这一篇，来写源码解析，其实并不算困难
主要就是PagerSlidingTabStrip这个自定义控件，PagerSlidingTabStrip继承自HorizontalScrollView。首先在成员变量里定义了一些绘图需要的属性，也设置了默认值，比如下面这些：
private final PageListener pageListener = new PageListener();
// @formatter:on
public OnPageChangeListener delegatePageListener;
private LinearLayout.LayoutParams defaultTabLayoutParams;
private LinearLayout.LayoutParams expandedTabLayoutParams;
/**
* HorizontalScrollView里的容器
*/
private LinearLayout tabsContainer;
private ViewPager pager;
private int tabCount;
private int currentPosition = 0;
private float currentPositionOffset = 0f;
private Paint rectPaint;
private Paint dividerPaint;
private int indicatorColor = 0xFF666666;
private int underlineColor = 0x1A000000;
private int dividerColor = 0x1A000000;
private boolean shouldExpand = false;
private boolean textAllCaps = true;
/**
* 滑动Tab时之前的Tab移动的距离
*/
private int scrollOffset = 52;
private int indicatorHeight = 8;
private int underlineHeight = 2;
//竖直分割线的内边矩
private int dividerPadding = 12;
private int tabPadding = 24;
private int dividerWidth = 1;
private int tabTextSize = 12;
private int tabTextColor = 0xFF666666;
private Typeface tabTypeface = null;
private int tabTypefaceStyle = Typeface.BOLD;
private int lastScrollX = 0;
private int tabBackgroundResId = R.drawable.background_tab;
然后是构造方法，这里面获取了自定义属性的值，以及初始化了相关画笔，代码如下：
public PagerSlidingTabStrip(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
setFillViewport(true);
setWillNotDraw(false);
tabsContainer = new LinearLayout(context);
tabsContainer.setOrientation(LinearLayout.HORIZONTAL);
tabsContainer.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
addView(tabsContainer);
DisplayMetrics dm = getResources().getDisplayMetrics();
scrollOffset = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, scrollOffset, dm);
indicatorHeight = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, indicatorHeight, dm);
underlineHeight = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, underlineHeight, dm);
dividerPadding = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dividerPadding, dm);
tabPadding = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, tabPadding, dm);
dividerWidth = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dividerWidth, dm);
tabTextSize = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, tabTextSize, dm);
// get system attrs (android:textSize and android:textColor)
TypedArray a = context.obtainStyledAttributes(attrs, ATTRS);
tabTextSize = a.getDimensionPixelSize(0, tabTextSize);
tabTextColor = a.getColor(1, tabTextColor);
a.recycle();
// get custom attrs
a = context.obtainStyledAttributes(attrs, R.styleable.PagerSlidingTabStrip);
indicatorColor = a.getColor(R.styleable.PagerSlidingTabStrip_pstsIndicatorColor, indicatorColor);
Log.d("alan","indicatorColor---------~~~~"+indicatorColor);
underlineColor = a.getColor(R.styleable.PagerSlidingTabStrip_pstsUnderlineColor, underlineColor);
dividerColor = a.getColor(R.styleable.PagerSlidingTabStrip_pstsDividerColor, dividerColor);
indicatorHeight = a.getDimensionPixelSize(R.styleable.PagerSlidingTabStrip_pstsIndicatorHeight, indicatorHeight);
underlineHeight = a.getDimensionPixelSize(R.styleable.PagerSlidingTabStrip_pstsUnderlineHeight, underlineHeight);
dividerPadding = a.getDimensionPixelSize(R.styleable.PagerSlidingTabStrip_pstsDividerPadding, dividerPadding);
tabPadding = a.getDimensionPixelSize(R.styleable.PagerSlidingTabStrip_pstsTabPaddingLeftRight, tabPadding);
tabBackgroundResId = a.getResourceId(R.styleable.PagerSlidingTabStrip_pstsTabBackground, tabBackgroundResId);
shouldExpand = a.getBoolean(R.styleable.PagerSlidingTabStrip_pstsShouldExpand, shouldExpand);
scrollOffset = a.getDimensionPixelSize(R.styleable.PagerSlidingTabStrip_pstsScrollOffset, scrollOffset);
textAllCaps = a.getBoolean(R.styleable.PagerSlidingTabStrip_pstsTextAllCaps, textAllCaps);
a.recycle();
rectPaint = new Paint();
rectPaint.setAntiAlias(true);
rectPaint.setStyle(Style.FILL);
dividerPaint = new Paint();
dividerPaint.setAntiAlias(true);
dividerPaint.setStrokeWidth(dividerWidth);
//当Tab个数不超过屏幕宽度时
defaultTabLayoutParams = new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.MATCH_PARENT);
//当Tab个数超过屏幕宽度时
expandedTabLayoutParams = new LinearLayout.LayoutParams(0, LayoutParams.MATCH_PARENT, 1.0f);
if (locale == null) {
locale = getResources().getConfiguration().locale;
}
}
