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我正在做Android開發的第一次。我需要將我的數據庫分解成碎片，我得到這個異常 - 任何人都可以幫助我並找到我的錯誤嗎？碎片中的SQLite數據庫 - Android Studio
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
DatabaseHelper：
public class DatabaseHelper extends SQLiteOpenHelper {
public static final String DATABASE_NAME = "hunderassen.db";
public static final String TABLE_NAME = "hunderassen_table";
public static final String COLUMN1 = "ID";
public static final String COLUMN2 = "name_Hunderasse";
public static final String COLUMN3 = "durchschnittlicheDauer";
public static final String COLUMN4 = "groesseHund";
public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, 1); //creating db and table
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("create table " + TABLE_NAME + " (ID INTEGER PRIMARY KEY AUTOINCREMENT, name_Hunderasse TEXT, durchschnittlicheDauer TEXT, groesseHund TEXT) ");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("drop table if exists " + TABLE_NAME);
this.onCreate(db);
}
public boolean insertData(String name_hr, String durchschnitt, String groesse) {
SQLiteDatabase database = this.getWritableDatabase();
ContentValues contentValues = new ContentValues();
contentValues.put(COLUMN2, name_hr);
contentValues.put(COLUMN3, durchschnitt);
contentValues.put(COLUMN4, groesse);
long result = database.insert(TABLE_NAME, null, contentValues);
//check if value is -1
if (result == -1) {
return false;
} else {
return true;
}
}
和碎片：
public class Fragment3 extends Fragment {
DatabaseHelper myDB;
EditText editHunderasse, editDurchschnitt, editGroesse, editID;
Button btnADD;
Button btnView;
Button btnUpdate;
Button btnDelete;
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstance) {
View rootView = inflater.inflate(R.layout.fragment3_layout, container, false);
return rootView;
}
/**
* if (container == null) {
* return null;
* }
* return inflater.inflate(R.layout.fragment3_layout, container, false);
* }
**/
@Override
public void onCreate(Bundle saveInstanceState) {
super.onCreate(saveInstanceState);
myDB = new DatabaseHelper(getActivity());
editHunderasse = (EditText) getView().findViewById(R.id.editText_Hunderasse);
editDurchschnitt = (EditText) getView().findViewById(R.id.editText_Dauer);
editGroesse = (EditText) getView().findViewById(R.id.editText_Groesse);
btnADD = (Button) getView().findViewById(R.id.button_add);
btnView = (Button) getView().findViewById(R.id.button_view);
btnUpdate = (Button) getView().findViewById(R.id.button_update);
editID = (EditText) getView().findViewById(R.id.editText_id);
btnDelete = (Button) getView().findViewById(R.id.button_delete);
addData(); //aufrufen der Methode addData
}
public void addData() {
btnADD.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
myDB.insertData(
editHunderasse.getText().toString(),
editDurchschnitt.getText().toString(),
editGroesse.getText().toString()
);
}
});
}
XML - 文件：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hunderasse"
android:id="@+id/textView3" />
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/editText_Hunderasse" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Dauer"
android:id="@+id/textView4" />
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/editText_Dauer"
android:layout_gravity="center_horizontal" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Größe"
android:id="@+id/textView17" />
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/editText_Groesse" />
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/editText_id" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="ADD"
android:id="@+id/button_add"
android:clickable="false"
android:enabled="true"
android:focusable="false" />
也許任何人都可以幫忙嗎？非常感謝！
發生異常的線是什麼？ –
btnADD.setOnClickListener（new View.OnClickListener（）它說有一個空引用，但我不知道爲什麼 – christina