Android BaseAdapter

BaseAdapter是Android应用程序中经常用到的基础数据适配器，其主要用途为将一组数据传递到ListView，Spinner，GridView等UI组件。BaseAdapter对于前面提到的三个UI组件来说是万能的，ListView、Spinner、GridView各自都有自己的适配器，但是BaseAdapter对于它们是通用的。比如我们经常使用的ListView的SimpleAdapter是继承自BaseAdapter的。

下面就来看一看BaseAdapter的用法：

使用BaseAdapter时，我们常写一个类来继承它。因为BaseAdapter是一个抽象类，所以要在类中实现它的方法。

public class MyAdapter extends BaseAdapter{
private Context context;
private List<String> listBase;

public MyAdapter(Context context,ArrayList<String> listBase){
this.context = context;
this.listBase = listBase;
}

@Override
public int getCount() {
return listBase.size();
}

@Override
public Object getItem(int i) {
return listBase.get(i);
}

@Override
public long getItemId(int i) {
return i;
}

@Override
public View getView(int i, View view, ViewGroup viewGroup) {
ViewHolder viewHolder;
if (view == null){
view = View.inflate(context,R.layout.list_item_view,null);
viewHolder = new ViewHolder();
viewHolder.textView = (TextView) view.findViewById(R.id.textView1);
view.setTag(viewHolder);
}else {
viewHolder = (ViewHolder) view.getTag();
}
viewHolder.textView.setText(listBase.get(i));
return view;
}

public class ViewHolder{
public TextView textView;
}
}

子项布局文件：

list_item_view.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">

<LinearLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content">

<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />

</LinearLayout>

</LinearLayout>

下面是整体代码：

MainActivity.java

public class MainActivity extends Activity {

ListView listView;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listView = (ListView) findViewById(R.id.list_view);
List<String> listData = new ArrayList<String>();
for (int i =0;i<100;i++){
listData.add("Item"+i);
}
listView.setAdapter(new MyAdapter(this, (ArrayList<String>) listData));
}

public class MyAdapter extends BaseAdapter{
private Context context;
private List<String> listBase;

public MyAdapter(Context context,ArrayList<String> listBase){
this.context = context;
this.listBase = listBase;
}

@Override
public int getCount() {
return listBase.size();
}

@Override
public Object getItem(int i) {
return listBase.get(i);
}

@Override
public long getItemId(int i) {
return i;
}

@Override
public View getView(int i, View view, ViewGroup viewGroup) {
ViewHolder viewHolder;
if (view == null){
view = View.inflate(context,R.layout.list_item_view,null);
viewHolder = new ViewHolder();
viewHolder.textView = (TextView) view.findViewById(R.id.textView1);
view.setTag(viewHolder);
}else {
viewHolder = (ViewHolder) view.getTag();
}
viewHolder.textView.setText(listBase.get(i));
return view;
}

public class ViewHolder{
public TextView textView;
}
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();

//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}

return super.onOptionsItemSelected(item);
}
}