abstract：ListView就是用來顯示一行一行的條目的MVC結(jié)構(gòu) * M：model模型層，要顯示的數(shù)據(jù) ————people集合 * V：view視圖層，用戶看到的界面 &n
ListView
就是用來顯示一行一行的條目的
MVC結(jié)構(gòu)
* M：model模型層，要顯示的數(shù)據(jù) ————people集合
* V：view視圖層，用戶看到的界面 ————ListView
* c：control控制層，操作數(shù)據(jù)如何顯示 ————adapter對象
每一個條目都是一個View對象
BaseAdapter
* 必須實(shí)現(xiàn)的兩個方法
* 第一個
//系統(tǒng)調(diào)用此方法，用來獲知模型層有多少條數(shù)據(jù)
@Override
public int getCount() {
return people.size();
}
* 第二個
//系統(tǒng)調(diào)用此方法，獲取要顯示至ListView的View對象
//position:是return的View對象所對應(yīng)的數(shù)據(jù)在集合中的位置
@Override
public View getView(int position, View convertView, ViewGroup parent) {
System.out.println("getView方法調(diào)用" + position);
TextView tv = new TextView(MainActivity.this);
//拿到集合中的元素
Person p = people.get(position);
tv.setText(p.toString());
//把TextView的對象返回出去，它會變成ListView的條目
return tv;
}
屏幕上能顯示多少個條目，getView方法就會被調(diào)用多少次，屏幕向下滑動時，getView會繼續(xù)被調(diào)用，創(chuàng)建更多的View對象顯示至屏幕
條目的緩存
當(dāng)條目劃出屏幕時，系統(tǒng)會把該條目緩存至內(nèi)存，當(dāng)該條目再次進(jìn)入屏幕，系統(tǒng)在重新調(diào)用getView時會把緩存的條目作為convertView參數(shù)傳入，但是傳入的條目不一定是之前被緩存的該條目，即系統(tǒng)有可能在調(diào)用getView方法獲取第一個條目時，傳入任意一個條目的緩存
代碼如下：
activity_main.xml:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" tools:context="com.example.list.MainActivity" > <ListView android:id="@+id/lv" android:layout_width="fill_parent" android:layout_height="fill_parent" ></ListView> </LinearLayout>
item.xml
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" > <ImageView android:id="@+id/iv" android:src="@drawable/xing" android:layout_width="80dp" android:layout_height="80dp" /> <TextView android:id="@+id/t1" android:layout_width="match_parent" android:layout_height="wrap_content" /> <TextView android:id="@+id/t2" android:layout_width="match_parent" android:layout_height="wrap_content" /> </LinearLayout>
MainActivity.java
public class MainActivity extends Activity {
List<shopInfo> l;
ListView lv;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
lv = (ListView) findViewById(R.id.lv);
//準(zhǔn)備集合數(shù)據(jù)
l = new ArrayList<shopInfo>();
l.add(new shopInfo(R.drawable.xing, "name-1", "content-1"));
l.add(new shopInfo(R.drawable.xing, "name-2", "content-2"));
l.add(new shopInfo(R.drawable.xing, "name-3", "content-3"));
l.add(new shopInfo(R.drawable.xing, "name-4", "content-4"));
l.add(new shopInfo(R.drawable.xing, "name-5", "content-5"));
l.add(new shopInfo(R.drawable.xing, "name-6", "content-6"));
l.add(new shopInfo(R.drawable.xing, "name-7", "content-7"));
l.add(new shopInfo(R.drawable.xing, "name-8", "content-8"));
//準(zhǔn)備BaseAdapter對象
MyAdapter a = new MyAdapter();
//設(shè)置Adapter顯示數(shù)據(jù)
lv.setAdapter(a);
}
//這個類可以寫在里面，也可以寫在外面
public class MyAdapter extends BaseAdapter {
@Override
public int getCount() {
// TODO Auto-generated method stub
return l.size();
}
@Override
public Object getItem(int arg0) {
// TODO Auto-generated method stub
return null;
}
@Override
public long getItemId(int arg0) {
// TODO Auto-generated method stub
return 0;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
// TODO Auto-generated method stub
// 加載item的布局
View view = View.inflate(MainActivity.this, R.layout.item, null);
shopInfo s = l.get(position);
ImageView i = (ImageView) view.findViewById(R.id.iv);
TextView t1 = (TextView) view.findViewById(R.id.t1);
TextView t2 = (TextView) view.findViewById(R.id.t2);
i.setImageResource(s.getIcon());
t1.setText(s.getName());
t2.setText(s.getContent());
convertView = view ;
return convertView;
}
}
}shopInfo.java
//每行item的數(shù)據(jù)信息封裝類
public class shopInfo {
private int icon;
private String name;
private String content;
public int getIcon() {
return icon;
}
public void setIcon(int icon) {
this.icon = icon;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
public shopInfo(int icon, String name, String content) {
super();
this.icon = icon;
this.name = name;
this.content = content;
}
@Override
public String toString() {
return "shopInfo [icon=" + icon + ", name=" + name + ", content="
+ content + "]";
}
public shopInfo() {
super();
// TODO Auto-generated constructor stub
}
}