【发布时间】：2019-11-22 16:23:29
【问题描述】：
我制作了一个简单的购物清单应用程序，用户可以在其中向列表视图添加商品。我的问题是当我离开应用程序时，项目不会保存。我认为我需要使用共享首选项，但没有太多看实现它（我对编码相当陌生）如果有人知道如何实现共享首选项以便我的项目将保存它，将不胜感激。
我的代码：
public class CreateAList extends AppCompatActivity {
//ArrayList for data
private ArrayList<String> list = new ArrayList<>();
ListView list_view;
ArrayAdapter arrayAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_create_alist);
//find view by id
list_view = findViewById(R.id.list_view);
arrayAdapter = new ArrayAdapter(CreateAList.this, android.R.layout.simple_list_item_1,list);
list_view.setAdapter(arrayAdapter);
list_view.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(final AdapterView<?> adapterView, View view, final int i, long l) {
//Inflating is the process of adding a view(.xml) to activity on runtime
PopupMenu popupMenu = new PopupMenu(CreateAList.this,view);
popupMenu.getMenuInflater().inflate(R.menu.pop_up_menu,popupMenu.getMenu());
popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
@Override
public boolean onMenuItemClick(MenuItem menuItem) {
switch (menuItem.getItemId()){
case R.id.item_update:
//function for update
AlertDialog.Builder builder = new AlertDialog.Builder(CreateAList.this);
View v = LayoutInflater.from(CreateAList.this).inflate(R.layout.item_dialog,null,false);
builder.setTitle("Update Item");
final EditText editText = v.findViewById(R.id.editItem);
editText.setText(list.get(i));
//set custom view to dialog
builder.setView(v);
builder.setPositiveButton("Update", new DialogInterface.OnClickListener(){
@Override
public void onClick(DialogInterface dialog, int which) {
if (!editText.getText().toString().isEmpty()){
list.set(i, editText.getText().toString().trim());
arrayAdapter.notifyDataSetChanged();
Toast.makeText(CreateAList.this, "Item Updated", Toast.LENGTH_SHORT).show();
}else{
editText.setError("add item here!");
}
}
});
builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int i) {
dialog.dismiss();
}
});
builder.show();
break;
case R.id.item_delete:
//function for delete
Toast.makeText(CreateAList.this, "Item Deleted", Toast.LENGTH_SHORT).show();
list.remove(i);
arrayAdapter.notifyDataSetChanged();
break;
}
return true;
}
});
popupMenu.show();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main_menu,menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()){
case R.id.add_item:
//function to add
addItem();
break;
}
return true;
}
//method for adding item
private void addItem() {
AlertDialog.Builder builder = new AlertDialog.Builder(CreateAList.this);
builder.setTitle("Add new Item");
View v = LayoutInflater.from(CreateAList.this).inflate(R.layout.item_dialog,null,false);
builder.setView(v);
final EditText editItem = v.findViewById(R.id.editItem);
builder.setPositiveButton("Add", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
if (!editItem.getText().toString().isEmpty()){
list.add(editItem.getText().toString().trim());
arrayAdapter.notifyDataSetChanged();
}else{
editItem.setError("Add Item Here!");
}
}
});
}
【问题讨论】：