1.Android数据库笔记

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本人愚钝，想写一个大学课程表，之前在数据库方面各种不懂，近来再仔细观摩例程，竟然有些小小收获，特以学习笔记形式记录，方便日后复习，兼作备份代码之用，程序不合理之处敬请拍砖，

DbHelper 继承 SQLiteOpenHelper
注意：
1.SQLiteDatabase.query的用法之一
public Cursor query (String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy)
当只查询部分行，通过 String[] columns 参数可选择
亦可通过selection，selectionArgs联合SQlite语句筛选
selection中占位符？要与selectionArgs中一一对应；
2.要掌握数据库，还需深入学习SQLite；

3.数据库中键值对插入行，修改行；

package com.example.helper;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DbHelper extends SQLiteOpenHelper {
private static final String table="course";
private static final String DbName= "Mycourse";
public DbHelper(Context context) {
super(context,DbName, null, 1);
// TODO Auto-generated constructor stub
}
public Cursor select(int weekday)
{
SQLiteDatabase db=this.getReadableDatabase();
int value[]={1,2,3,4,5,6,7,8};
String tochar[] = {"1","2","3","4","5","6","7","8"};
//for (int i=0;i<8;i++) value[i]+=weekday*8;
//for (int i=0;i<8;i++) tochar[i]=Integer.toString(value[i]);
//String[] wherevalue={tochar[0],tochar[1],tochar[2],tochar[3],tochar[4],tochar[5],tochar[6],tochar[7]};
String[] wherevalue={"12","0"};
Cursor cursor=db.query("course", null,"_id<? and _id>?",wherevalue, null, null,null);
return cursor;
}
public long insert(CourseData data)
{
SQLiteDatabase db=this.getReadableDatabase();
ContentValues cv=new ContentValues();
cv.put("name",data.getName());
cv.put("time",data.getTime());
long rowid=db.insert(table, null, cv);
return rowid;
}
public void delete(CourseData data,int id)
{
SQLiteDatabase db=this.getReadableDatabase();
String where="_id=?";
String[] wherevalue={Integer.toString(id)};
db.delete(table, where, wherevalue);
}
public void upgrade(CourseData data,int id)
{
SQLiteDatabase db=this.getReadableDatabase();
ContentValues cv=new ContentValues();
String where="_id=?";
String[] wherevalue={Integer.toString(id)};
cv.put("name",data.getName());
cv.put("time",data.getTime());
db.update(table,cv, where, wherevalue);
}
public void initial()
{
SQLiteDatabase db=this.getReadableDatabase();
CourseData emptydata=new CourseData();
for(int i=0;i<10;i++)
{
emptydata.setName(String.valueOf(i));
emptydata.setTime(i);
insert(emptydata);
}
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL("create table course(_id integer primary key autoincrement,name varchar[20],time integer);");
}
@Override
public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
// TODO Auto-generated method stub
}
}

Activity类：

注意：

1.ListView 通过invalidateViews重画(貌似必须在主线程里)

2.抛出异常

import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteCursor;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
import com.example.helper.CourseData;
import com.example.helper.DbHelper;
public class MainActivity extends Activity {
private static final String TAG = "MainActivity";
private Button bn1;
private Button bn2;
private Button bn3;
private ListView lv;
private Cursor cursor;
private SimpleCursorAdapter scAdapter;
private DbHelper myDbHelper;
private int _id;
private EditText et1,et2;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
lv=(ListView)findViewById(R.id.lv);
myDbHelper=new DbHelper(this);
myDbHelper.initial();
cursor=myDbHelper.select(0);
bn1=(Button)findViewById(R.id.bn1);
bn2=(Button)findViewById(R.id.bn2);
bn3=(Button)findViewById(R.id.bn3);
et1=(EditText)findViewById(R.id.etname);
et2=(EditText)findViewById(R.id.ettime);
scAdapter=new SimpleCursorAdapter
(this, R.layout.listview, cursor, new String[]{"name","time"}, new int[]{R.id.CourseName,R.id.CourseTime});
lv.setAdapter(scAdapter);
Log.i(TAG, "Adapter OK");
lv.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
long arg3) {
// TODO Auto-generated method stub
Log.i(TAG, "CLICK1");
cursor.moveToPosition(arg2);
Log.i(TAG, "CLICK2");
_id=cursor.getInt(0);
Log.i(TAG, "CLICK3");
et1.setText(cursor.getString(1));
Log.i(TAG, "CLICK4");
et2.setText(String.valueOf(cursor.getInt(2)));
Log.i(TAG, cursor.getString(0));
}
});
lv.setOnItemSelectedListener(new OnItemSelectedListener() {
public void onItemSelected(AdapterView<?> arg0, View arg1,
int arg2, long arg3) {
// TODO Auto-generated method stub
SQLiteCursor sc=(SQLiteCursor)arg0.getSelectedItem();
_id=sc.getInt(0);
et1.setText(cursor.getString(1));
et2.setText(String.valueOf(cursor.getInt(2)));
Log.i(TAG, sc.getString(0));
}
public void onNothingSelected(AdapterView<?> arg0) {
// TODO Auto-generated method stub
}
});
bn1.setOnClickListener(new OnClickListener() {
public void onClick(View arg0) {
// TODO Auto-generated method stub
Log.i(TAG, "BN1 OK");
String name;
int time;
try
{
name=et1.getText().toString();
time=Integer.parseInt(et2.getText().toString());
}
catch (Exception e)
{
return;
}
Log.i(TAG, "ADD?");
add(name, time);
Log.i(TAG, "BN1 FINISH");
}
});
bn2.setOnClickListener(new OnClickListener() {
public void onClick(View arg0) {
Log.i(TAG, "BN2 OK");
// TODO Auto-generated method stub
String name;
int time;
try
{
name=et1.getText().toString();
time=Integer.parseInt(et2.getText().toString());
}
catch (Exception e)
{
return;
}
edit(name, time);
Log.i(TAG, "BN2 FINISH");
}
});
bn3.setOnClickListener(new OnClickListener() {
public void onClick(View arg0) {
Log.i(TAG, "BN3 OK");
// TODO Auto-generated method stub
String name;
int time;
try
{
name=et1.getText().toString();
time=Integer.parseInt(et2.getText().toString());
}
catch (Exception e)
{
return;
}
delete(name, time);
Log.i(TAG, "BN3 FINISH");
}
});
}
private void add(String name,int time)
{
if (name=="") return;
CourseData data=new CourseData();
data.setName(name);
data.setTime(time);
myDbHelper.insert(data);
cursor.requery();
lv.invalidateViews();
et1.setText("");
et2.setText("");
_id=0;
}
private void edit(String name,int time)
{
if (name=="") return;
CourseData data=new CourseData();
data.setName(name);
data.setTime(time);
myDbHelper.upgrade(data,_id);
cursor.requery();
lv.invalidateViews();
et1.setText("");
et2.setText("");
_id=0;
}
private void delete(String name,int time)
{
if (name=="") return;
CourseData data=new CourseData();
data.setName(name);
data.setTime(time);
myDbHelper.delete(data,_id);
cursor.requery();
lv.invalidateViews();
et1.setText("");
et2.setText("");
_id=0;
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}

最终运行效果如下：