如何正确获得sqlite连接？

Question

如果您可以检查代码并修复此代码中的错误Home.javapackage com.;import android.content.Intent;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.EditText;import android.widget.Toast;public class Home extends AppCompatActivity {    EditText username_editText;    EditText password_editText;    Button loginbtn;    Button registerbtn;    public static final String USERID = "userID";    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_home);        username_editText = (EditText)findViewById(R.id.home_userName);        password_editText = (EditText)findViewById(R.id.home_password);        loginbtn = (Button)findViewById(R.id.home_loginBtn);        registerbtn = (Button)findViewById(R.id.home_registerBtn);        final DBHandler dbHandler = new DBHandler(Home.this);        registerbtn.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Intent intent = new Intent("com.modelpaper.mad.it17121002.ProfileManagement");                startActivity(intent);        }    });    loginbtn.setOnClickListener(new View.OnClickListener() {        @Override        public void onClick(View view) {            String userName = username_editText.getText().toString();            String password = password_editText.getText().toString();           if(userName.equals("") || password.equals("")){               Toast.makeText(Home.this,"Login Unsuccessful",Toast.LENGTH_SHORT).show();           }           else{               UserProfile.Users users = dbHandler.readAllInfor(userName);               if(users == null){                   Toast.makeText(Home.this,"Invalid username or password",Toast.LENGTH_SHORT).show();               }我认为 db 类中有错误我找不到这个错误。app is crashed db not created 。请试着理解它

Answer 1

public class DatabaseHelper extends SQLiteOpenHelper {

 public static final String DATABASE_NAME = "student.db";

 public static final String TABLE_NAME = "student_table";

 public static final String COL1 = "ID";

 public static final String COL2 = "NAME";

 public static final String COL3 = "SURNAME"

 ;

 public static final String COL4 = "MARKS";

 

 public DatabaseHelper(Context context) {

  super(context, DATABASE_NAME, null, 1);

  // SQLiteDatabase db = this.getWritableDatabase(); }

 

  public void onCreate(SQLiteDatabase db) {

   db.execSQL(" create table " + TABLE_NAME + "(ID INTEGER PRIMARY KEY AUTOINCREMENT, NAME TEXT, SURNAME TEXT, MARKS INTEGER)");

  }

  @Override

  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

   db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);

   onCreate(db);

  }

  public boolean insertData(String name, String surname, String marks) {

   SQLiteDatabase db = this.getWritableDatabase();

   ContentValues contentValues = new ContentValues();

   contentValues.put(COL2, name);

   contentValues.put(COL3, surname);

   contentValues.put(COL4, marks);

   long result = db.insert(TABLE_NAME, null, contentValues);

   if (result == -1)

    return false;

   else

    return true;

  }

  public Cursor getAlldata() {

   SQLiteDatabase db = this.getWritableDatabase();

   Cursor res = db.rawQuery("select * from " + TABLE_NAME, null);

   return res;

  }

 }

 

 public boolean updateData(String id, String name, String surname, String marks) {

  SQLiteDatabase db = this.getWritableDatabase();

  ContentValues contentValues = new ContentValues();

  contentValues.put(COL1, id);

  contentValues.put(COL2, name);

  contentValues.put(COL3, surname);

  contentValues.put(COL4, marks);

  db.update(TABLE_NAME, contentValues, "ID = ?", new String[] {

   id

  });

  return true;

 }

}

public Integer deleteData(String id) {

 SQLiteDatabase db = this.getWritableDatabase();

 return db.delete(TABLE_NAME, "ID = ? ", new String[] {

  id

 });

}

public class MainActivity extends AppCompatActivity {

 public Button but1;

 

 DatabaseHelper myDb;

 EditText editName, editSurname, editMarks, editTextid;

 Button btnAddData;

 Button btnViewall;

 

 public void init() {

   but1 = (Button) findViewById(R.id.button5);

   but1.setOnClickListener(

    new View.OnClickListener() {

     @Override

     public void onClick(View v) {

      Intent my = new Intent(MainActivity.this, Activity2.class);

      startActivity(my);

     }

    });

   

   @Override

   protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_main);

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);

    setSupportActionBar(toolbar);

    myDb = new DatabaseHelper(this);

    editName = (EditText) findViewById(R.id.editText_name);

    editSurname = (EditText) findViewById((R.id.editText_surname));

    editMarks = (EditText) findViewById((R.id.editText_marks));

    editTextid = (EditText) findViewById(R.id.editText_id);

    btnAddData = (Button) findViewById((R.id.button_add));

    btnViewall = (Button) findViewById(R.id.button_view);

