Android 使用McClickListener从ListView和数据库中删除项
我创建了一个数据库,并设法将添加的项目显示到列表视图中。现在我需要一个方法从ListView和数据库中删除一个项Android 使用McClickListener从ListView和数据库中删除项,android,sqlite,listview,android-sqlite,Android,Sqlite,Listview,Android Sqlite,我创建了一个数据库,并设法将添加的项目显示到列表视图中。现在我需要一个方法从ListView和数据库中删除一个项 public class ZeigeFaecherListe extends AppCompatActivity { DatabaseHelper myDb; @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(sav
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) {
}
});
}
}
公共类ZeigeFaecherListe扩展了AppCompative活动{
数据库助手myDb;
@凌驾
创建时受保护的void(@Nullable Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.zeige_faecher);
myDb=新数据库助手(此);
ListView listViewFaecher=(ListView)findViewById(R.id.listViewFaecher);
最终ArrayList FaecherList=新ArrayList();
Cursor res=myDb.zeigeFaecher();
如果(res.getCount()==0){
Toast.makeText(ZeigeFaecherListe.this,“Keine Fächer gefunden”,Toast.LENGTH_LONG.show();
}否则{
while(res.moveToNext()){
faecherListe.add(res.getString(1));
ListAdapter fachListAdapter=新的ArrayAdapter(这个,android.R.layout.simple\u list\u item\u 1,faecherListe);
listViewFaecher.setAdapter(传真适配器);
}
}
listViewFaecher.setOnItemClickListener(新的AdapterView.OnItemClickListener(){
@凌驾
public void onItemClick(AdapterView AdapterView,视图视图,整型位置,长id){
}
});
}
}
listViewFaecher.setOnItemClickListener(新的AdapterView.OnItemClickListener(){
@凌驾
public void onItemClick(AdapterView AdapterView,视图视图,整型位置,长id){
//通过传递位置在此处调用delete方法
//位置将包含用户单击的项目的位置。
}
});
简而言之,您需要能够根据ListView可用的数据来区分要删除的行。如果从光标检索到的值作为第二列(即使用res.getString(1)提取的字符串),,且该值将是唯一的,则可以检索该值并将其用于删除
但是,有一些问题,使用ListAdapter
可能是不够的。还有其他适配器,例如提供更多功能的ArrayAdapter,更重要的是,还有一个notifyDatasetChanged
方法(该方法将刷新关联的ListView)
为游标的每次迭代创建一个新适配器是一种浪费。因此,适配器应该在循环之外创建,并且只创建一次
我建议在项目点击时删除太容易发生意外点击,而在项目长点击时删除则不太容易发生意外删除
如果将变量移动为类变量,则不必将它们声明为final
因此,基于上述情况,您可以:-
阵列适配器方法
- 在哪里
- TB001是设置为表名的常量字符串
- COL_TB001_DATA是第二列的列名
警告只有在第二列包含唯一数据时,上述解决方案才能正常工作,否则将删除多行
还有一个假设是删除有效,最好是:-
@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
}
注意由于\u 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是多行。否。您需要一种方法从数据库中删除该项,然后相应地更新ListView。是的,但是我需要一种方法来选择具有listview的项目,我不知道如何实现。请参阅传递给onItemClick
方法的最后一个参数您有id
参数,该参数用于此。用户如何删除项目?只要点击它?或者他们必须选择它,然后按下删除按钮?
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));
}
}
}
public int deleteRow(String col2) {
SQLiteDatabase db = this.getWritableDatabase();
return db.delete(TB001,COL_TB001_DATA + "=?",new String[]{col2});
}
@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
}
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;
}
});
}
}