ViewPager 的 PagerIndicator

public class PagerIndicator extends LinearLayout implements OnPageChangeListener, OnClickListener {private List<String> mTitles;private int mTabCount;private int mTitleItemWidth;private int mLineColor;private int mSelectedTextColor;private int mNorTextColor;private int mTextSize = 17;private int mLineWidth;private Paint mLinePaint;private float mTranslationX;private ViewPager mViewPager;private List<TextView> mTextViewList;private OnViewPagerChangeListener listener;public interface OnViewPagerChangeListener{void onPageScrolled(int position, float positionOffset,int positionOffsetPixels);}public PagerIndicator(Context context, AttributeSet attrs) {super(context, attrs);init();}private void init() {mLineColor = getResources().getColor(R.color.indicator_bottom_line_color);mSelectedTextColor = getResources().getColor(R.color.indicator_selected_txt_color);mNorTextColor = getResources().getColor(R.color.indicator_un_selected_txt_color);mLineWidth = DensityConverter.dp2px(getContext(), 1);mLinePaint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.DITHER_FLAG);mLinePaint.setColor(mLineColor);mLinePaint.setStrokeWidth(mLineWidth);mLinePaint.setStrokeCap(Cap.ROUND);}@Overrideprotected void onSizeChanged(int w, int h, int oldw, int oldh) {if(mTitles != null && mTitles.size() > 0 ){mTitleItemWidth = w / mTitles.size();}}@SuppressWarnings("deprecation")public void setViewPager(ViewPager viewPager){mViewPager = viewPager;initTitles();initTitleItemView();mViewPager.setOnPageChangeListener(this);}private void initTitleItemView() {mTextViewList = new ArrayList<TextView>();if(getChildCount() > 0){  this.removeAllViews();}for(int i = 0 ; i < mTabCount; i++){TextView titleTv  = new TextView(getContext());LinearLayout.LayoutParams params = new LayoutParams(0, android.view.ViewGroup.LayoutParams.MATCH_PARENT);params.weight = 1;titleTv.setText(mTitles.get(i));titleTv.setId(i);titleTv.setGravity(Gravity.CENTER);  titleTv.setTextColor(i == 0 ? mSelectedTextColor : mNorTextColor);titleTv.setTextSize(TypedValue.COMPLEX_UNIT_SP, mTextSize);titleTv.setLayoutParams(params);titleTv.setOnClickListener(this);addView(titleTv);mTextViewList.add(titleTv);}}private void initTitles(){PagerAdapter adapter = mViewPager.getAdapter();mTabCount = adapter.getCount();mTitles = new ArrayList<String>();for(int i = 0 ; i < mTabCount ; i++){String title = (String) adapter.getPageTitle(i);mTitles.add(title);}}@Overridepublic void onPageScrollStateChanged(int position) {}@Overridepublic void onPageScrolled(int position, float positionOffset,int positionOffsetPixels) {if(null != listener){listener.onPageScrolled(position, positionOffset, positionOffsetPixels);}mTranslationX = getWidth() / mTabCount * (position + positionOffset);for(int i = 0 ; i < mTextViewList.size() ; i++){TextView textView = mTextViewList.get(i);if(position == i){textView.setTextColor(mSelectedTextColor);}else{textView.setTextColor(mNorTextColor);}}invalidate();}@Overridepublic void onPageSelected(int state) {}//绘制下划线@Overrideprotected void dispatchDraw(Canvas canvas) {super.dispatchDraw(canvas);canvas.save();canvas.translate(mTranslationX, getHeight() - mLineWidth / 2);canvas.drawLine(0, 0, mTitleItemWidth, 0, mLinePaint);canvas.restore();}@Overridepublic void onClick(View v) {int id = v.getId();mViewPager.setCurrentItem(id);}public void setOnViewPagerChangeListener(OnViewPagerChangeListener l) {this.listener = l;}}

核心代码:

计算需要移动的距离

mTranslationX = getWidth() / mTabCount * (position + positionOffset);for(int i = 0 ; i < mTextViewList.size() ; i++){TextView textView = mTextViewList.get(i);if(position == i){textView.setTextColor(mSelectedTextColor);}else{textView.setTextColor(mNorTextColor);}}invalidate();

绘制背景

@Overrideprotected void dispatchDraw(Canvas canvas) {super.dispatchDraw(canvas);canvas.save();canvas.translate(mTranslationX, getHeight() - mLineWidth / 2);canvas.drawLine(0, 0, mTitleItemWidth, 0, mLinePaint);canvas.restore();}