尝试切换活动时应用崩溃

Question

我是一个菜鸟，我承担了一个比我的技能高得多的项目-制作一个停车辅助应用程序，该程序必须与物体保持距离并显示视频（来自RasPi），这些任务大部分已经完成，但是我可以在摄像机的活动之间切换。知道是什么问题吗？

这是主要活动的代码，其中包含按钮并显示距离（而不是整个文件）

public class MainActivity extends AppCompatActivity {

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
}

public void Park(View view) {
    Intent park = new Intent(this, SecondActivity.class);
    startActivity(park);
}

public void Park2(View view) {
    Intent park2 = new Intent(this, ThirdActivity.class);
    startActivity(park2);
}

这是清单

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.parkv1">

<uses-permission android:name="android.permission.INTERNET" />

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity"
        android:label="MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity android:name=".SecondActivity"
        android:label="park"></activity>
    <activity android:name=".ThirdActivity"
        android:label="park2"></activity>
</application>

Logcat：

2019-06-01 18:16:53.889 15450-15450/com.example.parkv1 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.parkv1, PID: 15450
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.parkv1/com.example.parkv1.SecondActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.setWebViewClient(android.webkit.WebViewClient)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6669)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.setWebViewClient(android.webkit.WebViewClient)' on a null object reference
    at com.example.parkv1.SecondActivity.onCreate(SecondActivity.java:14)
    at android.app.Activity.performCreate(Activity.java:7136)
    at android.app.Activity.performCreate(Activity.java:7127)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) 
    at android.os.Handler.dispatchMessage(Handler.java:106) 
    at android.os.Looper.loop(Looper.java:193) 
    at android.app.ActivityThread.main(ActivityThread.java:6669) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 

这是第二项活动：

package com.example.parkv1;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.webkit.WebView;
import android.webkit.WebViewClient;

public class SecondActivity extends AppCompatActivity {
    private WebView webview;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity2);
    webview.setWebViewClient(new WebViewClient());;
    webview.getSettings().setDomStorageEnabled(true);
    webview.setOverScrollMode(WebView.OVER_SCROLL_NEVER);
    webview.loadUrl("192.168.0.101:8081");
   }
}