我创建了一个数据库并设法将添加的项目显示到ListView中。现在我需要一种从ListView和数据库中删除项目的方法。
public class ZeigeFaecherListe extends AppCompatActivity {
DatabaseHelper myDb;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.zeige_faecher);
myDb = new DatabaseHelper(this);
ListView listViewFaecher = (ListView) findViewById(R.id.listViewFaecher);
final ArrayList<String> faecherListe = new ArrayList<>();
Cursor res = myDb.zeigeFaecher();
if (res.getCount() == 0){
Toast.makeText(ZeigeFaecherListe.this, "Keine Fächer gefunden", Toast.LENGTH_LONG).show();
} else {
while (res.moveToNext()){
faecherListe.add(res.getString(1));
ListAdapter fachListAdapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, faecherListe);
listViewFaecher.setAdapter(fachListAdapter);
}
}
listViewFaecher.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {
}
});
}
}
答案 0 :(得分:1)
简而言之,您需要能够通过ListView可用的数据区分要删除的行。如果从游标中检索到的值,作为第二列(即使用res.getString(1))
提取的字符串,,并且该值将是唯一的,则可以检索此值并将其用于删除。
但是,有一些问题,使用ListAdapter
可能还不够。还有其他适配器,例如提供更多功能的ArrayAdapter,重要的是 notifyDatasetChanged
方法(将刷新关联的ListView)。
为游标的每次迭代创建一个新的适配器是一种浪费。所以适配器应该在循环之外创建,只需要创建一次。
我建议删除项目点击将太容易意外点击,删除项目LongClick将不太容易被意外删除。
如果将变量移动为类变量,则不必将它们声明为最终变量。
基于以上所述,您可以: -
public class ZeigeFaecherListe extends AppCompatActivity {
DatabaseHelper myDb;
Cursor res;
ListView listViewFaecher;
ArrayAdapter<String> fachListAdapter;
ArrayList<String> faecherListe;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.zeige_faecher);
listViewFaecher = (ListView) this.findViewById(R.id.listview);
myDb = new DatabaseHelper(this);
addSomeData(); //<<<<<<<<<< ADDED for testing
faecherListe = new ArrayList<>();
res = myDb.zeigeFaecher();
while (res.moveToNext()) {
faecherListe.add(res.getString(1));
}
//<<<< NOTE outside of the loop as this only needs to be done once
fachListAdapter = new ArrayAdapter<String>(
this,
android.R.layout.simple_list_item_1,
faecherListe
);
listViewFaecher.setAdapter(fachListAdapter);
//<<<<< NOTE used LONG CLICK listener (less likely to accidentally delete)
listViewFaecher.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
@Override
public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {
myDb.deleteRow((String)fachListAdapter.getItem(position));
faecherListe.remove(position);
fachListAdapter.notifyDataSetChanged();
return true; //<<<< Indicate that this longclick has been used
}
});
}
private void addSomeData() {
for (int i=1; i <= 10; i++) {
myDb.addRow("Row " + String.valueOf(i));
}
}
}
除此之外, deletRow
方法是: -
public int deleteRow(String col2) {
SQLiteDatabase db = this.getWritableDatabase();
return db.delete(TB001,COL_TB001_DATA + "=?",new String[]{col2});
}
警告上述解决方案仅在第二列包含唯一数据时才能正常工作,否则将删除多行。
还有一个假设是删除有效,最好有: -
@Override
public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {
if (myDb.deleteRow((String)fachListAdapter.getItem(position))<0) {
faecherListe.remove(position);
}
fachListAdapter.notifyDataSetChanged();
return true; //<<<< Indicate that this longclick has been used
}
但是,还有其他适合游标的适配器可以消除对中间阵列的需求。您可以使用 CursorAdapter
。对于 CursorAdapter
,列名称 _id
是必需的,此列应为长,并且还无法识别行。意图和名称是使用 rowid 的别名(因此也存在CONSTANT BaseColumns._ID
的原因。)
rowid 的别名是通过定义?? INTEGER PRIMARY KEY
来创建的?是列名。理想情况下,应该定义表格,包括使用_id INTEGER PRIMARY KEY
的列定义,例如CREATE mytable (_id INTEGER PRIMARY KEY, myothercolumn TEXT)
(您可以使用关键字AUTOINCREMENT关注INTEGER PRIMARY KEY
,但通常您不会这样做,因为它有开销SQLite Autoincrement)
如果您的表没有这样的列,那么您可以在查询数据时始终使用rowid AS _id
创建一个列。如果SQL等于SELECT * FROM mytable
,那么您可以使用SELECT *, rowid AS _id FROM mytable
。
在此示例中,将使用股票 SimpleCursorAdapter
,代码可以是: -
public class ZeigeFaecherListe extends AppCompatActivity {
DatabaseHelper myDb;
Cursor res;
ListView listViewFaecher;
SimpleCursorAdapter fachSimpleCursorAdapter;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.zeige_faecher);
listViewFaecher = (ListView) this.findViewById(R.id.listview);
myDb = new DatabaseHelper(this);
addSomeData(); //<<<<<<<<<< ADDED for testing
faecherListe = new ArrayList<>();
res = myDb.zeigeFaecher();
fachSimpleCursorAdapter = new SimpleCursorAdapter(this,
android.R.layout.simple_list_item_1, //<<<< The layout
res, //<<<< The Cursor
new String[]{"_data"}, //<<<< The column names from which to get the data
new int[]{android.R.id.text1} //<<<< The ids of the views in which the data is placed
);
listViewFaecher.setAdapter(fachSimpleCursorAdapter);
listViewFaecher.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
@Override
public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {
// id is the value of the respective _id column
//<<<< Normally you would have the delete method in the Databasehelper >>>>
myDb.getWritableDatabase().delete("mytable","_id=?",new String[]{String.valueOf(id)});
fachSimpleCursorAdapter.swapCursor(myDb.zeigeFaecher()); // Tell the adapter about the new cursor
return true;
}
});
}
}
注意,因为 _id
列始终是唯一的,如果显示的值不唯一,此方法将仅删除特定行而不删除多行。< / p>
答案 1 :(得分:-1)
listViewFaecher.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {
// Call delete method here by passing position
//position will contain the position of item clicked by the user.
}
});