Android实现轮播图片展示效果

<?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="com.example.a2_.MainActivity" 

<android.support.v4.view.ViewPager
  android:id="@+id/vp"
  android:layout_width="match_parent"
  android:layout_height="250dp" 
</android.support.v4.view.ViewPager 

<LinearLayout
  android:orientation="vertical"
  android:gravity="center"
  android:background="#66000000"
  android:layout_alignBottom="@id/vp"
  android:layout_width="match_parent"
  android:layout_height="50dp" 

  <TextView
    android:id="@+id/desc"
    android:text="描述文本"
    android:textColor="#ffffff"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" / 

  <LinearLayout
    android:id="@+id/layout_dot"
    android:orientation="horizontal"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" 

  </LinearLayout 
</LinearLayout 
</RelativeLayout 

package com.example.a2_;
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.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
private static final int UPDATE_ITEM = 1;
private ArrayList<ImageView  imageViews = new ArrayList< ();
private int[] imageResIds = {R.mipmap.icon_1, R.mipmap.icon_2, R.mipmap.icon_3,
R.mipmap.icon_4, R.mipmap.icon_5};
private String[] descs = {"为梦想坚持", "我相信我是黑马", "黑马公开课", "Google/IO", "轻松1w+"};
private ViewPager viewPager;
private TextView tv_desc;
private LinearLayout layout_dot;
private int count = 10000000;
private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case UPDATE_ITEM:
upDataItem();
break;
}
super.handleMessage(msg);
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//初始化控件
viewPager = (ViewPager) findViewById(R.id.vp);
tv_desc = (TextView) findViewById(R.id.desc);
layout_dot = (LinearLayout) findViewById(R.id.layout_dot);
//给viewPager设置适配器
viewPager.setAdapter(new MyPagerAdapter());
//对viewPager设置监听器
viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
//当页面滚动时触发的时间
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
//当页面被选中时触发的方法
@Override
public void onPageSelected(int position) {
//对position进行处理
position = position % imageViews.size();
//当页面被选中的时候,改变描述文本
tv_desc.setText(descs[position]);
changeDots(position);
}
//当页面状态滚动状态发生改变时触发的事件
@Override
public void onPageScrollStateChanged(int state) {
//当页面空闲状态被改变的时候
if (state == viewPager.SCROLL_STATE_IDLE) {
handler.sendEmptyMessageDelayed(UPDATE_ITEM, 3000);
} else {
handler.removeMessages(UPDATE_ITEM);
}
}
});
//初始化图片
initImage();
//初始化文字下方的点
initDot();
//当加载页面的时候,默认让第一个文本加载出来
//    initDescFirst();
//使两边都可以无限轮播
viewPager.setCurrentItem(count / 2);
//页面加载时更新
upDataItem();
}
private void upDataItem() {
int index = viewPager.getCurrentItem();
viewPager.setCurrentItem(++index);
handler.sendEmptyMessageDelayed(UPDATE_ITEM, 3000);
}
//选中对应的原点
private void changeDots(int position) {
//先把所有的点恢复为白色
for (int i = 0; i < layout_dot.getChildCount(); i++) {
View view = layout_dot.getChildAt(i);
view.setSelected(false);
}
//获取当前被选中的条目 设置为选中状态
layout_dot.getChildAt(position).setSelected(true);
}
//初始化文字下方的点
private void initDot() {
LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(10, 10);
layoutParams.setMargins(4, 4, 4, 4);
for (int i = 0; i < imageViews.size(); i++) {
View view = new View(this);
view.setBackgroundResource(R.drawable.seletor_dot);
view.setLayoutParams(layoutParams);
layout_dot.addView(view);
}
}
//当加载页面的时候,默认让第一个文本加载出来
private void initDescFirst() {
tv_desc.setText(descs[0]);
changeDots(0);
}
//添加图片,准备一个ImageView集合,用来交给instantiateItem添加到页面
private void initImage() {
for (int i = 0; i < imageResIds.length; i++) {
//创建出ImageView对象
ImageView imageView = new ImageView(getApplicationContext());
imageView.setImageResource(imageResIds[i]);
imageViews.add(imageView);
}
}
private class MyPagerAdapter extends PagerAdapter {
@Override
public int getCount() {
return count;
}
@Override
public boolean isViewFromObject(View view, Object object) {
//判断这个view是不是通过instantiateItem创建出来的
return view == object;
}
//用来创建条目
@Override
public Object instantiateItem(ViewGroup container, int position) {
position = position % imageResIds.length;
//获取条目
ImageView imageView = imageViews.get(position);
container.addView(imageView);
return imageView;
}
//用来销毁条目,,且最多会创建出三个条目,多出来的条目将会被销毁
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
//销毁创建的条目
container.removeView((View) object);
}
}
@Override
protected void onStart() {
super.onStart();
//当页面显示的时候,更新轮播图
handler.sendEmptyMessageDelayed(UPDATE_ITEM, 3000);
}
@Override
protected void onStop() {
super.onStop();
//当页面不可见时,停止更新
handler.removeCallbacksAndMessages(null);
}
}