Question

我想获取一个输入字符串，然后单击Add it it it how under show，依此类推但是当我点击＆＃34;添加＆＃34;按钮它得到了坚持。而不是在那里展示。

我的MainActivity布局：

MainActivity.java

package com.theaditya.sqlitewala;
   import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.EditText;
    import android.widget.TextView;

    public class MainActivity extends AppCompatActivity {

        EditText adiInput;
        TextView adiText;
        MyDbHandler dbHandler;

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

            adiInput =(EditText) findViewById(R.id.adiInput);
            adiText =(TextView)findViewById(R.id.adiText);

            dbHandler=new MyDbHandler(this,null,null,1);
            printDatabase();
        }
        public void printDatabase(){
            String dbString= dbHandler.databaseToString();
            adiText.setText(dbString);
            adiInput.setText("");
        }
        public void addButtonClicked(View view){
            Products products= new Products(adiInput.getText().toString());
            dbHandler.addProduct(products);
            printDatabase();
        }
        public void deleteButtonClicked(View view){
            String inputText =adiInput.getText().toString();
            dbHandler.deleteProduct(inputText);
            printDatabase();
        }
    }

MyDbHandler.java

package com.theaditya.sqlitewala;

    import android.content.ContentValues;
    import android.content.Context;
    import android.database.Cursor;
    import android.database.sqlite.SQLiteDatabase;
    import android.database.sqlite.SQLiteOpenHelper;

    public class MyDbHandler extends SQLiteOpenHelper {
        private static final int DATABASE_VERSION=1;
        private static final String DATABASE_NAME="product.db";
        private static final String TABLE_PRODUCTS="products";      //its the TABLE NAME
        private static final String COLUMN_ID="id";
        private static final String COLUMN_PRODUCTNAME="productname";

        public MyDbHandler(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
            super(context, DATABASE_NAME, factory, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            String query="CREATE TABLE "+ TABLE_PRODUCTS +" ("+
                    COLUMN_ID +" INTEGER PRIMARY KEY AUTOINCREMENT, "+
                    COLUMN_PRODUCTNAME +" TEXT"+
                    ");" ;
            db.execSQL(query);
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            db.execSQL("DROP TABLE IF EXISTS "+ TABLE_PRODUCTS);
            onCreate(db);
        }
        //for adding new Row to DataBase
        public void addProduct(Products products){
            ContentValues values=new ContentValues();
            values.put(COLUMN_PRODUCTNAME,products.get_productname());
            SQLiteDatabase db=getWritableDatabase();
            db.insert(TABLE_PRODUCTS,null,values);
            db.close();
        }

        //for deleting Row to DataBase
        public void deleteProduct(String productName){
            SQLiteDatabase db=getWritableDatabase();
            db.execSQL("DELETE FROM "+TABLE_PRODUCTS+" WHERE "+COLUMN_PRODUCTNAME+"=\""+productName+"\";" );
        }

        public String databaseToString(){
            String dbString="";
            SQLiteDatabase db=getWritableDatabase();
            String query="SELECT * FROM "+TABLE_PRODUCTS+" WHERE 1";

            //cursor points to the location of ur result
            Cursor c=db.rawQuery(query,null);
            //move to the first row in result
            c.moveToFirst();
            while (!c.isAfterLast()) {
                if (c.getString(c.getColumnIndex("productname")) != null) {
                    dbString += c.getString(c.getColumnIndex("productname"));
                    dbString += "\n";
                }
            }
            db.close();
            return dbString;
        }
    }

Product.java

package com.theaditya.sqlitewala;

public class Products {
    private int _id;
    private String _productname;

    public Products(String _productname) {
        this._productname = _productname;
    }
    public Products() {
    }


    public void set_id(int _id) {
        this._id = _id;
    }

    public void set_productname(String _productname) {
        this._productname = _productname;
    }

    public int get_id() {
        return _id;
    }

    public String get_productname() {
        return _productname;
    }
}

Answer 1

你的databaseToString（）方法查询错误：

如果你想得到以下数据库的第一行将起作用：

public String databaseToString() {

    // String query = "SELECT * FROM " + TABLE_PRODUCTS + " WHERE 1";
    String query = "SELECT * FROM " + TABLE_PRODUCTS + " ORDER BY "
            + COLUMN_ID + " DESC LIMIT 1";

    SQLiteDatabase db = this.getWritableDatabase();
    Cursor cursor = db.rawQuery(query, null);
    String str = "";
    if (cursor.moveToFirst())
        str = cursor.getString(cursor.getColumnIndex(COLUMN_PRODUCTNAME));
    cursor.close();

    return str;
}

从代码中获取db的所有记录将起作用：

 public String databaseToString() {

        String query = "SELECT * FROM " + TABLE_PRODUCTS ;

        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(query, null);
        String str = "";
            if (cursor.moveToFirst()) {
                do {
                            str = cursor.getString(cursor.getColumnIndex(COLUMN_PRODUCTNAME)) +"\n";

                } while (cursor.moveToNext());
            }

        cursor.close();

        return str;
    }

Android sqlite应用程序在向数据库添加产品时遇到困难

1 个答案: