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.java

package 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