Android源码解析-仿今日头条PagerSlidingTabStrip滑动页面导航效果

最近项目中用到了滑动页面,也就是和目前市场上很火的"今日头条"页面滑动类似,在网上找了一下,大部分都是用ViewPager来实现的,刚开始我用的是ViewPager+ViewGroup,上面的标题按钮用的是HorizontalScrollView,写完之后感觉效果比较生硬,果断换掉,发现了一个效果比较好的第三方,也就是今天的主题:PagerSlidingTabStrip.好了,下面来具体介绍一下PagerSlidingTabStrip,进行一下源码解析. ### 一:到GitHub上去下载源码和Demo GitHub地址: https://github.com/astuetz/PagerSlidingTabStrip 先看一下demo的样子吧 ![](https://docs.gechiui.com/gc-content/uploads/sites/kancloud/2016-04-18_57144ed5d0186.jpg) ![](https://docs.gechiui.com/gc-content/uploads/sites/kancloud/2016-04-18_57144ed600b7e.jpg) ### 二:把PagerSlidingTabStrip导入我们的项目中然后在我们的布局文件中进行声明: ~~~ <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res/com.hankkin.PagerSlidingTabStrip" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <com.hankkin.PagerSlidingTabStrip.view.PagerSlidingTabStrip android:id="@+id/tab" app:pstsShouldExpand="false" app:pstsUnderlineHeight="2dp" app:pstsIndicatorHeight="2dp" app:pstsIndicatorColor="@android:color/holo_blue_light" app:selectedTabTextColor="@android:color/holo_blue_light" app:pstsDividerColor="@android:color/transparent" app:pstsTabBackground="@drawable/background" android:background="@android:color/white" android:layout_width="match_parent" android:layout_height="55dp"/> <android.support.v4.view.ViewPager android:id="@+id/pager" android:layout_width="match_parent" android:layout_height="match_parent"/> </LinearLayout> ~~~ 上面的也就是我们的标题滑动按钮,下面的ViewPager用来存放我们的内容 ### 三:创建Adapter ~~~ package com.hankkin.PagerSlidingTabStrip.adapter; import android.support.v4.app.Fragment; import android.support.v4.app.FragmentManager; import android.support.v4.app.FragmentPagerAdapter; import com.hankkin.PagerSlidingTabStrip.fragment.AndroidFragment; import com.hankkin.PagerSlidingTabStrip.fragment.JavaFragment; import com.hankkin.PagerSlidingTabStrip.fragment.ObjectCFragment; import java.util.List; /** * Created by Hankkin on 15/9/20. */ public class MyAdapter extends FragmentPagerAdapter { private AndroidFragment androidFragment; private JavaFragment javaFragment; private ObjectCFragment objectCFragment; private String[] titles; public MyAdapter(FragmentManager fm,String[] titles) { super(fm); this.titles = titles; } @Override public Fragment getItem(int position) { switch (position) { case 0: if (androidFragment == null) { androidFragment = new AndroidFragment(); } return androidFragment; case 1: if (javaFragment == null) { javaFragment = new JavaFragment(); } return javaFragment; case 2: if (objectCFragment == null) { objectCFragment = new ObjectCFragment(); } return objectCFragment; default: return null; } } @Override public int getCount() { return titles.length; } public String getPageTitle(int i){ return titles[i]; } } ~~~ 我这里用的是碎片Fragment,最下面的getPageTitle()是我们的PagerSlidingTabStrip中的方法,用来获取标题接下来我们初始化PagerSlidingTabStrip和ViewPager还有我们的碎片 ~~~ private void initViews(){ fragments = new ArrayList<>(); pagerTab = (PagerSlidingTabStrip) findViewById(R.id.tab); pager = (ViewPager) findViewById(R.id.pager); for (int i=0;i<titles.length;i++){ Fragment fragment = new Fragment(); fragments.add(fragment); } adapter = new MyAdapter(getSupportFragmentManager(),titles); pager.setAdapter(adapter); pagerTab.setViewPager(pager); } ~~~ 在Adapter中利用碎片管理器获取我们的碎片和标题相对应上.这里面需要注意提一下,如果碎片的个数比较少我们可以手动创建碎片,如果像今日头条很多的话也没关系,动态创建Fragment,因为我们可以看到头条的每个碎片中的内容都是类似的,所以说动态创建也未尝不可,只有个别特殊的我们也可以特殊处理. 