安卓，SQLite，执行插入，查询操作，listview无结果显示，怎么解决？

Content_main.xml:
<?xml version="1.0" encoding="utf-8"?>

xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:showIn="@layout/activity_main" tools:context=".MainActivity"
android:orientation="vertical">

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/insert"
    android:text="按下这里执行和查询操作"/>
<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/textview"/>

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

android:layout_width="match_parent" android:layout_height="match_parent"
android:orientation="horizontal">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/tx1listview"/>

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/tx2listview"/>

String create="create table mytest (id varchar(255)," +
        "number varchar(255))";
Helper(Context context,String name,int version)
{
    super(context,name,null,version);
}
@Override
public void onCreate(SQLiteDatabase db)
{
    db.execSQL(create);
}
@Override
public  void onUpgrade(SQLiteDatabase db,int oldVersion,int newVersion)
{

}

}

MainActivity:
package com.example.dell_pc.sqlitetest;

import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;
import android.widget.CursorAdapter;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

Button but;
TextView tx;
SQLiteOpenHelper openHelper;
SQLiteDatabase database;
ListView listview;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });

    but=(Button)super.findViewById(R.id.insert);
    tx=(TextView)super.findViewById(R.id.textview);
    openHelper=new Helper(this,"mytesthelper.db3",1);
    listview=(ListView)super.findViewById(R.id.listview);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

public void onClick(View  v)
{
    database=openHelper.getReadableDatabase();
    database.execSQL("insert into mytest (id,number) values ('test1',1)");
    database.execSQL("insert into mytest(id,number) values('test2',2)");
    Cursor cursor=database.rawQuery("select * from mytest where id='test1'",null);
    SimpleCursorAdapter s=new SimpleCursorAdapter(this,R.layout.listview,cursor,new String[]{"id","number"},new int[]{R.id.tx1listview,R.id.tx2listview}, CursorAdapter.FLAG_REGISTER_CONTENT_OBSERVER);
    listview.setAdapter(s);
}

}
按下按钮执行插入和查询操作，listview无结果显示，请问怎么解决？