如何将SQLite实现到应用程序中？

时间：2017-02-27 03:17:23

标签： android sqlite

我从一个教程中创建了一个简单的SQLite应用程序，现在我正在尝试将它与我制作的游戏拼接在一起。我希望使用SQLite更新和保存高分，但我遇到了一些问题。现在玩游戏但是当我输了并且调用了cancel（）方法时，我得到了一个＆＃34;尝试调用虚拟方法＆＃39; void＆＃39;在null对象引用＆＃34;错误。我不太了解SQL是如何工作的，所以任何反馈都是值得赞赏的。

主要活动

import android.app.Activity;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Button;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;



public class MainActivity extends Activity {

    //sqlite
    //EditText input;
    //first high score
    TextView productText;
    MyDBHandler dbHandler;

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

        //sqlite
        //input = (EditText)findViewById(R.id.editText_ID);
        productText = (TextView)findViewById(R.id.textView1);
        //GameScreen gameScreen = new GameScreen();
        dbHandler = new MyDBHandler(this, null, null, 1);
        updateDatabase();

    }
    public void sendMessage(View view)
    {
        Intent intent = new Intent(MainActivity.this, GameScreen.class);
        startActivity(intent);
    }

    //sqlite
    //add a product to the database
    public void addButtonClicked(){
        GameScreen gameScreen = new GameScreen();
        Products product = new Products(gameScreen.countPassString);
        dbHandler.addProduct(product);
        updateDatabase();
    }

    //sqlite
    public void updateDatabase(){
        String dbString = dbHandler.databaseToString();
        productText.setText(dbString);
    }
}

GameScreen类

import android.app.Activity;
import android.os.CountDownTimer;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.TranslateAnimation;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.TextView;
import android.widget.Toast;



public class GameScreen extends Activity {

    private TextView time;
    private ImageButton start;
    private ImageButton gameButton;
    private ImageButton button2;
    private CountDownTimer countDownTimer;
    public static int count = 0;
    public static int countPass = 0;
    public String countPassString = "";

    final Handler handler = new Handler();
    final Runnable r = new Runnable() {
        public void run() {
            cancel();
        }
    };




    private View.OnClickListener btnClickListener = new  View.OnClickListener(){

        @Override
        public void onClick(View v) {

            switch(v.getId()){
                case R.id.start_ID :
                    start();
                    break;
                case R.id.gameButton_ID :
                    gameButton();
                    break;
                case R.id.button2_ID :
                    button2();
                    break;
            }

        }


    };


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


        start = (ImageButton) findViewById(R.id.start_ID);
        start.setOnClickListener(btnClickListener);
        time = (TextView) findViewById(R.id.time);
        gameButton = (ImageButton) findViewById(R.id.gameButton_ID);
        gameButton.setOnClickListener(btnClickListener);
        button2 = (ImageButton) findViewById(R.id.button2_ID);
        button2.setOnClickListener(btnClickListener);

        button2.setVisibility(View.GONE);

    }

    public void start(){

        count = 0;
        start.setVisibility(View.GONE);

        time.setText("100");
        //this doesnt work and makes app crash when you hit start button

        countDownTimer = new CountDownTimer(100 * 1000, 1000) {
            @Override
            public void onTick(long millsUntilFinished){
                time.setText("" + millsUntilFinished / 1000);

                //turns textview string to int
                int foo = Integer.parseInt(time.getText().toString());

                if(foo == 93) {
                    time.setVisibility(View.GONE);
                    button2.setVisibility(View.VISIBLE);
                }
                else if(foo == 97) {


gameButton.animate().translationX(200).setDuration(5000).start(); // move away
                }
                else if(foo == 90){
                    gameButton.animate().translationY(200).setDuration(5000).start(); // move away
                }

                if(foo  % 2 == 0){

                    handler.postDelayed(r, 1000);

                }
            }

            public void onFinish() {
                start.setVisibility(View.VISIBLE);
                time.setVisibility(View.VISIBLE);
                time.setText("Done !");

                //need to check if score will reset if you win the game

                Toast.makeText(getApplicationContext(), "You scored " + count, Toast.LENGTH_LONG).show();
                gameButton.clearAnimation();
                gameButton.animate().translationX(0).setDuration(500).start(); //move back
                gameButton.animate().translationY(0).setDuration(500).start(); //move back
                button2.setVisibility(View.GONE);
            }
        };
        countDownTimer.start();
    }

    private void cancel(){
        if(countDownTimer != null){
            countDownTimer.cancel();
            countDownTimer = null;
            start.setVisibility(View.VISIBLE);
            time.setVisibility(View.VISIBLE);
            gameButton.clearAnimation();
            gameButton.animate().translationX(0).setDuration(500).start(); //move back
            gameButton.animate().translationY(0).setDuration(500).start(); //move back
            button2.setVisibility(View.GONE);

