如何将数据添加到listviewAdapter？

Question

我已经制作了listViewAdapter，它从三个EditText中获取数据并在其上显示，但问题是，如果我点击添加按钮，那么第一个条目将由新条目覆盖。我想要添加数据在列表。

这是我的android代码：

 public class List extends AppCompatActivity {

private EditText etItem;
private EditText etQty;
private EditText etRate;

public static String item;
public static String qty;
public static String rate;
private ArrayList<HashMap> list;
public listviewAdapter adapter;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_list);

    etItem=(EditText)findViewById(R.id.etItem);
    etQty=(EditText)findViewById(R.id.etQty);
    etRate=(EditText)findViewById(R.id.etRate);

    item=etItem.getText().toString();
    qty=etQty.getText().toString();
    rate=etRate.getText().toString();



    Button bAdd=(Button)findViewById(R.id.bAdd);
    bAdd.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            ListView lview = (ListView) findViewById(R.id.listview);
            populateList();
            listviewAdapter adapter = new listviewAdapter(List.this, list);
            lview.setAdapter(adapter);
            adapter.notifyDataSetChanged();
            etItem.setText("");
            etQty.setText("");
            etRate.setText("");
        }
    });
}
private void populateList() {
    list = new ArrayList<HashMap>();
    item=etItem.getText().toString();
    qty=etQty.getText().toString();
    rate=etRate.getText().toString();
    HashMap temp = new HashMap();

    temp.put(FIRST_COLUMN,"");
    temp.put(SECOND_COLUMN, item);
    temp.put(THIRD_COLUMN, qty);
    temp.put(FOURTH_COLUMN, rate);
    list.add(temp);
}

Answer 1

您必须使所有可重用参数必须全局。全局生成ListView对象和Adapter Class对象以及List数据，不要使用新构造函数重新赋值。在onCreate方法上添加以下代码并从重新赋值中删除。

ListView lview;
listviewAdapter adapter;

onCreate方法中的

lview = (ListView) findViewById(R.id.listview);
list = new ArrayList<HashMap>();
adapter = new listviewAdapter(List.this, list);
lview.setAdapter(adapter);

现在在populateList（）方法中添加三个参数，如

populateList(String item,String qty,String rate)

现在使用

从Button onClick事件添加数据

item=etItem.getText().toString();
qty=etQty.getText().toString();
rate=etRate.getText().toString();
populateList(item,qty,rate);

并调用notifyDataSetChange来刷新适配器和ListView，在populateList方法的最后一行添加它

adapter.notifyDataSetChanged();

Answer 2

将hashmap打包到列表（适配器）是一个不可见的:)

1）创建简单的pojo

https://en.wikipedia.org/wiki/Plain_Old_Java_Object

public class Item {
      private String _itemName;
      private int _qty;
      private int _rate;

     public Item(String itemName, int qty, int rate) {
         _itemName = itemName;
         _qty = qty;
         _rate = rate;
     }

     // create getter/setter if need 

    public String getName() { return _itemName;}
    // if you want create setter 
    // then keep in mind your 
    // item _itemName variable could not be marked as final 
    public void setName(String name) { _itemName = name;} 
}

2）创建适配器扩展，例如BaseAdapter类     https://developer.android.com/reference/android/widget/BaseAdapter.html

public class MyAdapter extends BaseAdapter {

    private List<item> _myList;

   public MyAdapter(Context context, List<Item> myList) {
         // context is useful to use for create an inflater and getView method
         _context = context;  
         // check on list here 
         // instantiate new if need (if you plane to use method on list) 
         // to avoid null pointer exceptions 
        _myList = myList;
   }
       // implement rest methods methods for base adapter 
       //  getView() , id etc 
       // implement methods to add delete clear (on list) 


      public void addItem(Item item) {
         // do some chcks on list is not empty etc 
          _myList.add(item);
        // notify adapter observers to update their states
        notifyDatasetChanged();
      }
}

3）使用带列表视图的适配器：

  // create list to hold items 
  List<Items> listItems = new ArrayList<>()
  // create item 1
  Item item1 = new Item(String,int,int);
  // add item 1
  listItems.add(item1);
  Item item2 = new Item(String,int,int);
  listItems.add(item2)
  // create adapter 
  MyAdapter myAdapter = new MyAdapter(Context, listItems) 
  //set adapter 
  listView.setAdapter(myAdapter);

 // later you can re-user adapter 
 Adapter adapter = listView.getAdapter() 
 if(adapter !=- null && MyAdapter.class.isAssingableFromClass(adapter.getClass) {
     // do cast 
     MyAdapter myAdapter = MyAdapter(adapter);
     // add new item 
     myAdapter.addItem( new Item (...););
} 

完整示例：

https://github.com/c3ph3us/examples/blob/master/VaultListAdapter.java

其他示例和信息：

• http://abhiandroid.com/ui/baseadapter-tutorial-example.html
• http://androidadapternotifiydatasetchanged.blogspot.com/
• How to customize listview using baseadapter

如果你只是加载一个简单的对象列表，那么ArrayAdapter比BaseAdapter更受欢迎 - cricket_007

您的意思是使用还是延长？

ArrayAdapter：

  

由任意对象数组支持的具体BaseAdapter。 默认情况下，此类要求提供的资源ID引用单个TextView 。如果要使用更复杂的布局，请使用也带有字段ID的构造函数。该字段id应引用较大布局资源中的TextView。

1. 我认为没有任何意义需要在这里利用更多资源

2. 在我看来，使用更复杂的类/库不会让你学习语言 - 你应该使用低级方法来获得新技能

Answer 3

我希望这会对你有所帮助：

在onCreate（）

中执行此操作

           cross = (ImageButton) findViewById(R.id.cross);

       lview = (ListView) findViewById(R.id.listview);
       lview.setItemsCanFocus(false);


       clicks();
       }

然后添加此方法：

     private void populateList() {
       HashMap temp = new HashMap();
       list = new ArrayList<HashMap>();

       item = etItem.getText().toString();
       qty = etQty.getText().toString();
       rate = etRate.getText().toString();

       temp.put(FIRST_COLUMN, "1");
       temp.put(SECOND_COLUMN, item);
       temp.put(THIRD_COLUMN, qty);
       temp.put(FOURTH_COLUMN, rate);
       list.add(temp);


   }

   private void populateList1() {
       HashMap temp1 = new HashMap();

       i++;
       sno = Integer.toString(i);
       item = etItem.getText().toString();
       qty = etQty.getText().toString();
       rate = etRate.getText().toString();


       temp1.put(FIRST_COLUMN, sno);
       temp1.put(SECOND_COLUMN, item);
       temp1.put(THIRD_COLUMN, qty);
       temp1.put(FOURTH_COLUMN, rate);
       list.add(temp1);
       adapter.notifyDataSetChanged();
   }

   public void clicks() {

       Button bAdd = (Button) findViewById(R.id.bAdd);
       bAdd.setOnClickListener(new View.OnClickListener() {
           @Override
           public void onClick(View v) {
               if (click == true) {
                   populateList();
                   adapter = new listviewAdapter(List.this, list);
                   lview.setAdapter(adapter);
                   etItem.setText("");
                   etQty.setText("");
                   etRate.setText("");
                   click = false;
               } else if (click == false) {
                   populateList1();
                   etItem.setText("");
                   etQty.setText("");
                   etRate.setText("");
               }
           }
       });

   }

希望我能帮助你:)。