    Adddata();

    viewAll();

    update();

   }

   public void Adddata() {

    btnAddData.setOnClickListener(

     new View.OnClickListener() {

      @Override

      public void onClick(View v) {

       boolean isInserted = myDb.insertData(editName.getText().toString(), editSurname.getText().toString(), editMarks.getText().toString());

       if (isInserted == true)

        Toast.makeText(MainActivity.this, "Data Inserted", Toast.LENGTH_LONG).show();

       else

        Toast.makeText(MainActivity.this, "Data Not Inserted", Toast.LENGTH_LONG).show();

      }

     });

   }

   

   public void update() {

     btnUpdate.setOnClickListener(

       new View.OnClickListener() {

        @Override

        public void onClick(View v) {

         boolean isUpdate = myDb.updateData(editTextid.getText().toString(), editName.getText().toString(), editSurname.getText().toString(), editMarks.getText().toString());

         if (isUpdate == true)

          Toast.makeText(MainActivity.this, "Data Updated", Toast.LENGTH_LONG).show();

         else

          Toast.makeText(MainActivity.this, "Not Updated", Toast.LENGTH_LONG).show();

        }

       }

       

       public void Delete() {

        btnDelete.setOnClickListener(

         new View.OnClickListener() {

          @Override

          public void onClick(View v) {

           Integer deleteRows = myDb.deleteData(editTextid.getText().toString());

           if (deleteRows > 0)

            Toast.makeText(MainActivity.this, "Data Updated", Toast.LENGTH_LONG).show();

          }

         });

       }

       

       

       public void viewAll() {

        btnViewall.setOnClickListener(

          new View.OnClickListener() {

           @Override

           public void onClick(View v) {

             Cursor res = myDb.getAlldata();

             if (res.getCount() == 0) {

              return;

             }

             StringBuffer buffer = new StringBuffer();

             while (res.moveToNext()) {

              buffer.append("id :" + res.getString(0) + "\n");

              buffer.append("name :" + res.getString(1) + "\n");

              buffer.append("surname: " + res.getString(2) + "\n");

              buffer.append("marks: " + res.getString(3) + "\n\n");

Answer 2

公共类 DatabaseHelper 扩展 SQLiteOpenHelper {

public static final String DATABASE_NAME = "student.db";

公共静态最终字符串 TABLE_NAME ="student_table";

public static final String COL1 = "ID";

public static final String COL2 = "NAME";

public static final String COL3 = "SURNAME"

; public static final String COL4 = "MARKS";

公共数据库助手（上下文上下文）{

超级（上下文，DATABASE_NAME，空，1）；

// SQLiteDatabase db = this.getWritableDatabase(); }

公共无效onCreate（SQLiteDatabase db）{

db.execSQL(" 创建表" + TABLE_NAME + "(ID INTEGER PRIMARY KEY AUTOINCREMENT, NAME TEXT, SURNAME TEXT, MARKS INTEGER)" );

}

@覆盖

public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

db.execSQL("DROP TABLE IF EXISTS" + TABLE_NAME);

onCreate(db);

}

公共布尔插入数据（字符串名称，字符串姓氏，字符串标记）{

SQLiteDatabase db = this.getWritableDatabase();

ContentValues contentValues = new ContentValues();

contentValues.put(COL2,name);

contentValues.put(COL3,surname);

contentValues.put(COL4,marks);

长结果= db.insert(TABLE_NAME, null, contentValues);

如果（结果 == -1）

返回假；

别的

返回真；

}

公共游标 getAlldata(){

SQLiteDatabase db = this.getWritableDatabase();

Cursor res = db.rawQuery("select * from " + TABLE_NAME, null );

返回资源；}

}

公共布尔更新数据（字符串 ID，字符串名称，字符串姓氏，字符串标记）{ SQLiteDatabase db = this.getWritableDatabase();

ContentValues contentValues = new ContentValues();

contentValues.put(COL1,id);

contentValues.put(COL2,name);

contentValues.put(COL3,surname);

contentValues.put(COL4,marks);

db.update(TABLE_NAME , contentValues, "ID = ?",new String[]{ id }); 返回真；} }

公共整数删除数据（字符串 ID）{

SQLiteDatabase db = this.getWritableDatabase();

返回 db.delete(TABLE_NAME , "ID = ? ", new String[]{id}); }

公共类 MainActivity 扩展 AppCompatActivity {

公共按钮but1;

