运行 Android studio App 与 OkHTTP 使用 Kotlin 时的实例化错误

Question

使用 OkHTTP 我正在尝试检索文本文件并将帽子放入主 activity 上的 textView， Gradle 会说构建成功，但模拟器应用程序只会在启动时崩溃并提供此错误。

我在 AndroidManifest.xml 中添加了正确的权限，在 gradle build

中添加了正确的实现

package com.example.vectortestapi

import android.os.Bundle
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import okhttp3.*
import java.io.IOException


abstract class MainActivity : AppCompatActivity() {
    private val mTextView: TextView =   findViewById<TextView>(R.id.resultText);
    private val client = OkHttpClient()

    private val url = "https://publicobject.com/helloworld.txt"
    private val request: Request = Request.Builder()
            .url(url)
            .build();
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        getAPI();
    }
    private fun getAPI(){
        client.newCall(request).enqueue(object: Callback {
            override fun onFailure(call: Call, e: IOException) {
                e.printStackTrace()
            }

            override fun onResponse(call: Call, response: Response) {
                val inputStream = response.body?.string()
                runOnUiThread{
                    mTextView.text = inputStream
                }
            }

        })

    }
}

产生此错误：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.vectortestapi, PID: 9900
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.vectortestapi/com.example.vectortestapi.MainActivity}: java.lang.InstantiationException: java.lang.Class<com.example.vectortestapi.MainActivity> cannot be instantiated
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3365)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7656)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
     Caused by: java.lang.InstantiationException: java.lang.Class<com.example.vectortestapi.MainActivity> cannot be instantiated
        at java.lang.Class.newInstance(Native Method)
        at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:95)
        at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:45)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1253)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3353)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7656)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
D/libEGL: loaded /vendor/lib/egl/libGLESv2_emulation.so
I/Process: Sending signal. PID: 9900 SIG: 9

Answer 1

抽象类不能实例化，但可以子类化。

运行 Android studio App 与 OkHTTP 使用 Kotlin 时的实例化错误

Instantation Error when running Android studio App with OkHTTTP Using Kotlin

android

kotlin

android-studio

okhttp