我一天中的大部分时间都在使用此应用程序，并创建了一个存储客户信息的SQLite数据库。我有选择从SQLite数据库中更新和删除项目的选项，但无法弄清为什么它不起作用（或应该如何起作用）。我可以添加到数据库，但是不能编辑或删除信息。当我单击列表视图项时显示特定信息时，我也会遇到问题。当我尝试删除时，应用程序崩溃：
Button addBtn1 = (Button)findViewById(R.id.deleteCust);
addBtn1.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v){
Cursor cursor = datasource.displayCurrentCustomer();
if( cursor != null) {
String where = CustDBOpenHelper.CustID + "=" + dbOpenHelper.CustID;
database.delete(CustDBOpenHelper.TABLE_NAME, where, null);
startActivity(new Intent(EditCustomers.this, CustomerView.class));
}
}
});
这是帮手：
public class CustDBOpenHelper extends SQLiteOpenHelper {
private static final String LOGTAG = "test";
private static final String DATABASE_NAME = "CARDEALER.db";
private static final int DATABASE_VERSION = 1;
public static final String TABLE_NAME = "CUSTOMER_TABLE";
public static final String CustID = "cust_id";
public static final String FirstName = "first_name";
public static final String LastName = "last_name";
public static final String CarMake = "car_make";
public static final String CarModel = "car_model";
public static final String CarCost = "car_cost";
private static final String TABLE_CREATE =
" CREATE TABLE " + TABLE_NAME + " (" +
CustID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
FirstName + " TEXT, "+
LastName + " TEXT, " +
CarMake + " TEXT, " +
CarModel + " TEXT, " +
CarCost + " NUMERIC " + ")";
public CustDBOpenHelper(Context context ) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db){
db.execSQL(TABLE_CREATE);
Log.i(LOGTAG, "Table created");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int NewVersion){
db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
onCreate(db);
}
}
我已经在这里待了太久了，可能很容易忽略某些东西，但是我目前正处于一个断点。.我假设一旦我弄清楚了如何删除或更新当前的SQLite数据库，事情就会变得容易些，但是我有尝试了一切，至少似乎是我有。我猜问题的一部分就是单击列表视图项时显示的内容，因为它始终显示SQLite数据库的第一项。这段代码是：
List<Custs> custs = datasource.findAll();
if (custs.size() == 0) {
Toast.makeText(this,"No customer information to show", Toast.LENGTH_SHORT).show();
}
ArrayAdapter<Custs> adapter = new ArrayAdapter<Custs>(this, android.R.layout.simple_list_item_1 , custs);
ListView lv = (ListView) findViewById(R.id.custListView);
lv.setAdapter(adapter);
lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
startActivity(new Intent(CustomerView.this , EditCustomers.class));
}
});
Logcat显示它在我尝试删除项目时在73时崩溃。
09-10 20:54:25.497 6153-6153/mbl402.phoenix.edu.week4appni4992 E/AndroidRuntime: FATAL EXCEPTION: main
Process: mbl402.phoenix.edu.week4appni4992, PID: 6153
java.lang.NullPointerException: Attempt to invoke virtual method 'int android.database.sqlite.SQLiteDatabase.delete(java.lang.String, java.lang.String, java.lang.String[])' on a null object reference
at mbl402.phoenix.edu.week4appni4992.EditCustomers$2.onClick(EditCustomers.java:73)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
--------- beginning of system
public boolean UpdateData(String ID, String First, String Last, String MAKE, String MODEL, String Cost) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues cv = new ContentValues();
cv.put(CUSTOMER_FIRST_NAME, First);
cv.put(CUSTOMER_LAST_NAME, Last);
cv.put(CAR_MAKE, MAKE);
cv.put(CAR_MODEL, MODEL);
cv.put(COST, Cost);
db.update(Table_name, cv, "ID = ?", new String[]{ID});
return true;
}
public Integer deleteData(String ID) {
SQLiteDatabase db = this.getWritableDatabase();
return db.delete(Table_name, "ID =?", new String[]{ID});
}
这就是我用来完成类似项目的东西
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我来说两句