java - 我是 android 领域的新手，并且遇到插入 android 应用程序的问题？

Question

我做了一个简单的插入形式，它将三个数字作为输入存储在数据库中（请注意我正在使用 sqlite 数据库）。所以主要的是当我点击提交时，它会出现一个错误，上面写着没有这样的表：-messgae_table。我试图找出我的代码有什么问题，但对我来说什么都没有解决！！！！请帮帮我......

Activity.java 主页面：-

button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                try{
                    DatabaseQueries db=new DatabaseQueries(Main2Activity.this);
                    Log.e("data",editText1.getText().toString());
                    long result=db.addMessageNumber(editText1.getText().toString(),editText2.getText().toString(),editText3.getText().toString());
                    if (result>0){
                        Toast.makeText(Main2Activity.this, "Inserted", Toast.LENGTH_SHORT).show();
                    }
                    else {
                        Toast.makeText(Main2Activity.this, "Not Inserted", Toast.LENGTH_SHORT).show();
                    }
                }
                catch (Exception e){
                    e.getMessage();
                    e.printStackTrace();

                }

DatabaseColumn.java:-

public static final String MESSAGE_TABLE = "message_table";
    public static final String MESSAGE_NUMBERONE = "message_numberone";
    public static final String MESSAGE_NUMBERTWO = "messgae_numbertwo";
    public static final String MESSAGE_NUMBERTHREE = "message_numberthree";

数据库创建：-

public class DatabaseCreation extends SQLiteOpenHelper {
    private static String DB_NAME = "secure.db";
    private static int DB_VERSION = 1;


    private String message_table = "CREATE TABLE " + DatabaseColumn.MESSAGE_TABLE + " ( " + DatabaseColumn.MESSAGE_NUMBERONE + " TEXT, " + DatabaseColumn.MESSAGE_NUMBERTWO + " TEXT, " + DatabaseColumn.MESSAGE_NUMBERTHREE + " TEXT )";

    public DatabaseCreation(Context context){

        super(context, DB_NAME,null,DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        sqLiteDatabase.execSQL(contact_table);
        sqLiteDatabase.execSQL(message_table);

    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

    }
}

数据库查询：-

public long addMessageNumber(String numberone, String numbertwo, String numberthree){
        SQLiteDatabase sqLiteDatabase2=db.getWritableDatabase();
        ContentValues cv=new ContentValues();
        cv.put(DatabaseColumn.MESSAGE_NUMBERONE,numberone);
        cv.put(DatabaseColumn.MESSAGE_NUMBERTWO,numbertwo);
        cv.put(DatabaseColumn.MESSAGE_NUMBERTHREE,numberthree);
        long result=sqLiteDatabase2.insert(DatabaseColumn.MESSAGE_TABLE,null,cv);
        sqLiteDatabase2.close();
        return result;
    }

标签： javaandroidsqlite

Answer 1

您的代码，除了那一行之外，sqLiteDatabase.execSQL(contact_table);在拼凑在一起时似乎可以工作。

• 上面的行被注释掉了。

因此，您的问题可能是您习惯于onCreate每次运行应用程序时都运行。即当一个活动开始时。但是，SQLiteOpenHelper'sonCreate方法仅在创建数据库时运行一次。任何其他时间（即数据库存在时）它都不会运行。

因此，您的问题可能是找不到该表，因为它尚未创建，因为您已将代码添加到onCreate（以创建表）而不删除数据库。

使固定 ：-

FIX是执行以下操作之一：-

• 通过设置删除应用程序的数据，或
• 卸载应用程序（删除应用程序的数据）

完成上述其中一项操作后，重新运行应用程序，这可能会让您通过 Table not found 错误。

用于测试的代码：-

数据库列.java

public class DatabaseColumn {
    public static final String MESSAGE_TABLE = "message_table";
    public static final String MESSAGE_NUMBERONE = "message_numberone";
    public static final String MESSAGE_NUMBERTWO = "messgae_numbertwo";
    public static final String MESSAGE_NUMBERTHREE = "message_numberthree";
}

数据库创建.java

public class DatabaseCreation extends SQLiteOpenHelper {
    private static String DB_NAME = "secure.db";
    private static int DB_VERSION = 1;

    private String message_table =
            "CREATE TABLE " + DatabaseColumn.MESSAGE_TABLE + " ( " +
                    DatabaseColumn.MESSAGE_NUMBERONE + " TEXT, " +
                    DatabaseColumn.MESSAGE_NUMBERTWO + " TEXT, " +
                    DatabaseColumn.MESSAGE_NUMBERTHREE + " TEXT )";

    public DatabaseCreation(Context context){
        super(context, DB_NAME,null,DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        //sqLiteDatabase.execSQL(contact_table); //<<<<<<<< ?????????
        sqLiteDatabase.execSQL(message_table);
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
    }
}

-注意注释掉的行（您可能不必将其注释掉）

数据库查询.java

public class DatabaseQueries {
    DatabaseCreation db;

    public DatabaseQueries(Context context) {
        db =  new DatabaseCreation(context);
    }

    //!!!!!!!!!! Code other than this block has been assumed
    public long addMessageNumber(String numberone, String numbertwo, String numberthree){
        SQLiteDatabase sqLiteDatabase2=db.getWritableDatabase();
        ContentValues cv=new ContentValues();
        cv.put(DatabaseColumn.MESSAGE_NUMBERONE,numberone);
        cv.put(DatabaseColumn.MESSAGE_NUMBERTWO,numbertwo);
        cv.put(DatabaseColumn.MESSAGE_NUMBERTHREE,numberthree);
        long result=sqLiteDatabase2.insert(DatabaseColumn.MESSAGE_TABLE,null,cv);
        sqLiteDatabase2.close();
        return result;
    }
}

• 注意见评论

MainActivity.java

public class MainActivity extends AppCompatActivity {

    Button button;
    EditText editText1,editText2,editText3;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button = this.findViewById(R.id.button);
        editText1 = this.findViewById(R.id.edittext1);
        editText2 = this.findViewById(R.id.edittext2);
        editText3 = this.findViewById(R.id.edittext3);

        //!!!!!!!!!! Code other than this block has been assumed
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                try {
                    //!!!!!!!!!! view.getContext() used instead of Main2Activity.this (code is easier to copy elsewhere)
                    DatabaseQueries db = new DatabaseQueries(view.getContext());
                    Log.e("data", editText1.getText().toString());
                    long result = db.addMessageNumber(
                            editText1.getText().toString(),
                            editText2.getText().toString(),
                            editText3.getText().toString()
                    );
                    if (result > 0) {
                        Toast.makeText(view.getContext(), "Inserted", Toast.LENGTH_SHORT).show();
                        Log.e("INSERTINFO","Row inserted."); //<<<<<<<<< ADDED FOR TESTING
                    } else {
                        Toast.makeText(view.getContext(), "Not Inserted", Toast.LENGTH_SHORT).show();
                        Log.e("INSERTINFO","Row NOT inserted."); //<<<<<<<<< ADDED FOR TESTING
                    }
                } catch (Exception e) {
                    e.getMessage();
                    e.printStackTrace();
                }
            }
        });
    }
}

• 注意MainActivity 用于测试而不是 Main2Activity
• 见评论。
• 吐司的补充是伐木。

测试结果

启动时首次运行：-

插入

在三个 EditTexts 中输入 T1、T2 和 T3 并单击 CLICKME 按钮后，日志包含：-

2019-11-29 07:13:49.056 E/data: T1
2019-11-29 07:13:49.093 E/INSERTINFO: Row inserted.