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ListView效率的提高

程序员文章站 2022-06-17 18:52:12
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Android开发时,当用ListView显示列表化内容,似乎并不能实现下拉显示后面更多的内容,或者之后的内容要开辟新的ListView,先前的不能重复利用,浪费资源,此处用BaseAdapter解决此问题:

此处,用显示简易的书籍列表做样例

先定义book类

public class Book {
	private String name,anthor;
	private double price;
	public Book() {
		super();
		// TODO Auto-generated constructor stub
	}
	public Book(String name, String anthor, double price) {
		super();
		this.name = name;
		this.anthor = anthor;
		this.price = price;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getAnthor() {
		return anthor;
	}
	public void setAnthor(String anthor) {
		this.anthor = anthor;
	}
	public double getPrice() {
		return price;
	}
	public void setPrice(double price) {
		this.price = price;
	}

}


//导入各种包
public class Anli extends Activity {
	List<Book> booklist =new ArrayList<Book>(); 
	ListView list;
	
	void fill()//填入各种书籍名称,这里随便
	{
		booklist.add(new Book("C语言","啦啦啦",23));
		booklist.add(new Book("CC语言","啦啦啦",25));
		booklist.add(new Book("CCC语言","啦啦啦",243));
	}
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.anli);
		
		fill();
		
		list=(ListView)findViewById(R.id.listbook);
		list.setAdapter(new MyAdapter());//设置适配器
	
	}
	class MyAdapter extends BaseAdapter
	{

		@Override
		public int getCount() {
			// TODO Auto-generated method stub
			return booklist.size();
		}

		@Override
		public Object getItem(int position) {
			// TODO Auto-generated method stub
			return position;
		}

		@Override
		public long getItemId(int position) {
			// TODO Auto-generated method stub
			return position;
		}

		@Override   //重写getView方法
		public View getView(int position, View convertView, ViewGroup parent) {
			View row= convertView;
			Wrapper www = null;
			
			if(row==null)
			{
				//如果为空,做解析,不能直接用
				row=LayoutInflater.from(Anli.this).inflate(R.layout.anli2, parent, false);
				//将布局文件解析为view好资源,如果不为空,就不解析,重复利用
				www=new Wrapper(row);
				row.setTag(www);
			}
			else
			{
				www=(Wrapper)row.getTag();
			}
			
				
			//会重复,要修改
			TextView bookname=www.getBookname();
			TextView bookanthor=www.getBookauthor();
			TextView bookprice=www.getBookprice();
			
			Book book=booklist.get(position);
			
			bookname.setText(book.getName());
			bookanthor.setText(book.getAnthor());
			bookprice.setText(book.getPrice()+"");
			return row;
		}
		
	}//MyAdapter
	
	class Wrapper
	{
		TextView bookname;
		TextView bookanthor;
		TextView bookprice;
		View row;
		public Wrapper(View row)
		{
			this.row=row;
		}
		
		public TextView getBookname()
		{
			if(bookname==null)
			{
				//如果为空,查找
				TextView bookname=(TextView) row.findViewById(R.id.bookname);
			}
			return bookname;
		}
		public TextView getBookauthor()
		{
			if(bookanthor==null)
			{
				//如果为空,查找
				TextView bookanthor=(TextView) row.findViewById(R.id.bookauthor);
			}
			return bookanthor;
		}
		public TextView getBookprice()
		{
			if(bookprice==null)
			{
				//如果为空,查找
				TextView bookprice=(TextView) row.findViewById(R.id.bookpricec);
			}
			return bookprice;
		}
	}//wrapper
	
	
}