Android仿今日头条滑动页面导航效果

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、看一下demo的样子吧

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:

<span style="font-size:14px;"><?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></span><span style="font-size:18px;">
</span>

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

<span style="font-size:14px;">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; 

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];
  } 

}
</span>

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

<span style="font-size:14px;"> 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);
  }</span>

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

<span style="font-size:14px;">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;
    }
  }</span>

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

<span style="font-size:14px;">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);
      }
    } 

  }</span>

3.更新标题样式,也就是滑动到当前标题下设置标题状态

<span style="font-size:14px;">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);
        }
      }
    } 

  }</span>

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

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.