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我想将我的数据从 db 显示到条形图（Achartengine），我有两个字段日期和 bmi 结果。日期为字符串格式，bmi 为 double/int。

这是我迄今为止尝试过的：

public class BMICalculatorDB {
public static final String KEY_BMIID = "bmi_id";
public static final String KEY_BMIDATA = "bmi_data";
public static final String KEY_BMIDATE = "bmi_date";

private static final String DATABASE_NAME = "DB_bmi";
private static final String DATABASE_TABLE = "tbl_bmi";
private static final int DATABASE_VERSION = 1;

private DBHelper ourHelper;
private final Context ourContext;
private SQLiteDatabase ourDatabase;

private static class DBHelper extends SQLiteOpenHelper{

    public DBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        // TODO Auto-generated constructor stub
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // TODO Auto-generated method stub
        db.execSQL( "CREATE TABLE " + DATABASE_TABLE + " (" +
        KEY_BMIID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                KEY_BMIDATA + " TEXT NOT NULL, " +
                KEY_BMIDATE + " TEXT NOT NULL );"
                );
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub
        db.execSQL( "DROP TABLE IF EXISTS " + DATABASE_TABLE );
        onCreate(db);
    }

}

public BMICalculatorDB(Context c){
    ourContext = c;
}

public BMICalculatorDB open(){
    ourHelper = new DBHelper(ourContext);
    ourDatabase = ourHelper.getWritableDatabase();
    return this;
}

public void close(){
    ourHelper.close();
}

public long createEntry( String data, String date ) {
    //, String date 
    // TODO Auto-generated method stub
    ContentValues cv = new ContentValues();
    cv.put(KEY_BMIDATA, data);
    cv.put(KEY_BMIDATE, date);
    return ourDatabase.insert(DATABASE_TABLE, null, cv);
}

public String getBMIID() {
    // TODO Auto-generated method stub
    String[] column =
            new String[]{ KEY_BMIID };
    Cursor c = 
            ourDatabase.query(DATABASE_TABLE, column, null, null, null, null, null);

    String result = "";
    int iID = c.getColumnIndex(KEY_BMIID);

    for ( c.moveToFirst(); ! c.isAfterLast(); c.moveToNext() ){
        result = result + c.getString(iID);
    }

    return result;
}

public String getBMIDataData(){

    String[] column =
                new String[]{ KEY_BMIDATA };
        Cursor c = 
                ourDatabase.query( DATABASE_TABLE, column, null, null, null, null, null );

        String result = "";
        int iData = c.getColumnIndex( KEY_BMIDATA );

        for ( c.moveToFirst(); ! c.isAfterLast(); c.moveToNext() ){
            result = result + c.getString( iData );
        }


    return result;
}

public String getBMIDateData(){
    String[] column =
            new String[]{ KEY_BMIDATE };
    Cursor c = 
            ourDatabase.query( DATABASE_TABLE, column, null, null, null, null, null );

    String result = "";
    int iDate = c.getColumnIndex( KEY_BMIDATE);

    for ( c.moveToFirst(); ! c.isAfterLast(); c.moveToNext() ){
        result = result + c.getString( iDate );
    }


return result;
}

public void updateEntry( long lId, String mData, String mDate ) {
    // TODO Auto-generated method stub
    ContentValues cvUpdate = new ContentValues();

    cvUpdate.put( KEY_BMIDATA, mData );
    cvUpdate.put( KEY_BMIDATE, mDate );
    ourDatabase.update( DATABASE_TABLE, cvUpdate, KEY_BMIID + " = lId", null );
}

public String getData(long l) {
    // TODO Auto-generated method stub
    return null;
}

public String getDate(long l) {
    // TODO Auto-generated method stub
    return null;
}

public XYMultipleSeriesDataset getDemoDataset(String title) {

    String[] column =
            new String[]{ KEY_BMIDATA };
    Cursor c = ourDatabase.query( DATABASE_TABLE, column, null, null, null, null, null );

    XYMultipleSeriesDataset dataset = new XYMultipleSeriesDataset();

    TimeSeries series = new TimeSeries("Line1");
    TimeSeries series2 = new TimeSeries(title);

    getBMIDataData();

    while (!c.isAfterLast()) {
        int date = c.getInt((Integer) c.getColumnIndexOrThrow("bmi_date"));
        int weight = c.getInt((Integer) c.getColumnIndexOrThrow("bmi_data"));
        series2.add(weight, date);
        c.moveToNext();
    }

    c.close();

    dataset.addSeries(series);
    dataset.addSeries(series2);

    return dataset;
}


public Intent getIntent(Context context) {

    //Lager TimeSeries for den første linja
    XYMultipleSeriesDataset dataset = getDemoDataset("Line1");

    //Kode for render
    XYMultipleSeriesRenderer mRenderer = new XYMultipleSeriesRenderer();

    //Optimalisering linje1
    XYSeriesRenderer renderer = new XYSeriesRenderer();
    renderer.setColor(Color.YELLOW);
    renderer.setPointStyle(PointStyle.CIRCLE);
    renderer.setFillPoints(true);

    // Optimalisering linje2 husk rekke følgen
    XYSeriesRenderer renderer2 = new XYSeriesRenderer();
    renderer2.setColor(Color.BLUE);
    renderer2.setPointStyle(PointStyle.SQUARE);
    renderer2.setFillPoints(true);

    //Legger til render seriene
    mRenderer.addSeriesRenderer(renderer);

    //Optimalisering grafen
    mRenderer.setChartTitle("Test");
    mRenderer.setZoomEnabled(true);
    mRenderer.setZoomButtonsVisible(true);
    mRenderer.setBackgroundColor(Color.BLACK);
    mRenderer.setApplyBackgroundColor(true);
    mRenderer.setXTitle("Dager");
    mRenderer.setShowGrid(true);

    mRenderer.addSeriesRenderer(renderer2);


    Intent intent = ChartFactory.getLineChartIntent(context, dataset, 
            mRenderer, "Line Graph Title");

    return intent;

}

}

但我在第 28 行遇到错误： 

Cursor c = dbSqlite.query( DATABASE_TABLE, column, null, null, null, null, null );

和 

XYMultipleSeriesDataset dataset = getDemoDataset("Line1");

我真的坚持这一点。任何帮助都非常感谢。

错误：

11-11 02:33:06.542: E/AndroidRuntime(344): FATAL EXCEPTION: main
11-11 02:33:06.542: E/AndroidRuntime(344): java.lang.NullPointerException
11-11 02:33:06.542: E/AndroidRuntime(344):  at   android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:118)
11-11 02:33:06.542: E/AndroidRuntime(344):  at com.fps.iHealthFirst.calculators.LineGraph.getDemoDataset(LineGraph.java:53)
11-11 02:33:06.542: E/AndroidRuntime(344):  at com.fps.iHealthFirst.calculators.LineGraph.getIntent(LineGraph.java:87)
11-11 02:33:06.542: E/AndroidRuntime(344):  at com.fps.iHealthFirst.calculators.BMICalculator.onClick(BMICalculator.java:181)
11-11 02:33:06.542: E/AndroidRuntime(344):  at android.view.View.performClick(View.java:2485)
11-11 02:33:06.542: E/AndroidRuntime(344):  at android.view.View$PerformClick.run(View.java:9080)
11-11 02:33:06.542: E/AndroidRuntime(344):  at android.os.Handler.handleCallback(Handler.java:587)
11-11 02:33:06.542: E/AndroidRuntime(344):  at android.os.Handler.dispatchMessage(Handler.java:92)
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