深入ListView
深入ListView
我们接着上一篇博客，对ListView进行更加深入的了解。
属性
android:cacheColorHint=”@color/white” 设置ListView滚动时的背景色
android:divider=”@color/red” 设置ListView分割线的颜色
android:dividerHeight=”1dp” 设置ListView分割线的高度
设置点击列表的背景
更改listview点击背景与更改Button点击背景和RadioButton选择图标的方法类似。
①在drawable文件夹下新建xml文档list_background.xml
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android" >
<item android:drawable="@color/red" android:state_pressed="true"/>
<item android:drawable="@color/white"/>
</selector>②在自定义的布局中加入属性background
android:background="@drawable/list_background"提升ListView的运行效率
- 在上一篇博客中，StudentAdapter的getView()方法，每次都将布局重新加载了一遍，当ListView快速滚动的时候这就会成为性能的瓶颈。我们注意到getView()方法中还有一个参数convertView，这个参数用于将之前加载好的布局进行缓存，以便之后可以进行重用。
我们在getView()方法中进行了判断，如果convertView为空，则使用inflater去加载布局，如果不为空则直接对convertView进行重用。 - 我们每次在getView()方法中还是会调用View的findViewById()方法来获取一次控件的实例。此时可以借助一个ViewHolder来对这部分性能进行优化。
新增一个内部类ViewHolder，用于对控件的实例进行缓存。当convertView为空，创建一个ViewHolder对象，并将控件的实例都存放在ViewHolder里，然后调用View的setTag()方法，将ViewHolder对象存储在View中。当convertView不为空时则调用View的getTag()方法，将ViewHolder重新取出。
优化后的代码：
@Override
public View getView(int position, View convertView, ViewGroup parent) {
Stuent student = arraylist.get(position);
View view;
ViewHolder viewHolder;
if (convertView == null) {
view = inflater.inflate(R.layout.simpleadapter_layout, null);
viewHolder=new ViewHolder();
viewHolder.image = (ImageView) view.findViewById(R.id.imageview);
viewHolder.textview_name = (TextView) view.findViewById(R.id.textview_name);
viewHolder.textview_age = (TextView) view.findViewById(R.id.textview_age);
viewHolder.textview_sex = (TextView) view.findViewById(R.id.textview_sex);
viewHolder.textview_hobby = (TextView) view.findViewById(R.id.textview_hobby);
view.setTag(viewHolder);//将viewHolder存储在view中
}else{
view=convertView;
viewHolder=(ViewHolder) view.getTag();//重新获取viewHolder
}
viewHolder.textview_name.setText(student.getName());
viewHolder.textview_age.setText(student.getAge());
viewHolder.textview_sex.setText(student.getSex());
viewHolder.textview_hobby.setText(student.getHobby());
viewHolder.image.setImageResource(student.getImage());
return view;
}
class ViewHolder{
ImageView image;
TextView textview_name;
TextView textview_age;
TextView textview_sex;
TextView textview_hobby;
}ListView其他常见的用法
在ListView加入其他点击控件
当我们在ListView中加入了其他的点击控件，如CheckBox，Button，RadioButton等，就会抢夺ListView的焦点，这时我们点击ListView就没有反应。
我们有两种办法可以解决这个问题：
①在ListView中设置屏蔽子控件抢夺ListView的焦点
android:descendantFocusability="blocksDescendants" ②在子控件本身设置焦点属性为false。
android:focusable="false"添加HeaderView和FooterView
- 首先我们要新建HeaderView或FooterView的布局xml文件
- 然后用LayoutInflater加载布局，生成View对象
- 最后调用addHeaderView()或addFooterView()，传入View对象即可。
注意：当我们在ListView中添加了HeaderView之后，使用ListView点击事件时，ListView中item的索引要减1。
综合的代码示例
定义一个实体类 Fruit
public class Fruit {
private int image;
private String name;
private boolean isChecked;
public Fruit(int image, String name) {
this.image = image;
this.name = name;
}
public int getImage() {
return image;
}
public void setImage(int image) {
this.image = image;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public boolean isChecked() {
return isChecked;
}
public void setChecked(boolean isChecked) {
this.isChecked = isChecked;
}
}为listview的子项指定自定义的布局
?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="horizontal" >
<CheckBox android:id="@+id/checkbox" android:layout_width="wrap_content" android:layout_height="wrap_content" android:focusable="false" android:text="选择水果"/>
<ImageView android:id="@+id/fruit" android:layout_width="wrap_content" android:layout_height="wrap_content"/>
<TextView android:id="@+id/textview" android:layout_width="wrap_content" android:layout_height="wrap_content"/>
</LinearLayout>自定义适配器FruitAdapter.java
mport java.util.ArrayList;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.CompoundButton.OnCheckedChangeListener;
import android.widget.ImageView;
import android.widget.TextView;
public class FruitAdapter extends BaseAdapter {
private LayoutInflater inflater;
private ArrayList<Fruit> list;
