BaseAdapter class
(1) Overview
AdapterView fills data to the subclass view of AdapterView through Adapter (adapter class), among which, BaseAdapter is the base class of all adapter classes. This class is an abstract class
(2) Common methods
1、public View getView(int position,View convertView,ViewGroup
parent)
Role: Create and return list items, including the display style and data of list items,
Android draws list items based on the object returned by getView.
illustrate:
The first parameter -position: the index value of the current list item in the list
The second parameter -convertView: the View object of the current list item
The third parameter -parent: the parent container object of the list item - a list object
Hint: This method is an abstract method.
Example: The following code creates a label object and returns the object as a list item
@Override
public View getView(int position,View convertView,ViewGroup
parent){
//Instantiate the label object
TextView tvCityName = (TextView) findViewById
(R.layout.listview_item);
/ / Set the title of the label to the index value of the array in the position (that is, the current list item's
index value) element
tvCityName.setText(mCityName[position]);
return tvCityName; //return the label object
}
2、public long getItemId(int position)
Role: Returns the index value of the current list item
Parameter -position: the index value of the current list item
Hint: This method is an abstract method
Sample code:
@Override
public long getItemId(int position){
return postion;
}
3、public Object getItem(int position）
Role: Returns the current list item object
Parameter -position: the index value of the current list item
Hint: This method is an abstract method
Sample code:
@Override
public String getItem(int position){
return mCityName[position];
}
illustrate:
1. mCityName is an array of strings. The above code returns one of the array
element.
2. The default getItem returns the Object type, which should be modified in actual programming
is the specific type to be returned.
For example: In this example the returned type is String. If it is not modified, when calling this method, you need to do
Type conversion.
4、public int getCount()
Function: Returns the total number of objects in the list, the Android system returns according to getCount()
The returned value draws the specified number of list items.
Hint: This method is an abstract method.
Specific examples:
package com.jxust.day_05_01_listviewdemo;
import java.util.ArrayList;
import java.util.List;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
public class MainActivity extends Activity {
ListView mlvGeneral;
List<GeneralBean> mGenerals; // Represents a collection of ten military strategists
GeneralAdapter mAdapter;
int[] resid = { R.drawable.baiqi, R.drawable.caocao, R.drawable.chengjisihan, R.drawable.hanxin, R.drawable.lishimin, R.drawable.nuerhachi,
R.drawable.sunbin, R.drawable.sunwu, R.drawable.yuefei, R.drawable.zhuyuanzhang };
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate (savedInstanceState);
setContentView(R.layout.activity_main);
initData(); // initialize data
initView();
}
private void initView() {
mlvGeneral = (ListView) findViewById(R.id.lvGeneral);
mAdapter = new GeneralAdapter(); //Create an adapter
// Associate with ListView
mlvGeneral.setAdapter(mAdapter);
}
private void initData() {
// Convert the string array in the resource to a Java array
String[] names = getResources().getStringArray(R.array.generals);
mGenerals = new ArrayList<GeneralBean>();
for (int i = 0; i < names.length; i++) {
GeneralBean bean = new GeneralBean(resid[i], names[i]);
mGenerals.add(bean);
}
}
// Define the adapter class that represents the military strategist
class GeneralAdapter extends BaseAdapter {
@Override
public int getCount() {
return mGenerals.size();
}
@Override
public Object getItem(int position) {
return position;
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
// Get the layout of the ListView and convert it to an object of type View
View layout = View.inflate(MainActivity.this, R.layout.item_generals, null); // root represents the parent container
// Find the ImageView that displays the fighter's avatar
// The role of layout is to convert the target to layout.item_generals
ImageView ivThumb = (ImageView) layout.findViewById(R.id.ivThumb);
// Find the TextView that displays the military strategist's name
TextView tvName = (TextView) layout.findViewById(R.id.tvName);
// Get the strategist object whose subscript is position in the strategist
GeneralBean bean = mGenerals.get(position);
// Display the fighter's avatar
ivThumb.setImageResource(bean.getResid());
// Display the military strategist's name
tvName.setText(bean.getName());
return layout;
}
}
}
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<ListView
android:id="@+id/lvGeneral"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:divider="#ccc"
android:dividerHeight="2dp"
android:entries="@array/generals" />
</RelativeLayout>
<?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="wrap_content"
android:orientation="horizontal" >
<ImageView
android:id="@+id/ivThumb"
android:layout_width="80dp"
android:layout_height="80dp"
android:src="@drawable/baiqi"
/>
<TextView
android:id="@+id/tvName"
android:layout_width="wrap_content"
android:layout_height="80dp"
android:layout_marginLeft="10dp"
android:text="白起"
android:textSize="20sp"
android:gravity="center_vertical"
/>
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="app_name">Day_05_01_ListViewDemo</string>
<string name="hello_world">Hello world!</string>
<string name="action_settings">Settings</string>
<string-array name="generals">
<item >白起</item>
<item >曹操</item>
<item >Genghis Khan</item>
<item>Han Xin</item>
<item >Li Shimin</item>
<item >Nurhaci</item>
<item >孙膑</item>
<item >Sun Wu</item>
<item >Yue Fei</item>
<item >Zhu Yuanzhang</item>
</string-array>
</resources>