本文是基于viewpager实现的无限自动轮播banner，供大家参考，具体内容如下
分为四步去实现：
第一步是有限手动轮播；
第二步是无限轮播；
第三步是自动轮播；
第四步是指示器适配
第一步：有限手动轮播实现
布局：
adapter实现：
public class banneradapter extends pageradapter {
private list bannerlist;
public banneradapter(list bannerlist) {
this.bannerlist = bannerlist;
}
@override
public int getcount() {
return bannerlist.size();
}
@override
public boolean isviewfromobject(@nonnull view view, @nonnull object object) {
return view == object;
}
@nonnull
@override
public object instantiateitem(@nonnull viewgroup container, int position) {
imageview bannerimageview = new imageview(container.getcontext());
viewgroup.layoutparams lp = new viewgroup.layoutparams(viewgroup.layoutparams.match_parent, viewgroup.layoutparams.match_parent);
bannerimageview.setlayoutparams(lp);
bannerimageview.setscaletype(imageview.scaletype.fit_xy);
glide.with(container.getcontext()).load(bannerlist.get(position)).into(bannerimageview);
container.addview(bannerimageview);
return bannerimageview;
}
@override
public void destroyitem(@nonnull viewgroup container, int position, @nonnull object object) {
container.removeview((view) object);
}
}
activity中：
// scrollview中viewpager一定要设置高度，此处根据图片的宽高比来设定高度 int bannerwidth = (utils.getscreenwidth(getcontext()) - utils.dip2pixel(getcontext(), 24)); linearlayout.layoutparams lp = (linearlayout.layoutparams) bannerview.getlayoutparams(); lp.width = linearlayout.layoutparams.match_parent; lp.height = (int) (bannerwidth * 90f / 345); bannerview.setlayoutparams(lp); bannerview.setadapter(new banneradapter(geturllist()));
注意：scrollview包裹viewpager时，viewpager的高度一定要有确定值，否则内容无法加载出来，可以在xml中指定，也可以代码设定，但一定要有确定值。
第二步：无限轮播
无限轮播只需要在有限轮播的基础上，做以下两个改动点，修改getcount返回值且在加载数据时获取正确的数据源即可
public class banneradapter extends pageradapter {
private list bannerlist;
public banneradapter(list bannerlist) {
this.bannerlist = bannerlist;
}
@override
public int getcount() {
// return bannerlist.size(); // before
return integer.max_value; // now
}
@override
public boolean isviewfromobject(@nonnull view view, @nonnull object object) {
return view == object;
}
@nonnull
@override
public object instantiateitem(@nonnull viewgroup container, int position) {
imageview bannerimageview = new imageview(container.getcontext());
int realposition = position % bannerlist.size(); // 获取要加载数据的真实位置
viewgroup.layoutparams lp = new viewgroup.layoutparams(viewgroup.layoutparams.match_parent, viewgroup.layoutparams.match_parent);
bannerimageview.setlayoutparams(lp);
bannerimageview.setscaletype(imageview.scaletype.fit_xy);
// glide.with(container.getcontext()).load(bannerlist.get(position)).into(bannerimageview); // before
glide.with(container.getcontext()).load(bannerlist.get(realposition)).into(bannerimageview); // now
container.addview(bannerimageview);
return bannerimageview;
}
@override
public void destroyitem(@nonnull viewgroup container, int position, @nonnull object object) {
container.removeview((view) object);
}
}
修改完发现banner只能向右无限轮播，第一次左滑滑不动，这个时候我们强制设置viewpager位置在中间就可以解决这个问题了
bannerview.setadapter(new banneradapter(geturllist())); bannerview.setcurrentitem(geturllist().size() * 5);
第三步：自动轮播
handler每隔轮播间隔发送消息，设置viewpager为下一个位置
private runnable bannerrunnable = new runnable() {
@override
public void run() {
bannerview.setcurrentitem(bannerview.getcurrentitem() 1);
mhandler.postdelayed(bannerrunnable, 3000);
}
};
bannerview.addonpagechangelistener(new viewpager.onpagechangelistener() {
@override
public void onpagescrolled(int position, float positionoffset, int positionoffsetpixels) {
}
@override
public void onpageselected(int position) {
// 手滑动到某一位置，重新开始计时
start();
}
@override
public void onpagescrollstatechanged(int state) {
}
});
private void start() {
mhandler.removecallbacksandmessages(null);
mhandler.postdelayed(bannerrunnable, 3000);
}
第四步：添加指示器
指示器样式及表现可以自己去根据需求实现，以相对简单和常见的小圆圈指示器为例，添加和banner数量相同的小圆圈，小圆圈设置selector，在选中时为黑色选中样式，在非选中时为灰色默认样式，根据当前选中的banner的实际position，设置指示器的selected属性，从而展示不同的样式
private void initindicator() {
for (int i = 0; i < geturllist().size(); i ) {
view view = new view(getactivity());
linearlayout.layoutparams lp = new linearlayout.layoutparams(utils.dip2pixel(getactivity(), 6), utils.dip2pixel(getactivity(), 6));
lp.rightmargin = utils.dip2pixel(getactivity(), 8);
view.setlayoutparams(lp);
view.setbackgroundresource(r.drawable.selector_indicator_view);
view.setselected(i == 0);
llindicatorview.addview(view);
}
}
private void initbannerview() {
bannerview.addonpagechangelistener(new viewpager.onpagechangelistener() {
@override
public void onpagescrolled(int position, float positionoffset, int positionoffsetpixels) {
}
@override
public void onpageselected(int position) {
// 手滑动到某一位置，重新开始计时
realposition = 0;
realposition = position % geturllist().size();
// 根据当前滑动到的banner设置指示器的状态
for (int i = 0; i < llindicatorview.getchildcount(); i ) {
llindicatorview.getchildat(i).setselected(i == realposition);
}
start();
}
@override
public void onpagescrollstatechanged(int state) {
}
});
}
附：utils文件
public class utils {
public static void setfullscreen(activity activity) {
if (build.version.sdk_int >= build.version_codes.m) {
viewgroup decorview = (viewgroup) activity.getwindow().getdecorview();
decorview.setsystemuivisibility(view.system_ui_flag_layout_fullscreen | view.system_ui_flag_light_status_bar);
activity.getwindow().setstatusbarcolor(color.transparent);
}
}
public static int dip2pixel(context context, float n) {
int value = (int) typedvalue.applydimension(typedvalue.complex_unit_dip, n, context.getresources().getdisplaymetrics());
return value;
}
/**
* 获取屏幕宽度
* @param context
* @return 屏幕宽度
*/
public static int getscreenwidth(context context) {
windowmanager wm = (windowmanager) context
.getsystemservice(context.window_service);
displaymetrics outmetrics = new displaymetrics();
wm.getdefaultdisplay().getmetrics(outmetrics);
return outmetrics.widthpixels;
}
}
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。