            //holds score at end of game
            countPass = count;
            //reset score for new game
            count = 0;
            Toast.makeText(getApplicationContext(), "You scored " + countPass, Toast.LENGTH_LONG).show();
            countPassString = Integer.toString(countPass);
            MainActivity mainActivity = new MainActivity();
            mainActivity.addButtonClicked();
        }
    }

    private void gameButton(){


        int foo = Integer.parseInt(time.getText().toString());

        if(foo  % 2 == 0 ) {
            final Toast toast = Toast.makeText(getApplicationContext(), "+1", Toast.LENGTH_SHORT);
            toast.show();

            // makes +1 toast half a second
            Handler gameButtonToastHandler = new Handler();
            gameButtonToastHandler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    toast.cancel();
                }
            }, 500);

            handler.removeCallbacks(r);
            ++count;
        }
        else{
            cancel();
        }
    }

    private void button2(){
        cancel();
    }

}

MyDBHandler类

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 = "products.db";
public static final String TABLE_PRODUCTS = "products";
public static final String COLUMN_ID = "_id";
public 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);
}

//add a new row to the database
public void addProduct(Products product){
    ContentValues values = new ContentValues();
    values.put(COLUMN_PRODUCTNAME, product.get_productname());
    SQLiteDatabase db = getWritableDatabase();
    db.insert(TABLE_PRODUCTS, null, values);
    db.close();
}

/*//delete a product from the database
public void deleteProduct(String productName){
    SQLiteDatabase db = getWritableDatabase();
    db.execSQL("DELETE FROM " + TABLE_PRODUCTS + " WHERE " + COLUMN_PRODUCTNAME + "=\"" + productName + "\";" );
}
*/

//print out the database as a string
public String databaseToString(){
    String dbString = "";
    SQLiteDatabase db = getWritableDatabase();
    String query = "SELECT * FROM " + TABLE_PRODUCTS + " WHERE 1";


    //Cursor point to location in your results
    /*
    Cursor c = db.rawQuery(query, null);
    //Move to the first row in your results
    c.moveToFirst();

    while(!c.isAfterLast()){
        if(c.getString(c.getColumnIndex("productname")) != null){
            dbString += c.getString(c.getColumnIndex("productname"));
            dbString += "\n";
        }
        c.moveToNext();
    }
    */

    db.close();
    return dbString;

}

}

产品类

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

public Products(){

}

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

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;
}
}

MainActivity的XML也是我试图让SQL更改textViews的地方。

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:background="@drawable/clock"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.emilythacker.myapplication.MainActivity">

<TextView
    android:text="HIGH SCORES"
    android:textSize="35dp"
    android:textColor="#4cfd00"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="45dp"
    android:id="@+id/textView" />

<TextView
    android:text="1:"
    android:textSize="35dp"
    android:textColor="#4cfd00"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="17dp"
    android:id="@+id/textView1"
    android:layout_below="@+id/textView"
    android:layout_alignStart="@+id/textView" />

<TextView
    android:text="2:"
    android:textSize="35dp"
    android:textColor="#4cfd00"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignStart="@+id/textView1"
    android:id="@+id/textView2"
    android:layout_below="@+id/textView1" />

<TextView
    android:text="3:"
    android:textSize="35dp"
    android:textColor="#4cfd00"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/textView3"
    android:layout_below="@+id/textView2"
    android:layout_alignStart="@+id/textView2" />

<TextView
    android:text="4:"
    android:textSize="35dp"
    android:textColor="#4cfd00"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/textView4"
    android:layout_below="@+id/textView3"
    android:layout_alignStart="@+id/textView3" />

<TextView
    android:text="5:"
    android:textSize="35dp"
    android:textColor="#4cfd00"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/textView5"
    android:layout_below="@+id/textView4"
    android:layout_alignStart="@+id/textView4" />

<Button
    android:text="PLAY"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/textView5"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="53dp"
    android:id="@+id/playbutton_ID"
    android:onClick="sendMessage"/>

</RelativeLayout>

这是控制台消息

    D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.emilythacker.myapplication, PID: 31291
                  java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.emilythacker.myapplication.MyDBHandler.addProduct(com.example.emilythacker.myapplication.Products)' on a null object reference
                      at com.example.emilythacker.myapplication.MainActivity.addButtonClicked(MainActivity.java:46)
                      at com.example.emilythacker.myapplication.GameScreen.cancel(GameScreen.java:150)
                      at com.example.emilythacker.myapplication.GameScreen.access$000(GameScreen.java:19)
                      at com.example.emilythacker.myapplication.GameScreen$1.run(GameScreen.java:33)
                      at android.os.Handler.handleCallback(Handler.java:751)
                      at android.os.Handler.dispatchMessage(Handler.java:95)
                      at android.os.Looper.loop(Looper.java:154)
                      at android.app.ActivityThread.main(ActivityThread.java:6688)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358)
Disconnected from the target VM, address: 'localhost:8603', transport: 'socket'

1 个答案:

答案 0 :(得分：0)

你应该添加

  

SQLiteDatabase db = this.getWritableDatabase（）;

在Contentvalues之前

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