Android Studio插座问题.无法解析libcore.util.objects

Question

我有一个Android应用，将数据发送到在Raspberry Pi上运行的CPP服务器。直到我更新Android Studio之前，它都可以正常工作，现在我遇到了此错误：Method threw 'java.lang.NullPointerException' exception. Cannot evaluate android.system.StructAddrinfo.toString()

我在Socket sock = null;(请参阅下(设置了一个断点，然后单击一步，直到到达StructAddrinfo.java(请参见下文(，这是我在上面列出的错误的地方。在此文件中，libcore.util.Objects无法解决。

我一直在尝试修复数小时，但没有运气...

client.java：

package com.senoirdesign.seniorassistant;
import android.os.AsyncTask;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;
/**
 * Created by toddf on 11/20/2017.
 */
/* class for socket stuff */
public class Client extends AsyncTask<Void, Void, Void> {
    String ip_addr;
    int port_num;
    String msg;
    /* Constructor for Client class */
    Client(String ip, int port, String message) {
        ip_addr = ip;
        port_num = port;
        msg = message;
    }
    @Override
    protected Void doInBackground(Void... args) {
        Socket sock = null;
        try {
            sock = new Socket(ip_addr, port_num);
            DataOutputStream DOS = new DataOutputStream(sock.getOutputStream());
            DOS.writeUTF(msg);
            DOS.flush();
            sock.close();
        } catch(UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
}

structaddrinfo.java：

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package android.system;
import java.net.InetAddress;
import libcore.util.Objects;
/**
 * Information returned/taken by getaddrinfo(3). Corresponds to C's {@code struct addrinfo} from
 * <a href="http://pubs.opengroup.org/onlinepubs/009695399/basedefs/netdb.h.html">&lt;netdb.h&gt;</a>
 *
 * TODO: we currently only _take_ a StructAddrinfo; getaddrinfo returns an InetAddress[].
 *
 * @hide
 */
public final class StructAddrinfo {
  /** Flags describing the kind of lookup to be done. (Such as AI_ADDRCONFIG.) */
  public int ai_flags;
  /** Desired address family for results. (Such as AF_INET6 for IPv6. AF_UNSPEC means "any".) */
  public int ai_family;
  /** Socket type. (Such as SOCK_DGRAM. 0 means "any".) */
  public int ai_socktype;
  /** Protocol. (Such as IPPROTO_IPV6 IPv6. 0 means "any".) */
  public int ai_protocol;
  /** Address length. (Not useful in Java.) */
  // public int ai_addrlen;
  /** Address. */
  public InetAddress ai_addr;
  /** Canonical name of service location (if AI_CANONNAME provided in ai_flags). */
  // public String ai_canonname;
  /** Next element in linked list. */
  public StructAddrinfo ai_next;
  @Override public String toString() {
    return Objects.toString(this);
  }
}

gradle(app(：

apply plugin: 'com.android.application'
android {
    compileSdkVersion 25
    buildToolsVersion '26.0.2'
    defaultConfig {
        applicationId "com.senoirdesign.seniorassistant"
        minSdkVersion 21
        targetSdkVersion 25
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}
dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support.constraint:constraint-layout:1.0.2'
    compile 'com.android.support:appcompat-v7:25.4.0'
    testCompile 'junit:junit:4.12'
}

gradle(项目(：

// Top-level build file where you can add configuration options common to all sub-projects/modules.
buildscript {
    repositories {
        jcenter()
        google()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.0.1'
        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}
allprojects {
    repositories {
        jcenter()
        google()
    }
}
task clean(type: Delete) {
    delete rootProject.buildDir
}

Answer 1

我解决了我的问题。经过很多事情，我遵循了这些步骤https://teamtreehouse.com/community/getting-cannot-collove-symbol-error-eror-eror-eror-after-converting-android-project-form-eceplorm-eclipse-to android-studio-with-with-with-gradle-with-gradle要更新编译SDK版本并构建项目的工具版本，然后我确实文件 ->无效CACHE＆amp;重新开始。修复了它。