版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/wode_dream/article/details/51130759
最近，在看慕课网上的android课程，想学习其它达人的技巧与编程方法。ViewPager箭头指示器的效果如下：
咱们主要看代码，共分三步，步骤如下：
第一步：编写ViewPagerIndicator类，代码如下：
public class ViewPagerIndicator extends LinearLayout
{
public static final int DEFAULT_VISIBLE_TABS=4;
private Paint paint;
private Path path;
private int mTriangleWidth;
private int mTriangleHeight;
private static final float RADIO_TRIANGEL_WIDTH=1/6f;
private int mInitTranslationX;
private int mTranslationX=0;
private int visibleTabs=DEFAULT_VISIBLE_TABS;
/**
* 防止用户覆盖ViewPagerIndicator中的ViewPager.OnPageChangeListener，所以在这里设置一个回调接口。
*/
private ViewPagerListener viewPagerListener;
public interface ViewPagerListener
{
void onPageScrolled(int position, float positionOffset, int positionOffsetPixels);
void onPageSelected(int position);
void onPageScrollStateChanged(int state);
}
public ViewPagerIndicator(Context context)
{
this(context,null);
}
public ViewPagerIndicator(Context context, AttributeSet attrs)
{
super(context, attrs);
//初始化画笔
paint=new Paint();
paint.setAntiAlias(true);
paint.setColor(Color.parseColor("#ffffff"));
paint.setStyle(Paint.Style.FILL);
paint.setPathEffect(new CornerPathEffect(3));
}
/**
* 设置显示的tab个数
* @param count
*/
public void setVisibleTabs(int count)
{
if(count<=0)
{
visibleTabs=ViewPagerIndicator.DEFAULT_VISIBLE_TABS;
}else{
this.visibleTabs=count;
}
}
/**
* 动态添加tab
* @param titles
*/
public void addTabs(List<String> titles)
{
for(String title:titles)
{
TextView tv=new TextView(getContext());
int tabWidth=getScreenWith()/visibleTabs;
LinearLayout.LayoutParams lp=new LinearLayout.LayoutParams(tabWidth, ViewGroup.LayoutParams.MATCH_PARENT);
tv.setLayoutParams(lp);
tv.setTextColor(Color.parseColor("#ffffffff"));
tv.setTextSize(TypedValue.COMPLEX_UNIT_SP,15);
tv.setText(title);
tv.setGravity(Gravity.CENTER);
addView(tv);
}
}
/**
* 设置三角形的初始位置和宽高
* @param w
* @param h
* @param oldw
* @param oldh
*/
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh)
{
super.onSizeChanged(w, h, oldw, oldh);
mTriangleWidth=(int)(w/visibleTabs*RADIO_TRIANGEL_WIDTH);
mTriangleHeight=mTriangleWidth/2;
mInitTranslationX=w/visibleTabs/2-mTriangleWidth/2;
initTriangle();
}
/**
* 绘制三角形
*/
private void initTriangle()
{
path=new Path();
path.moveTo(0,0);
path.lineTo(mTriangleWidth,0);
path.lineTo(mTriangleWidth/2,-mTriangleHeight);
path.close();
}
/**
* 更新三角形的位置
* @param canvas
*/
@Override
protected void dispatchDraw(Canvas canvas)
{
canvas.save();
canvas.translate(mInitTranslationX+mTranslationX,getHeight());
canvas.drawPath(path,paint);
canvas.restore();
super.dispatchDraw(canvas);
}
/**
* 设置tab滑动到未显示的区域
* @param position
* @param offset
*/
public void scrollTo(int position,float offset)
{
int tabWidth=getScreenWith()/visibleTabs;
mTranslationX=(int)(tabWidth*(offset+position));
if((position+2)>=visibleTabs&&offset>0&&visibleTabs<getChildCount())
{
if(visibleTabs!=1)
{
this.scrollTo((int)(tabWidth*(offset+position+2-visibleTabs)),0);
}else{
this.scrollTo(mTranslationX,0);
}
}
invalidate();
}
/**
* 设置ViewPager
* @param viewPager
*/
public void setViewPager(ViewPager viewPager)
{
viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels)
{
scrollTo(position,positionOffset);
if(viewPagerListener!=null)
{
viewPagerListener.onPageScrolled(position,positionOffset,positionOffsetPixels);
}
}
@Override
public void onPageSelected(int position) {
if(viewPagerListener!=null)
{
viewPagerListener.onPageSelected(position);
}
}
@Override
public void onPageScrollStateChanged(int state) {
if(viewPagerListener!=null)
{
viewPagerListener.onPageScrollStateChanged(state);
}
}
});
}
public void setViewPagerListener(ViewPagerListener viewPagerListener)
{
this.viewPagerListener=viewPagerListener;
}
@Override
protected void onFinishInflate() {
super.onFinishInflate();
}
private int getScreenWith()
{
WindowManager windowManager=(WindowManager)getContext().getSystemService(Context.WINDOW_SERVICE);
Point point=new Point();
windowManager.getDefaultDisplay().getSize(point);
return point.x;
}
}<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.zfeng.viewpagerindicator.MainActivity"
android:background="@android:color/white">
<com.zfeng.widget.ViewPagerIndicator
android:id="@+id/indicator"
android:layout_width="match_parent"
android:layout_height="40dip"
android:background="@android:color/holo_blue_light"/>
<android.support.v4.view.ViewPager
android:id="@+id/viewpager"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</LinearLayout>第三步，在MainActivity中引用，代码如下：
public class MainActivity extends AppCompatActivity
{
private ViewPagerIndicator indicator;
private ViewPager viewPager;
private List<String> mTitles= Arrays.asList("tab1","tab2","tab3","tab4","tab5","tab6","tab7","tab8","tab9");
private List<FragmentSimple> mFragments=new ArrayList<>();
private FragmentPagerAdapter fragmentPagerAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.activity_main);
initView();
initDatas();
indicator.setVisibleTabs(4);
indicator.addTabs(mTitles);
viewPager.setAdapter(fragmentPagerAdapter);
indicator.setViewPager(viewPager);
indicator.setViewPagerListener(new ViewPagerIndicator.ViewPagerListener() {
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
@Override
public void onPageSelected(int position) {
}
@Override
public void onPageScrollStateChanged(int state) {
}
});
}
private void initView()
{
indicator=(ViewPagerIndicator)findViewById(R.id.indicator);
viewPager=(ViewPager)findViewById(R.id.viewpager);
}
private void initDatas()
{
for(String str:mTitles)
{
FragmentSimple fragmentSimple=FragmentSimple.newInstance(str);
mFragments.add(fragmentSimple);
}
fragmentPagerAdapter=new FragmentPagerAdapter(getSupportFragmentManager()) {
@Override
public Fragment getItem(int position) {
return mFragments.get(position);
}
@Override
public int getCount() {
return mFragments.size();
}
};
}
}
public class FragmentSimple extends Fragment
{
private String title;
public static final String ARGS="FragmentSimpleArgs";
public static FragmentSimple newInstance(String title)
{
Bundle bundle=new Bundle();
bundle.putString(FragmentSimple.ARGS,title);
FragmentSimple fragmentSimple=new FragmentSimple();
fragmentSimple.setArguments(bundle);
return fragmentSimple;
}
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState)
{
Bundle bundle=getArguments();
if(bundle!=null)
{
title=bundle.getString(FragmentSimple.ARGS);
}else{
title="title";
}
TextView tv=new TextView(getContext());
tv.setText(title);
tv.setTextColor(Color.parseColor("#000000"));
tv.setGravity(Gravity.CENTER);
return tv;
}
}