数据库助手 myDb；

EditText editName、editSurname、editMarks、editTextid；

按钮 btnAddData;

按钮 btnViewall;

公共无效初始化（）{

but1 = (Button)findViewById(R.id.button5);

but1.setOnClickListener(

新的 View.OnClickListener() {

@覆盖

public void onClick(View v) { Intent my = new Intent(MainActivity.this,Activity2.class); 开始活动（我的）；} });

@覆盖

protected void onCreate(Bundle savedInstanceState) {

super.onCreate (savedInstanceState);

setContentView(R.layout.activity_main);

工具栏工具栏 = (工具栏) findViewById(R.id.toolbar);

setSupportActionBar(工具栏);

myDb = 新的 DatabaseHelper(this);

editName = (EditText)findViewById(R.id.editText_name);

editSurname = (EditText)findViewById((R.id.editText_surname));

editMarks = (EditText)findViewById((R.id.editText_marks));

editTextid = (EditText)findViewById(R.id.editText_id);

btnAddData= (Button)findViewById((R.id.button_add));

btnViewall=(Button)findViewById(R.id.button_view);

添加数据();

查看全部（）;

更新（）;

}

公共无效添加数据（）{

btnAddData.setOnClickListener (

新的 View.OnClickListener() {

@覆盖

public void onClick(View v) {

boolean isInserted = myDb.insertData( editName.getText().toString(), editSurname.getText().toString(), editMarks.getText().toString() );

if(isInserted == true)

Toast.makeText(MainActivity.this ,"数据插入", Toast.LENGTH_LONG).show();

别的

Toast.makeText(MainActivity.this,"未插入数据", Toast.LENGTH_LONG).show(); } }); }

公共无效更新（）{

btnUpdate.setOnClickListener(

新的 View.OnClickListener() {

@覆盖

public void onClick(View v) {

boolean isUpdate = myDb.updateData(editTextid.getText().toString(), editName.getText().toString(), editSurname.getText().toString(), editMarks.getText().toString() );

if(isUpdate == true)

Toast.makeText(MainActivity.this , "数据更新", Toast.LENGTH_LONG).show();

别的

Toast.makeText(MainActivity.this, "Not Updated" , Toast.LENGTH_LONG).show(); } }

公共无效删除（）{

btnDelete.setOnClickListener (

新的 View.OnClickListener() {

@覆盖

public void onClick(View v) {

整数 deleteRows = myDb.deleteData(editTextid.getText().toString());

如果（删除行> 0）

Toast.makeText(MainActivity.this , "数据更新", Toast.LENGTH_LONG).show(); } }); }

公共无效viewAll（）{

btnViewall.setOnClickListener(

新的 View.OnClickListener() {

@覆盖

public void onClick(View v) {

光标 res = myDb.getAlldata();

if(res.getCount() == 0){

返回;

}

StringBuffer 缓冲区 = new StringBuffer();

而（res.moveToNext（））{

buffer.append("id :" + res.getString(0)+ "\n");

buffer.append("name :" + res.getString(1)+ "\n");

buffer.append("姓氏：" + res.getString(2) +"\n");

buffer.append("标记：" + res.getString(3) + "\n\n");

公共最终类 UserProfile {

private UserProfile(){

}

public static UserProfile getProfile(){

    UserProfile userProfile = new UserProfile();

    return userProfile;

}

class Users implements BaseColumn{

    public static final String TABLE_NAME = "UserInfo";

    public static final String COL_ID = "_ID";

    public static final String COL_USERNAME  = "userName ";

    public static final String COL_DOB = "dateOfBirth";

    public static final String COL_GENDER = "Gender";

    public static final String COL_PASSWORD = "Password";

    private int id;

    private String username;

    private String dob;

    private String gender;

    private String password;

    public int getId() {

        return id;

    }

    public void setId(int id) {

        this.id = id;

    }

    public String getUsername() {

        return username;

    }

    public void setUsername(String username) {

        this.username = username;

    }

    public String getDob() {

        return dob;

    }

    public void setDob(String dob) {

        this.dob = dob;

    }

    public String getGender() {

        return gender;

    }

    public void setGender(String gender) {

        this.gender = gender;

    }

    public String getPassword() {

        return password;

    }

    public void setPassword(String password) {

        this.password = password;

    }

}

public Users getUser(){

    Users users = new Users();

    return users;

}

}

Answer 3

似乎此代码行正常工作，并且没有任何问题，请实施并检查它..做得好