运用数据库来存储小信息

运用数据库来存储小信息

本次的任务是

将学生信息存入数据库

显示所有学生信息列表

删除数据库表中第一条信息

就是你输入什么 手机就可以把输入的内容存储在数据库里

方便读取和删除

嗯 就这样

这个有点小麻烦 还有数据库语句什么的

还是谈正事 布局代码就不详写了 直接贴上主要的小部分

    <EditText
       android:id="@+id/et_name"
       android:layout_width="match_parent"
       android:layout_height="55dp" />
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <Button
            android:id="@+id/btn_add"
            android:layout_width="0dp"
            android:onClick="onClick"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="增加一条信息" />
        <Button
            android:id="@+id/btn_del"
            android:layout_width="0dp"
            android:onClick="onClick"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="删除一条信息" />
    </LinearLayout>
    <ListView
        android:id="@+id/list_info"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    </ListView>

easy easy

---

来贴Java代码部分

让其读取到输入的内容并且保存

然后再点读取的时候将它弄出来

嗯 还行吧

等等 还得把不想要的删除掉

---

操作数据库Java代码

    public class InfoDAO  {

    private MainDbHelper helper;
    private SQLiteDatabase db;

    public InfoDAO (Context context) {
        helper = new MainDbHelper(context);
    }
    public  void insert(String name){
        db = helper.getWritableDatabase();
        String sql = "insert into student(name) values('"+name+"')";
        db.execSQL(sql);

    }

    public Cursor selectAll() {
        db = helper.getReadableDatabase();
        Cursor cursor = db.query("student", null, null, null, null, null, null);
        return cursor;
    }

    public void delete(String id) {
        db = helper.getWritableDatabase();
        String sql = "delete from student where _id="+String.valueOf(id);
        db.execSQL(sql);
    }
    }

---

创建和打开数据库

    public class MainDbHelper extends SQLiteOpenHelper {
    private String sql = "create table student(_id integer primary key autoincrement,name txt)";

    public MainDbHelper(Context context) {
        super(context, "student", null, 1);
    }

    //当APP中没有数据库或者数据库版本为1的时候会被调用,且只调用一次
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        sqLiteDatabase.execSQL(sql);
    }


    @Override
    //升级数据库表.当newVersion > oldVersion,会被调用
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {
        sqLiteDatabase.execSQL("drop table if exists student");
        onCreate(sqLiteDatabase);

    }
    }

---

再来一个自定义的Adapter用来解析cursor类型的数据UoCursorAdapter继承自CursonAdapter类

---

    public class UoCursorAdapter extends CursorAdapter {


    public UoCursorAdapter(Context context, Cursor cursor) {
        super(context, cursor, 0);
    }

    @Override
    public View newView(Context context, Cursor cursor, ViewGroup viewGroup) {
        return LayoutInflater.from(context).inflate(R.layout.activity_info,viewGroup,false);
    }

    @Override
    public void bindView(View view, Context context, Cursor cursor) {
        TextView name = (TextView) view.findViewById(R.id.tv_name);
        name.setText(cursor.getString(cursor.getColumnIndex("name")));
    }
    }

---

最后是主类Java代码

---

    public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    private Button btn_add;
    private EditText et_name;
    InfoDAO infoDAO;
    Cursor cursor;
    UoCursorAdapter uoCursorAdapter;
    private ListView list_info;


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

        et_name = (EditText) findViewById(R.id.et_name);

        list_info = (ListView)findViewById(R.id.list_info);
        infoDAO = new InfoDAO(this);
        cursor = infoDAO.selectAll();
        if(cursor!=null) {
            uoCursorAdapter = new UoCursorAdapter(this, cursor);
            list_info.setAdapter(uoCursorAdapter);
        }
    }

    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.btn_add:
                String name = et_name.getText().toString();
                if (TextUtils.isEmpty(name)) {
                    Toast.makeText(MainActivity.this, "姓名,班级不能为空", 
                            Toast.LENGTH_SHORT).show();
                    return;
                }
                 infoDAO.insert(name);
                 cursor = infoDAO.selectAll();
                if(cursor!=null) {
                    uoCursorAdapter = new UoCursorAdapter(this, cursor);
                    list_info.setAdapter(uoCursorAdapter);
                }
                break;
            case R.id.btn_del:
                if(cursor!=null){
                    if(cursor.moveToFirst()){
                        infoDAO.delete(cursor.getString(cursor.getColumnIndex("_id")));
                        cursor = infoDAO.selectAll();
                    }
                }
                uoCursorAdapter = new UoCursorAdapter(this,cursor);
                list_info.setAdapter(uoCursorAdapter);
                break;
        }
    }

结束了

说实话 写博客 越写越简单短小 不过这篇算比较多的 因为数据库很烦啊 哈哈哈