轮播图的实现网上有很多资源,写这篇文章只是回顾所学的知识。对ViewPager的一些处理,比如适配器各个方法的作用等。
布局:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="so.wih.android.lunbotu.MainActivity">
<android.support.v4.view.ViewPager
android:id="@+id/view_pager"
android:layout_width="match_parent"
android:layout_height="200dp"
/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="50dp"
android:layout_alignBottom="@id/view_pager"
android:background="#aa000000"
android:gravity="center"
android:orientation="vertical">
<TextView
android:id="@+id/tv_desc"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:maxLines="1"
android:textColor="#FFFFFF"
android:textSize="16sp"
android:text="图片下的描述文字"/>
<LinearLayout
android:id="@+id/ll_point"
android:paddingTop="10dp"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal">
<!--这是指示点的位置-->
</LinearLayout>
</LinearLayout>
</RelativeLayout>
选择器:selector_point.xml
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item android:state_enabled="true" android:drawable="@drawable/point_select"></item>
<item android:drawable="@drawable/point_nomal"></item>
</selector>
point_nomal.xml
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="oval">
<size android:height="5dp" android:width="5dp"></size>
<solid android:color="#ccc"></solid>
</shape>
point_select.xml
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="oval">
<size android:width="5dp" android:height="5dp" ></size>
<solid android:color="#F00"></solid>
</shape>
代码(包含详细注释):
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
/**
* 图片资源id
*/
private final int[] imageIds = {R.mipmap.a,R.mipmap.b,R.mipmap.c,R.mipmap.d,R.mipmap.e};
/**
* 图片下的描述
*/
private final String[] desc = {"巩俐不低俗,我就不能低俗","扑树又回来啦!再唱经典老歌引万人大合唱"
,"揭秘北京电影如何升级","乐视网TV版大派送","热血屌丝的反杀"};
public List<ImageView> imageList = new ArrayList<>();
private ViewPager viewPager;
private TextView tv_desc;
private android.content.Context mContext;
private LinearLayout ll_point;
private ImageView iv_test;
/**
* 是否在运行程序
*/
private boolean isRunning = false;
//利用handler实现轮播
private Handler handler = new Handler(){
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
//检查消息队列并移除未发送的消息,这主要是避免在复杂环境下消息出现重复等问题。
if (handler.hasMessages(101)){
handler.removeMessages(101);
}
if(isRunning){
viewPager.setCurrentItem(viewPager.getCurrentItem()+1);
//形成循环2s发送消息,轮播
sendEmptyMessageDelayed(101,2000);
}
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mContext=this ;
setContentView(R.layout.activity_main);
viewPager = (ViewPager) findViewById(R.id.view_pager);
tv_desc = (TextView) findViewById(R.id.tv_desc);
ll_point = (LinearLayout) findViewById(R.id.ll_point);
//数据
for (int i=0;i<imageIds.length;i++){
//设置图片
ImageView iv_pic = new ImageView(mContext);
iv_pic.setBackgroundResource(imageIds[i]);
imageList.add(iv_pic);
//动态生成指示点
ImageView iv_point = new ImageView(mContext);
iv_point.setBackgroundResource(R.drawable.selector_point);
//生成布局参数
LinearLayout.LayoutParams param = new LinearLayout.LayoutParams(
LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT
);
//设置布局参数的margin值
param.leftMargin = 5 ;
//添加view时,传入布局参数
ll_point.addView(iv_point , param);
//处理初始时指示点的问题
if(i==0){
iv_point.setEnabled(true);
}else{
iv_point.setEnabled(false);
}
}
viewPager.setAdapter(new MyPagerAdapter());
/*
Integer.MAX_VALUE / 2 - Integer.MAX_VALUE / 2 % imageList.size()这个式子的结果是imageList.size()
的整数倍,即总是定位到下标为0的图片
*/
viewPager.setCurrentItem(Integer.MAX_VALUE / 2 - Integer.MAX_VALUE / 2 % imageList.size());
//初始时处理图片下的描述文字问题
tv_desc.setText(desc[0]);
isRunning = true ;
handler.sendEmptyMessageDelayed(101,2000); //2s后发送消息
initListener();
}
private class MyPagerAdapter extends PagerAdapter {
/**
* 获取所有Pager的总数
* @return
*/
@Override
public int getCount() {
return Integer.MAX_VALUE;
}
/**
* 判断view是否和object一致
* @param view
* @param object
* @return
*/
@Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
//还有两个方法,必须重写
/**
* 初始化页面
* @param container 容器
* @param position 范围0-2的32次方
* @return 返回值是一个View
*/
@Override
public Object instantiateItem(ViewGroup container, int position) {
//修改position的范围为0-(imageList.size()-1)
int _position = position % imageList.size();
ImageView iv_po = imageList.get(_position);
container.addView(iv_po);
return iv_po;
}
/**
* 销毁页面
* @param container
* @param position
* @param object
*/
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
//super.destroyItem(container, position, object);必须删掉此句,他在源码中直接抛出异常
container.removeView((View) object);
}
}
private void initListener() {
//添加页面改变监听
viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
int lastPosition = 0 ;
//当pager滑动的时候调用
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
//当页面被选中的时候调用
@Override
public void onPageSelected(int position) {
int _position = position % imageList.size();
tv_desc.setText(desc[_position]);
//设置上一个点不可用
ll_point.getChildAt(lastPosition).setEnabled(false);
//下一个点可用
ll_point.getChildAt(_position).setEnabled(true);
lastPosition = _position ;
}
//当pager滑动改变的时候调用
@Override
public void onPageScrollStateChanged(int state) {
}
});
}
//在退出时终止handler
@Override
protected void onDestroy() {
super.onDestroy();
isRunning = false ;
}
}