ListView RuntimeException

Question

我已经创建了一个应用程序，用于在登录后获取联系人列表，但是登录后该应用程序停止运行，而不是打开ContactActivity.java 这是我的LOGCAT和ContactActivity代码。请有人帮忙...

我试图解决问题，但没有成功

LOGCAT：

W/art: Before Android 4.1, method int android.support.v7.widget.ListViewCompat.lookForSelectablePosition(int, boolean) would have incorrectly overridden the package-private method in android.widget.ListView
V/BoostFramework: BoostFramework() : mPerf = com.qualcomm.qti.Performance@45289e1
I/Timeline: Timeline: Activity_launch_request time:145293352 intent:Intent { cmp=com.delaroystudios.sqlitelogin/com.delaroystudios.filterContacts.activities.ContactActivity }
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.delaroystudios.sqlitelogin, PID: 26883
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.delaroystudios.sqlitelogin/com.delaroystudios.filterContacts.activities.ContactActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2625)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2784)
        at android.app.ActivityThread.-wrap12(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1523)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:163)
        at android.app.ActivityThread.main(ActivityThread.java:6238)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:933)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:823)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
        at android.app.Activity.findViewById(Activity.java:2401)
        at com.delaroystudios.filterContacts.activities.ContactActivity.<init>(ContactActivity.java:26)
        at java.lang.Class.newInstance(Native Method)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1079)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2615)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2784) 
        at android.app.ActivityThread.-wrap12(ActivityThread.java) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1523) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:163) 
        at android.app.ActivityThread.main(ActivityThread.java:6238) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:933) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:823) 
I/Process: Sending signal. PID: 26883 SIG: 9
Application terminated.

contact_list_view.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorPrimaryDark">

<ListView
    android:id="@+id/list"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

</ListView>

</LinearLayout>

ContactActivity.java

package com.delaroystudios.filterContacts.activities;

import android.app.ListActivity;
import android.content.ContentResolver;
import android.database.Cursor;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
import android.widget.TextView;

import android.provider.ContactsContract;
import android.widget.Toast;

import com.delaroystudios.sqlitelogin.R;

import java.util.ArrayList;

public class ContactActivity extends ListActivity {

    ListView lv = (ListView) findViewById(R.id.list);
    Cursor cursor;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.contact_list_view);


        cursor = getContentResolver().query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI,null,null,null,null);
        startManagingCursor(cursor);

        String[] from = {ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME,ContactsContract.CommonDataKinds.Phone.NUMBER, ContactsContract.CommonDataKinds.Phone._ID};
                int[] to = {android.R.id.text1, android.R.id.text2};

        SimpleCursorAdapter listAdapter = new SimpleCursorAdapter(this,android.R.layout.simple_expandable_list_item_2,cursor,from,to);
        setListAdapter(listAdapter);

        lv = getListView();
        lv.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE);

    }

    @Override
    public long getSelectedItemId() {
        return super.getSelectedItemId();
    }

    @Override
    public int getSelectedItemPosition() {
        return super.getSelectedItemPosition();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        return super.onCreateOptionsMenu(menu);
    }
}