关于ViewPager当前页卡指示器的简单实现方法

今天的案例为大家分享在Viewpager中当前页中指示器的实现方法，即通常放在ViewPager底部的实心小圆点，用于提示用户当前ViewPager所在的当前页是哪一页。整体实现的思想是通过给ViewPager设置OnPagerChangeListener在onPageSelected方法中设置当前页的选择状态

初始化的时候先初始化与list集合size相等的圆点个数：

int size = mList.size();
initPageIndicator(size);

然后是给ViewPager设置监听事件，并在onPageSelected方法中设置被选中的当前页圆点为选中状态：
mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

}

@Override
public void onPageSelected(int position) {

System.out.println(position+"-----------");
for (int i = 0; i < 4; i++) {
setIndicator(i, i == position);
}
}

@Override
public void onPageScrollStateChanged(int state) {

}
});

初始化指示点：

private void setIndicator(int i, boolean enabled) {
View view = mIndicator.getChildAt(i);
if (view != null) {
view.setEnabled(enabled);
}
}

private void initPageIndicator(int size) {
if (size <= 1) {
return;
}
for (int i = 0; i < size; i++) {
addPageIndicator(i);
}

setIndicator(0, true);
}

private void addPageIndicator(int i) {
View dot = new View(this);
dot.setBackgroundResource(R.drawable.dot_bg_black_selector);
LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(20, 20);
if (i != 0) {
params.leftMargin = 40;
}
params.topMargin = 20;
params.bottomMargin = 10;
dot.setEnabled(false);
dot.setLayoutParams(params);
mIndicator.addView(dot);
}

其中在初始化指示点的时候引用的drawable文件夹下的selector文件为：<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">

<item android:drawable="@android:drawable/alert_dark_frame" android:state_enabled="true"/>
<item android:drawable="@android:drawable/alert_light_frame" android:state_enabled="false"/>
</selector>
完整代码如下：

主布局文件：<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">

<android.support.v4.view.ViewPager
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/viewpager"
/>
<LinearLayout
android:id="@+id/indicator"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_gravity="center"
android:layout_marginBottom="10dp"
android:gravity="center"
android:orientation="horizontal"/>
</RelativeLayout>
ViewPager的Adapter代码：

/**
* Created by xiedong on 2017/4/7.
*/

public class ViewPagerAdapter extends PagerAdapter {

private List<View> mList = new ArrayList<>();
private LayoutInflater mInflater;

public ViewPagerAdapter(Context context , List<View> list) {
if (list == null || list.isEmpty()){
return;
}
mInflater = LayoutInflater.from(context);
mList = list;

// initView(list);

}

// private void initView(List<View> list) {
// for (View view :list){
// View item = mInflater.inflate(R.layout.viewpager_item,null);
// mList.add(item);
// }
// }

@Override
public int getCount() {
return null ==mList ? 0 :mList.size();
}

@Override
public boolean isViewFromObject(View view, Object object) {
return view==object;
}

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView(mList.get(position));
}

@Override
public Object instantiateItem(ViewGroup container, int position) {
container.addView(mList.get(position));
return mList.get(position);
}
}


功能代码：
/**
* Created by xiedong on 2017/4/7.
*/

public class IndicatorActivity extends Activity {

private ViewPager mViewPager;
private LinearLayout mIndicator;
private List<View> mList = new ArrayList<>();

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_indicator);

mViewPager = (ViewPager) findViewById(R.id.viewpager);
mIndicator = (LinearLayout) findViewById(R.id.indicator);

for (int i = 0; i < 4; i++) {
View item = LayoutInflater.from(this).inflate(R.layout.viewpager_item,null);
mList.add(item);
}

mViewPager.setAdapter(new ViewPagerAdapter(this,mList));

int size = mList.size();
initPageIndicator(size);
mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

}

@Override
public void onPageSelected(int position) {

System.out.println(position+"-----------");
for (int i = 0; i < 4; i++) {
setIndicator(i, i == position);
}
}

@Override
public void onPageScrollStateChanged(int state) {

}
});
}

private void setIndicator(int i, boolean enabled) { View view = mIndicator.getChildAt(i); if (view != null) { view.setEnabled(enabled); } } private void initPageIndicator(int size) { if (size <= 1) { return; } for (int i = 0; i < size; i++) { addPageIndicator(i); } setIndicator(0, true); } private void addPageIndicator(int i) { View dot = new View(this); dot.setBackgroundResource(R.drawable.dot_bg_black_selector); LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(20, 20); if (i != 0) { params.leftMargin = 40; } params.topMargin = 20; params.bottomMargin = 10; dot.setEnabled(false); dot.setLayoutParams(params); mIndicator.addView(dot); }
}


填充ViewPager的布局文件viewpager_item.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:background="@color/colorAccent"

android:layout_height="match_parent">

</LinearLayout>