就这么简单就可以实现类似头条的页面滑动效果,下面我们来看一下PagerSlidingTabStrip的源码吧,看懂了之后也方便我们进行改进. ### 四:PagerSlidingTabStrip源码解析首先我们看几个比较重要的属性 ~~~ private int indicatorColor = 0xFF666666;// 滑动指示器颜色 private int underlineColor = 0x1A000000;//在视图的底部的全宽度的线pstsunderlinecolor颜色 private int dividerColor = 0x1A000000;//选项卡之间的分隔pstsdividercolor颜色 private boolean shouldExpand = false;//pstsshouldexpand如果设置为TRUE，每个标签都给予同样的重量，默认为false private boolean textAllCaps = true;//pststextallcaps如果为真，所有选项卡标题都是大写，默认为true private int scrollOffset = 52;//pstsscrolloffset卷轴被选择的标签的偏移 private int indicatorHeight = 8;//滑动指示器pstsindicatorheight private int underlineHeight = 2;//在视图的底部的全宽度的线pstsunderlineheight高度 private int dividerPadding = 12;//pstsdividerpadding顶部和底部填充的分频器 private int tabPadding = 24;//pststabpaddingleftright左、右填充每个选项卡 private int dividerWidth = 1;//选项卡分割线宽度 private int tabTextSize = 12;//选项卡字体大小 private int tabTextColor = 0xFF666666;//选项卡字体颜色 private int selectedTabTextColor = 0xFF666666;//当前选中字体颜色 private Typeface tabTypeface = null; private int tabTypefaceStyle = Typeface.NORMAL; private int lastScrollX = 0; private int tabBackgroundResId = R.drawable.background;//pststabbackground背景绘制的每个标签，应该是一个statelistdrawable ~~~ 我们可以自己定义这些属性的值,因为可能默认的不太好看 1.首先看一下我们的构造会初始化一些什么属性 ~~~ public PagerSlidingTabStrip(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); setFillViewport(true);//默认使子view可以拉伸来填满整个屏幕 setWillNotDraw(false);//默认不执行OnDraw()方法 //初始化盛放按钮标题的线性布局 tabsContainer = new LinearLayout(context); tabsContainer.setOrientation(LinearLayout.HORIZONTAL); tabsContainer.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT)); addView(tabsContainer); DisplayMetrics dm = getResources().getDisplayMetrics(); //导入相应资源文件 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); //tab文字选中时的颜色,默认和滑动指示器的颜色一致 selectedTabTextColor=a.getColor(R.styleable.PagerSlidingTabStrip_selectedTabTextColor, indicatorColor); //初始化属性样式 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); defaultTabLayoutParams = new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.MATCH_PARENT); expandedTabLayoutParams = new LinearLayout.LayoutParams(0, LayoutParams.MATCH_PARENT, 1.0f); if (locale == null) { locale = getResources().getConfiguration().locale; } } ~~~ 这些基本都能看懂,主要都是初始化一些属性,代码中也有相应的注释,就不一一介绍了 2.定义ViewPager滑动监听器,设置当前pager的位置 ~~~ private class PageListener implements OnPageChangeListener { @Override public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { currentPosition = position; currentPositionOffset = positionOffset; scrollToChild(position, (int) (positionOffset * tabsContainer.getChildAt(position).getWidth())); invalidate(); if (delegatePageListener != null) { delegatePageListener.onPageScrolled(position, positionOffset, positionOffsetPixels); } } @Override public void onPageScrollStateChanged(int state) { if (state == ViewPager.SCROLL_STATE_IDLE) { scrollToChild(pager.getCurrentItem(), 0); } if (delegatePageListener != null) { delegatePageListener.onPageScrollStateChanged(state); } } @Override public void onPageSelected(int position) { selectedPosition = position; updateTabStyles(); if (delegatePageListener != null) { delegatePageListener.onPageSelected(position); } } } ~~~ 3.更新标题样式,也就是滑动到当前标题下设置标题状态 ~~~ 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)); } } if (i == selectedPosition) { tab.setTextColor(selectedTabTextColor); } } } } ~~~ 大体就差不多这些了,好了,给大家看一下我自己完善后的样子吧 ![](https://docs.gechiui.com/gc-content/uploads/sites/kancloud/2016-04-18_57144ed61cd13.jpg) 没有做太多调整,只是稍微的改了一下样式,里面还有一些比较细节的东西没有介绍,比如标题的宽度是平均分配还是分体字体长度进行设置,我们可以修改shouldExpand属性大家有兴趣的自己仔细研究一下吧.