安卓学习-数据存储与IO-Sqlite

public class MainActivity extends Activity implements OnClickListener{

    Button btn1;
    Button btn2;
    Button btn3;
    EditText editText1;
    EditText editText2;
    SQLiteDatabase db;
    ListView listView1;
    Cursor cursor;
    

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn1=(Button)findViewById(R.id.button1);
        btn2=(Button)findViewById(R.id.button2);
        btn3=(Button)findViewById(R.id.button3);
        btn1.setOnClickListener(this);
        btn2.setOnClickListener(this);
        btn3.setOnClickListener(this);
        
        editText1=(EditText)findViewById(R.id.editText1);
        editText2=(EditText)findViewById(R.id.editText2);
        listView1=(ListView)findViewById(R.id.listView1);
        try {
            File file= new File(getFilesDir().getCanonicalPath()+"/test.db");
    
            if(file.exists()){
                file.delete();
            }
            
            //打开数据库，不存在则创建
            db=SQLiteDatabase.openOrCreateDatabase(getFilesDir().getCanonicalPath()+"/test.db", null);
            String sql=
            "CREATE TABLE t_test ("+
            "        _id  INTEGER NOT NULL,"+
            "        name  TEXT,"+
            "        PRIMARY KEY (_id ASC)"+
            "        )";
            db.execSQL(sql);
        } catch (IOException e) {
            // TODO 自动生成的 catch 块
            e.printStackTrace();
        }
    }

    public void onClick(View paramView) {
        if(paramView==btn1){
            int _id=Integer.parseInt(editText1.getText().toString());
            String name=editText2.getText().toString();
            String sql="select * from t_test where _id="+_id;
            Cursor cursor=db.rawQuery(sql, null);
            if(cursor.getCount()>0){
                Toast.makeText(MainActivity.this, "记录已存在", Toast.LENGTH_SHORT).show();
            }else{
                sql="INSERT INTO t_test VALUES (?, ?)";
                db.execSQL(sql, new Object[]{_id,name});
            }
        }else if(paramView==btn2){
            int _id=Integer.parseInt(editText1.getText().toString());
            String name=editText2.getText().toString();
            String sql="update t_test set _id=?,name=? where _id=?";
            db.execSQL(sql, new Object[]{_id,name,_id});
        }else if(paramView==btn3){
            int _id=Integer.parseInt(editText1.getText().toString());
            String sql="delete from t_test where _id=?";
            db.execSQL(sql, new Object[]{_id});
            editText1.setText("");
            editText2.setText("");
        }
        
        cursor=db.rawQuery("select * from t_test", null);
        SimpleCursorAdapter adapter=new SimpleCursorAdapter(MainActivity.this,
                R.layout.item, cursor, new String[]{"_id","name"}, new int[]{R.id.textView2,R.id.textView4});
        listView1.setAdapter(adapter);
        listView1.setOnItemClickListener(new OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> paramAdapterView,
                    View paramView, int paramInt, long paramLong) {
                if(cursor.moveToPosition(paramInt)){
                    editText1.setText(""+cursor.getInt(cursor.getColumnIndex("_id")));
                    editText2.setText(cursor.getString(cursor.getColumnIndex("name")));
                }                
            }
        });
    }
}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" android:padding="10dp">

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="15dp"
        android:text="ID："
        android:textAppearance="?android:attr/textAppearanceMedium" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/textView1"
        android:layout_alignBottom="@+id/textView1"
        android:layout_marginLeft="33dp"
        android:layout_toRightOf="@+id/textView1"
        android:text="001"
        android:textAppearance="?android:attr/textAppearanceMedium" />

    <TextView
        android:id="@+id/textView3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/textView2"
        android:layout_alignBottom="@+id/textView2"
        android:layout_marginLeft="17dp"
        android:layout_toRightOf="@+id/textView2"
        android:text="名字："
        android:textAppearance="?android:attr/textAppearanceMedium" />

    <TextView
        android:id="@+id/textView4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/textView3"
        android:layout_alignBottom="@+id/textView3"
        android:layout_marginLeft="27dp"
        android:layout_toRightOf="@+id/textView3"
        android:text="测试1"
        android:textAppearance="?android:attr/textAppearanceMedium" />

</RelativeLayout>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="${relativePackage}.${activityClass}" >

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/button1"
        android:layout_alignBottom="@+id/button1"
        android:layout_centerHorizontal="true"
        android:text="修改" />

    <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/button2"
        android:layout_alignBottom="@+id/button2"
        android:layout_alignParentRight="true"
        android:layout_marginRight="21dp"
        android:text="删除" />

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/editText2"
        android:layout_marginTop="11dp"
        android:text="添加" />

    <EditText
        android:id="@+id/editText2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/textView2"
        android:layout_alignParentRight="true"
        android:layout_toRightOf="@+id/button1"
        android:ems="10" >

        <requestFocus />
    </EditText>

    <EditText
        android:id="@+id/editText1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/editText2"
        android:layout_alignParentRight="true"
        android:layout_alignTop="@+id/textView1"
        android:ems="10" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignRight="@+id/button1"
        android:layout_below="@+id/editText1"
        android:layout_marginTop="19dp"
        android:text="名字"
        android:textAppearance="?android:attr/textAppearanceMedium" />

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/textView2"
        android:layout_alignParentTop="true"
        android:layout_marginTop="21dp"
        android:layout_toLeftOf="@+id/editText1"
        android:text="id"
        android:textAppearance="?android:attr/textAppearanceMedium" />

    <ListView
        android:id="@+id/listView1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_below="@+id/button2" >

    </ListView>

</RelativeLayout>