解释：HorizontalScrollView里面只有一个子控件，就是tabsContainer，一个线性布局，这个用来装多个TextView用来做为Tab标签，tabsContainer有两种设定宽高的方式，一个是当Tab很少，不足以超过屏幕时是这个
//当Tab个数不超过屏幕宽度时
defaultTabLayoutParams = new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.MATCH_PARENT);
当Tab很多，超过屏幕宽度了时，就是按权重了
//当Tab个数超过屏幕宽度时
expandedTabLayoutParams = new LinearLayout.LayoutParams(0, LayoutParams.MATCH_PARENT, 1.0f);
当外部调用setViewPager时，会走notifyDataSetChanged()方法，这是notifyDataSetChanged方法
public void notifyDataSetChanged() {
tabsContainer.removeAllViews();
tabCount = pager.getAdapter().getCount();
for (int i = 0; i < tabCount; i++) {
//Tab是图标类
if (pager.getAdapter() instanceof IconTabProvider) {
addIconTab(i, ((IconTabProvider) pager.getAdapter()).getPageIconResId(i));
} else {//如果Tab是文字类
addTextTab(i, pager.getAdapter().getPageTitle(i).toString());
}
}
updateTabStyles();
getViewTreeObserver().addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
@SuppressWarnings("deprecation")
@SuppressLint("NewApi")
@Override
public void onGlobalLayout() {
if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN) {
getViewTreeObserver().removeGlobalOnLayoutListener(this);
} else {
getViewTreeObserver().removeOnGlobalLayoutListener(this);
}
currentPosition = pager.getCurrentItem();
scrollToChild(currentPosition, 0);
}
});
}
即在线性布局里循环添加TextView,通过addTextTab和addTab方法进行添加，具体如下：
/**
* 添加每一个文字Tab
*/
private void addTextTab(final int position, String title) {
TextView tab = new TextView(getContext());
tab.setText(title);
tab.setGravity(Gravity.CENTER);
tab.setSingleLine();
addTab(position, tab);
}
private void addTab(final int position, View tab) {
tab.setFocusable(true);
tab.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
pager.setCurrentItem(position);
}
});
tab.setPadding(tabPadding, 0, tabPadding, 0);
tabsContainer.addView(tab, position, shouldExpand ? expandedTabLayoutParams : defaultTabLayoutParams);
}
add完毕后又通过updateTabStyles这个方法来给TextView设置背景和文字属性等：
private void updateTabStyles() {
for (int i = 0; i < tabCount; i++) {
View v = tabsContainer.getChildAt(i);
v.setBackgroundResource(tabBackgroundResId);
if (v instanceof TextView) {
TextView tab = (TextView) v;
tab.setTextSize(TypedValue.COMPLEX_UNIT_PX, tabTextSize);
tab.setTypeface(tabTypeface, tabTypefaceStyle);
tab.setTextColor(tabTextColor);
// setAllCaps() is only available from API 14, so the upper case is made manually if we are on a
// pre-ICS-build
if (textAllCaps) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
tab.setAllCaps(true);
} else {
tab.setText(tab.getText().toString().toUpperCase(locale));
}
}
}
}
}
还要根据ViewPager的位置滑动Tab到指定位置，是这么做的：
private void scrollToChild(int position, int offset) {
if (tabCount == 0) {
return;
}
int newScrollX = tabsContainer.getChildAt(position).getLeft() + offset;
if (position > 0 || offset > 0) {
newScrollX -= scrollOffset;
}
if (newScrollX != lastScrollX) {
lastScrollX = newScrollX;
scrollTo(newScrollX, 0);
}
}
在onDraw方法里面，绘制Tab底部指针和底线：
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
if (isInEditMode() || tabCount == 0) {
return;
}
final int height = getHeight();
// draw indicator line
rectPaint.setColor(indicatorColor);
// Log.d("alan","indicatorColor---->"+indicatorColor);
// default: line below current tab
View currentTab = tabsContainer.getChildAt(currentPosition);
float lineLeft = currentTab.getLeft();
float lineRight = currentTab.getRight();
// if there is an offset, start interpolating left and right coordinates between current and next tab
if (currentPositionOffset > 0f && currentPosition < tabCount - 1) {
View nextTab = tabsContainer.getChildAt(currentPosition + 1);
final float nextTabLeft = nextTab.getLeft();
final float nextTabRight = nextTab.getRight();
lineLeft = (currentPositionOffset * nextTabLeft + (1f - currentPositionOffset) * lineLeft);
lineRight = (currentPositionOffset * nextTabRight + (1f - currentPositionOffset) * lineRight);
}
//画Tab下面的指针
canvas.drawRect(lineLeft, height - indicatorHeight, lineRight, height, rectPaint);
// draw underline
rectPaint.setColor(underlineColor);
canvas.drawRect(0, height - underlineHeight, tabsContainer.getWidth(), height, rectPaint);
// draw divider
dividerPaint.setColor(dividerColor);
for (int i = 0; i < tabCount - 1; i++) {
View tab = tabsContainer.getChildAt(i);
canvas.drawLine(tab.getRight(), dividerPadding, tab.getRight(), height - dividerPadding, dividerPaint);
}
}
到现在，就分析完了，认为主要难度在于滑动的距离计算，还有一些坐标计算，通过这个源码分析，还是能学到很多自定义控件知识的
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