Question

我正在学习getTag和setTag。我需要解释这些方法，并想知道它们是如何工作的。我创建了一个简单的CustomListView，它有两个按钮和一个textview。按钮是加减法，它增加或减少计数器的值，但问题是只有最后一个项值正在改变。请给我一个解决方案以及一个很好的解释谢谢。

@Override
    public View getView(int position, View convertView, ViewGroup parent) {

        if (convertView == null) {
            convertView = inflater.inflate(R.layout.list_items, null);
            add = (Button) convertView.findViewById(R.id.add);
            sub = (Button) convertView.findViewById(R.id.sub);
            textView = (TextView) convertView.findViewById(R.id.numberTV);
            convertView.setTag(new ViewHolder(add, sub, textView , count));
        }
        holder = (ViewHolder) convertView.getTag();
        textView = holder.textView;
        count = holder.counter;
        add = holder.add;
        sub = holder.sub;
        add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                count +=1;
                textView.setText(String.valueOf(count));
            }
        });
        sub.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                count -=1;
                textView.setText(String.valueOf(count));
            }
        });
        return convertView;
    }
}

class ViewHolder {

    Button add, sub;
    TextView textView;
int counter = 0;
    public ViewHolder(Button add, Button sub, TextView textView , int counter) {
        this.add = add;
        this.sub = sub;
        this.counter = counter;
        this.textView = textView;
    }
}

Answer 1

在custom listview adapter中，您要实施的内容是recycling中显示的single item (list_items) Listview。因此，您需要对该视图使用getTag和setTag方法。

那你为什么要首先要这些方法......

您正在尝试回收list_items并在其中查看，为此您正在制作ViewHolder，其中包含list_items内部视图的内部参考
您不想调用inflater并且每次调用getView时都会对视图进行引用，因此您将ViewHolder's实例保存到视图中，该视图将再次使用没有重新膨胀list_items及其中的引用。
按setTag()，您可以将对象附加到View
通过getTag()，您可以取回附加到View

因此，每次调用list_items时，您都会循环使用getView()的相同初始化

似乎做了很多工作，请使用RecyclerView。

您的代码解决方案......您可以查看gitHub

public class ListViewTestFiveActivity extends AppCompatActivity{

    private ListView listView;

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


        initializeUI();
    }

    private void initializeUI() {
        listView = (ListView)findViewById(R.id.ListViewTestFiveActivity_listView);
        ArrayList<Item> items = new ArrayList<>();

        for (int i = 0; i < 15; i++) {
            Item item = new Item();
            item.setCount(i);
            items.add(item);
        }

        MyAdapter adapter = new MyAdapter(getApplicationContext(), R.layout.single_item_listview_five, items);
        listView.setAdapter(adapter);
    }

    private class MyAdapter extends ArrayAdapter{

        private ArrayList<Item> items;
        private Context a_context;
        private LayoutInflater a_layoutInflater;

        public MyAdapter(Context context, int resource, ArrayList<Item> items) {
            super(context, resource, items);
            this.a_context = context;
            this.items = items;
            a_layoutInflater = LayoutInflater.from(this.a_context);
        }


        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            View row = convertView;
            ViewHolder holder = null;
            if (row == null) {
                row = a_layoutInflater.inflate(R.layout.single_item_listview_five, parent, false);
                holder = new ViewHolder();
                holder.plus = (Button) row.findViewById(R.id.ListViewTestFiveActivity_plus_button);
                holder.textView = (TextView) row.findViewById(R.id.ListViewTestFiveActivity_count_textView4);
                holder.minus = (Button) row.findViewById(R.id.ListViewTestFiveActivity_minus_button);
                row.setTag(holder);
            } else {
                holder = (ViewHolder) row.getTag();
            }

            final Item item = items.get(position);
            holder.textView.setText("" + item.getCount());
            holder.plus.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    int increase_count =item.getCount();
                    item.setCount(++increase_count);
                    notifyDataSetChanged();
                }
            });
            holder.minus.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    int decrease_count =item.getCount();
                    item.setCount(--decrease_count );
                    notifyDataSetChanged();
                }
            });
            return row;
        }

        private class ViewHolder{
            Button plus;
            TextView textView;
            TextView minus;
        }
    }

    private class Item {
        int count;

        public int getCount() {
            return count;
        }

        public void setCount(int count) {
            this.count = count;
        }
    }
}

输出

使用getTag和setTag来保存ListItem值

1 个答案: