Question

每当我运行应用程序时，我都会面临这个问题第一次数据库中的数据保持单次，但是当我关闭应用程序并再次重新启动时数据会变为两次（表示表中的两行相同）。类似于第3次，第4次等等上。我该如何摆脱这个问题？我甚至在DataList.java中放了datas.clear但是不管我是否在正确的位置添加了datas.clear（）行。如果我的代码中有任何其他问题，请帮助PLZ。

MainActivity.java代码

public class MainActivity extends AppCompatActivity {

Button listButton, addButton;
DatabaseHelper df;
private final static String TAG = "TestActivity";

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

    df = new DatabaseHelper(this);

     addButton = (Button) findViewById(R.id.addbutton);
    uploadList();
}

public void uploadList(){
      DatabaseHelper df=new DatabaseHelper(this);
            df.open();
            try{
                InputStream im=getResources().getAssets().open("testdata.csv");
                BufferedReader br=new BufferedReader(new InputStreamReader(im));
                String data=br.readLine();
                while(data != null){
                    String t[]=data.split(",");
                    Product p=new Product();
                    p.setFirst(t[0]);
                    p.setSec(t[1]);
                    p.setThird(t[2]);
                    df.insert(p);
                    data=br.readLine();
                }
            }catch(Exception e){

            }

}
}

DatabaseHelper.java代码

public class DatabaseHelper extends SQLiteOpenHelper{

private static final String FIRST="Name";
private static final String SECOND="Issn";
private static final String THIRD="ImpactFactor";

private static final String DATABASE="journal2016";
private static final String TABLENAME="journal";

private static final int VERSION=1;

SQLiteDatabase sd;

public void open(){
    sd=getWritableDatabase();
}
public void close(){
    sd.close();
}

public DatabaseHelper(Context context) {
    super(context, DATABASE, null, VERSION);
}

@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
    sqLiteDatabase.execSQL("DROP TABLE IF EXISTS " + TABLENAME );
    sqLiteDatabase.execSQL("CREATE TABLE " + TABLENAME + " ( NAME  TEXT, ISSN  TEXT, IMPACTFACTOR  REAL)");
}

@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
    sqLiteDatabase.execSQL("DROP TABLE IF EXISTS " + TABLENAME );
}



public long insert(Product p){
    ContentValues cv=new ContentValues();
    cv.put(FIRST, p.getFirst());
    cv.put(SECOND, p.getSec());
    cv.put(THIRD, p.getThird());
    return sd.insertWithOnConflict(TABLENAME, null, cv,SQLiteDatabase.CONFLICT_REPLACE);

}

public List<Product> getAllProduct(){
    ArrayList<Product> list=new ArrayList<Product>();
    SQLiteDatabase db = this.getWritableDatabase();
    Cursor c=db.rawQuery("SELECT * FROM " + TABLENAME, null);
    while(c.moveToNext()){
        Product p=new Product();
        p.setFirst(c.getString(0));
        p.setSec(c.getString(1));
        p.setThird(c.getString(2));
        list.add(p);
    }
    db.close();
    return list;
}
}

DataList.java代码

public class DataList extends Activity{

List<Product> datas = new ArrayList<Product>();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.list);
    datas.clear();
    DatabaseHelper d=new DatabaseHelper(this);
    d.open();
    datas  = d.getAllProduct();
    ListView lv=(ListView)findViewById(R.id.listView1);
    lv.setAdapter(new ArrayAdapter(this, android.R.layout.simple_list_item_1, datas));
}

}

Product.java

public class Product {
private String first;
private String second;
private String third;
public String getFirst() {
    return first;
}
public void setFirst(String first) {
    this.first = first;
}
public String getSec() {
    return second;
}
public void setSec(String sec) {
    this.second = sec;
}
public String getThird() {
    return third;
}
public void setThird(String third) {
    this.third = third;
}

@Override
public String toString() {

    return first + second + third;
}

}

Answer 1

从onCreate()方法中删除此行：

df = new DatabaseHelper(this);

因为您在DatabaseHelper方法中创建了uploadList()类的对象，所以不需要它。此外，您在uploadList()内调用了onCreate()方法，这就是为什么每次启动应用时，onCreate()方法都会执行，而您uploadList()也会执行。尝试将其调用语句放在onClickListener中，以便在单击按钮或选择的内容时发生。

重启Android数据库中的应用程序时重复的数据

1 个答案: