使用OkHttp快取時空物件上的Context.getApplicationContext()'

我正在嘗試使用 oKhttp 從 API 快取我的資料并將這些資料保存到 FILE 中。問題是當我嘗試applicationContext.cacheDir在我的NetworkLayer類中使用 , 但它給了我一個錯誤。

• 我試圖讓我的NetworkLayer從Application()擴展，但問題仍然存在。

• 我也試圖對這個問題進行一些搜索，但我沒有找到任何相關的東西。提前致謝。

這是我的代碼

網路層

class NetworkLayer : Application() {

private val BASE_URL = ""
private val moshi: Moshi = Moshi.Builder().addLast(KotlinJsonAdapterFactory()).build()

private fun myHttpClient(): OkHttpClient {
    val interceptor = HttpLoggingInterceptor()
    interceptor.level = HttpLoggingInterceptor.Level.BODY

    val httpCacheDirectory = File(applicationContext.cacheDir, "http-cache")
    val cacheSize = 10 * 1024 * 1024 // 10 MiB
    val cache = Cache(httpCacheDirectory, cacheSize.toLong())

    val builder = OkHttpClient()
        .newBuilder()
        .addNetworkInterceptor(CacheInterceptor())
        .cache(cache)
        .addInterceptor(interceptor)
        .callTimeout(3, TimeUnit.SECONDS)
        .connectTimeout(3, TimeUnit.SECONDS)
    return builder.build()
}

private val retrofit: Retrofit = Retrofit.Builder()
    .baseUrl(BASE_URL)
    .client(myHttpClient())
    .addConverterFactory(MoshiConverterFactory.create(moshi))
    .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
    .build()

val apiService: APIService by lazy {
    retrofit.create(APIService::class.java)
   }
}

問題就在這里，在這個代碼行

• val httpCacheDirectory = File(applicationContext.cacheDir, "http-cache")

我的CacheInterceptor類

class CacheInterceptor : Interceptor {
override fun intercept(chain: Interceptor.Chain): Response {
    val response: Response = chain.proceed(chain.request())
    val cacheControl = CacheControl.Builder()
        .maxAge(1, TimeUnit.DAYS)
        .build()
    return response.newBuilder()
        .removeHeader("Pragma")
        .removeHeader("Cache-Control")
        .header("Cache-Control", cacheControl.toString())
        .build()
    }
}

錯誤訊息_

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.moataz.afternoonhadeeth/com.moataz.afternoonhadeeth.ui.view.activity.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3430)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3614)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:86)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2199)
    at android.os.Handler.dispatchMessage(Handler.java:112)
    at android.os.Looper.loop(Looper.java:216)
    at android.app.ActivityThread.main(ActivityThread.java:7625)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:524)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:987)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
    at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:116)
    at com.moataz.afternoonhadeeth.data.request.NetworkLayer.myHttpClient(NetworkLayer.kt:26)
    at com.moataz.afternoonhadeeth.data.request.NetworkLayer.<init>(NetworkLayer.kt:42)
    at com.moataz.afternoonhadeeth.data.repository.ApiClient.<init>(ApiClient.kt:12)
    at com.moataz.afternoonhadeeth.ui.viewmodel.HomeViewModel.<init>(HomeViewModel.kt:16)
    at com.moataz.afternoonhadeeth.ui.view.fragment.HomeFragment.<init>(HomeFragment.kt:25)
    at com.moataz.afternoonhadeeth.ui.view.activity.MainActivity.initializeBottomNavigation(MainActivity.kt:71)
    at com.moataz.afternoonhadeeth.ui.view.activity.MainActivity.onCreate(MainActivity.kt:46)
    at android.app.Activity.performCreate(Activity.java:7458)
    at android.app.Activity.performCreate(Activity.java:7448)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1286)

編輯：這是最終代碼

class NetworkLayer : AppCompatActivity() {

private val BASE_URL = ""
private val moshi: Moshi = Moshi.Builder().addLast(KotlinJsonAdapterFactory()).build()
private val myHttpClient = OkHttpClient()

override fun onCreate(savedInstanceState: Bundle?, persistentState: PersistableBundle?) {
    super.onCreate(savedInstanceState, persistentState)
    val interceptor = HttpLoggingInterceptor()
    interceptor.level = HttpLoggingInterceptor.Level.BODY

    val httpCacheDirectory = File(applicationContext.cacheDir, "http-cache")
    val cacheSize = 10 * 1024 * 1024 // 10 MiB
    val cache = Cache(httpCacheDirectory, cacheSize.toLong())

    myHttpClient
        .newBuilder()
        .addNetworkInterceptor(CacheInterceptor())
        .addInterceptor(ForceCacheInterceptor())
        .cache(cache)
        .callTimeout(3, TimeUnit.SECONDS)
        .connectTimeout(3, TimeUnit.SECONDS)
        .build()
}

private val retrofit: Retrofit = Retrofit.Builder()
    .baseUrl(BASE_URL)
    .client(myHttpClient)
    .addConverterFactory(MoshiConverterFactory.create(moshi))
    .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
    .build()

val apiService: APIService by lazy {
    retrofit.create(APIService::class.java)
    }
}

uj5u.com熱心網友回復：

applicationContext.cacheDir必須在課后 打電話。onCreate()Application

在您的代碼myHttpClient()中呼叫之前 也是onCreate()如此。applicationContextnull

要解決此問題，您可以retrofit在應用程式中創建onCreate()

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