public FruitAdapter(LayoutInflater inflater, ArrayList<Fruit> list) {
this.inflater = inflater;
this.list = list;
}
/** * 全选 */
public void checkAll() {
for (int i = 0; i < list.size(); i++) {
list.get(i).setChecked(true);
}
notifyDataSetChanged();
}
/** * 反选 */
public void reverse() {
for (int i = 0; i < list.size(); i++) {
selectItem(i);
}
}
/** * 点击ListView可以勾选住CheckBox * * @param position 当前ListView的位置 */
public void selectItem(int position) {
boolean isChecked = list.get(position).isChecked();
isChecked = !isChecked;
list.get(position).setChecked(isChecked);
notifyDataSetChanged();// 刷新界面
}
@Override
public int getCount() {
return list.size();
}
@Override
public Object getItem(int arg0) {
return arg0;
}
@Override
public long getItemId(int arg0) {
return arg0;
}
@Override
public View getView(final int position, View convertView, ViewGroup arg2) {
Fruit fruit = list.get(position);
View view;
ViewHolder viewHolder;
if (convertView == null) {
view = inflater.inflate(R.layout.fruit_layout, null);
viewHolder = new ViewHolder();
viewHolder.checkbox = (CheckBox) view.findViewById(R.id.checkbox);
viewHolder.image = (ImageView) view.findViewById(R.id.fruit);
viewHolder.name = (TextView) view.findViewById(R.id.textview);
view.setTag(viewHolder);
} else {
view = convertView;
viewHolder = (ViewHolder) view.getTag();
}
viewHolder.image.setImageResource(fruit.getImage());
viewHolder.name.setText(fruit.getName());
viewHolder.checkbox
.setOnCheckedChangeListener(new OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView,
boolean isChecked) {
list.get(position).setChecked(isChecked);//如果勾选，将该项设为true
}
});
viewHolder.checkbox.setChecked(fruit.isChecked());//将ViewHolder中的实例重新设置为false
return view;
}
class ViewHolder {
CheckBox checkbox;
ImageView image;
TextView name;
}
}HeaderView和FooterView的布局文件
<?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" >
<Button android:id="@+id/button_quan" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="全选"/>
</LinearLayout><?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" >
<Button android:id="@+id/button_fan" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="反选"/>
</LinearLayout>MainActivity
import java.util.ArrayList;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.Toast;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListView;
import android.app.Activity;
public class MainActivity extends Activity {
private LayoutInflater inflater;
private FruitAdapter adapter;
private ArrayList<Fruit> list;
private View fruitHeaderView;
private View fruitFooterView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
list = new ArrayList<Fruit>();
for (int i = 0; i < 5; i++) {
Fruit apple = new Fruit(R.drawable.apple, "苹果");
Fruit banana = new Fruit(R.drawable.banana, "香蕉");
Fruit grape = new Fruit(R.drawable.grape, "葡萄");
Fruit strawberry = new Fruit(R.drawable.strawberry, "草莓");
list.add(apple);
list.add(banana);
list.add(grape);
list.add(strawberry);
}
inflater = getLayoutInflater();
adapter = new FruitAdapter(inflater, list);
ListView listView = (ListView) findViewById(R.id.listview_fruit);
fruitHeaderView = inflater.inflate(R.layout.fruit_header, null);
listView.addHeaderView(fruitHeaderView);
Button button_quan = (Button) fruitHeaderView
.findViewById(R.id.button_quan);
button_quan.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
adapter.checkAll();// 全选
}
});
fruitFooterView = inflater.inflate(R.layout.fruit_footer, null);
listView.addFooterView(fruitFooterView);
Button button_fan = (Button) fruitFooterView
.findViewById(R.id.button_fan);
button_fan.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
adapter.reverse();// 反选
}
});
listView.setAdapter(adapter);
//点击listview，勾选中当前checkbox
listView.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View view,
int position, long id) {
// 因为加了HeaderView，所以索引要减1
adapter.selectItem(position - 1);// 调用点击lsitview选择checkbox的方法
Toast.makeText(MainActivity.this,
"选择的水果为：" + list.get(position - 1).getName(),
Toast.LENGTH_SHORT).show();
}
});
}
}运行结果：
点击ListView，会勾选CheckBox
点击全选，则全部选中
点击反选，则去掉之前选中的其余部分