composeOptions {
        kotlinCompilerExtensionVersion '1.1.1'
    }
    packagingOptions {
        resources {
            excludes += '/META-INF/{AL2.0,LGPL2.1}'
        }
    }
}

dependencies {
    implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$lifecycle_version"
    implementation "androidx.lifecycle:lifecycle-viewmodel-compose:$lifecycle_version"
    implementation "androidx.lifecycle:lifecycle-runtime-ktx:$lifecycle_version"

    implementation 'androidx.core:core-ktx:1.7.0'
    implementation 'androidx.activity:activity-compose:1.3.1'
    implementation "androidx.compose.ui:ui:$compose_ui_version"
    implementation "androidx.compose.ui:ui-tooling-preview:$compose_ui_version"
    implementation 'androidx.compose.material:material:1.1.1'
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.4'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.5.0'
    androidTestImplementation "androidx.compose.ui:ui-test-junit4:$compose_ui_version"
    debugImplementation "androidx.compose.ui:ui-tooling:$compose_ui_version"
    debugImplementation "androidx.compose.ui:ui-test-manifest:$compose_ui_version"
}

问题原因分析 #

该异常是因为ViewModelProvider无法正确创建ProductsViewModel实例，核心原因可能是泛型推断异常、依赖版本不兼容或项目缓存问题。

解决方案 #

1. 显式指定ViewModel泛型参数 #

修改ProductInfo中的viewModel获取代码，显式声明泛型类型，避免Kotlin泛型擦除导致的推断错误：

@Composable
fun ProductInfo() {
    val viewModel: ProductsViewModel by viewModel<ProductsViewModel>()

    Column {
        // ... 原有代码
    }
}

2. 升级依赖版本确保兼容性 #

当前使用的Compose 1.1.1与Lifecycle 2.5.1虽理论兼容，但升级到更稳定的匹配版本可避免潜在冲突：

• 修改项目根目录build.gradle：

buildscript {
    ext {
        compose_ui_version = '1.2.1'
        lifecycle_version = '2.6.1'
        kotlin_version = '1.7.10'
    }
}
plugins {
    id 'com.android.application' version '7.4.2' apply false
    id 'com.android.library' version '7.4.2' apply false
    id 'org.jetbrains.kotlin.android' version "${kotlin_version}" apply false
}

• 修改模块build.gradle中的composeOptions：

composeOptions {
    kotlinCompilerExtensionVersion '1.2.1'
}

• 同步项目依赖。

3. 验证ViewModel类的正确性 #

确认ProductsViewModel正确导入androidx.lifecycle.ViewModel，且构造函数为public（Kotlin默认即为public）：

import androidx.lifecycle.ViewModel

class ProductsViewModel: ViewModel() {
    // ... 原有代码
}

4. 清理缓存并重建项目 #

• 执行File -> Invalidate Caches... -> Invalidate and Restart
• 执行Build -> Clean Project
• 执行Build -> Rebuild Project

内容的提问来源于stack exchange，提问作者gojoGS