简介

PagerSlidingTabStrip，是我个人经常使用到的一个和ViewPager配合的页面指示器，可以满足开发过程中常用的需求，如类似于今日头条的首页新闻内容导航栏等等，之前自己开发的JuheNews和正在开发的GankIOClient均有使用到它，所以想对其进行一个全面的介绍。



PagerSlidingTabStrip源码地址：

https://github.com/astuetz/PagerSlidingTabStrip

简单使用

• 添加库依赖

dependencies {
    compile ‘com.astuetz:pagerslidingtabstrip:1.0.1‘
}

• 定义布局文件

    <com.astuetz.PagerSlidingTabStrip
        android:id="@+id/psts_indicator"
        android:layout_width="match_parent"
        android:layout_height="40dp"/>

    <android.support.v4.view.ViewPager
        android:id="@+id/vp_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

• 关联ViewPager

public class MainActivity extends AppCompatActivity {

    @BindView(R.id.psts_indicator)
    PagerSlidingTabStrip pstsIndicator;
    @BindView(R.id.activity_main)
    LinearLayout activityMain;
    @BindView(R.id.vp_content)
    ViewPager vpContent;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ButterKnife.bind(this);
        MainPagerAdapter mainPagerAdapter = new MainPagerAdapter(getSupportFragmentManager());
        vpContent.setAdapter(mainPagerAdapter);
        pstsIndicator.setViewPager(vpContent);
    }
}

• 结果

• 后话
  看到这个效果，是不是很炸裂，如此的丑陋，上图是什么属性都没有修改默认的效果图，接着我们看下源码，看下可以从哪方面来进行改造。
  

  ---

源码解析

这个开源库，简单点说就是大家都非常熟悉的自定义View，所以，解读的方式可以从自定义属性到此视图的构造，onMeasure,onLayout, onDraw等等

1. 自定义的属性值

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="PagerSlidingTabStrip">
        <!--底部滑动指示器的颜色-->
        <attr name="pstsIndicatorColor" format="color" />
        <!--底部用于给指示器滑动的区域的颜色-->
        <attr name="pstsUnderlineColor" format="color" />
        <!--分割线的颜色-->
        <attr name="pstsDividerColor" format="color" />
        <!--指示器的高度-->
        <attr name="pstsIndicatorHeight" format="dimension" />
        <!--底部区域的高度-->
        <attr name="pstsUnderlineHeight" format="dimension" />
        <!--分割线与上下的间距-->
        <attr name="pstsDividerPadding" format="dimension" />
        <!--每个Tab的左右边距-->
        <attr name="pstsTabPaddingLeftRight" format="dimension" />
        <!--选中tab的滚动偏移量,个人基本没有用到过-->
        <attr name="pstsScrollOffset" format="dimension" />
        <!--每个Tab的背景图，StateListDrawable-->
        <attr name="pstsTabBackground" format="reference" />
        <!--是否根据tab均为位置，true的时候均分，默认为false,一般都是使用默认值-->
        <attr name="pstsShouldExpand" format="boolean" />
        <!--标题文本是否大写，默认为true-->
        <attr name="pstsTextAllCaps" format="boolean" />
    </declare-styleable>
</resources>

看下大致的布局和属性对号入座

2. PagerSlidingTabStrip.java类结构

类中的getter和setter方法，基本上和上面的自定义属性可以对上号，不仅可以在布局文件中定义，还可以通过java代码进行设置。

类中使用到的变量，大部分都是和自定义属性挂钩的，主要关注几个

• IconTabProvider
  类中比较关键的一些内容，接口IconTabProvider，ViewPager对应的Adapter实现该方法并返回每个ViewPager对应的图标即可实现图标指示器。

• PageListener <用户自定义的OnPagerListener的事件处理集成于此处>

    private class PageListener implements OnPageChangeListener {

        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            //存储当前位置信息
            currentPosition = position;
            currentPositionOffset = positionOffset;

            //滑动到子视图
            scrollToChild(position, (int) (positionOffset * tabsContainer.getChildAt(position).getWidth()));

            invalidate();//触发重绘

            //用户自定义的OnPagerChangeListener事件之onPagerScrolled
            if (delegatePageListener != null) {
                delegatePageListener.onPageScrolled(position, positionOffset, positionOffsetPixels);
            }
        }

        @Override
        public void onPageScrollStateChanged(int state) {
            //已经滑动完成，offset归0
            if (state == ViewPager.SCROLL_STATE_IDLE) {
                scrollToChild(pager.getCurrentItem(), 0);
            }

            //用户自定义的OnPagerChangeListener事件之onPageScrollStateChanged
            if (delegatePageListener != null) {
                delegatePageListener.onPageScrollStateChanged(state);
            }
        }

        @Override
        public void onPageSelected(int position) {
            //这里类内部没有做什么处理，只处理用户自定义的OnPagerSelected方法
            if (delegatePageListener != null) {
                delegatePageListener.onPageSelected(position);
            }
        }
    }

    /**
     *滑动指定子视图
     */
    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);
        }
    }

• PagerSlidingTabStrip构造方法
  构造方法的内容不多，基本上全是基本属性的获取，自定义View中常用的TypedArray ，记得回收recycle()，这里关注一下 TypedValue.applyDimension方法的使用，全部转换成px。

    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);
        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();

        /* 初始化矩形Paint */
        rectPaint = new Paint();
        rectPaint.setAntiAlias(true);
        rectPaint.setStyle(Style.FILL);
        /* 初始化分割线Paint */
        dividerPaint = new Paint();
        dividerPaint.setAntiAlias(true);
        dividerPaint.setStrokeWidth(dividerWidth);

        /* 是否延伸，默认WRAP_CONTENT,这种比较合理 */
        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;
        }
    }

• onDraw

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        if (isInEditMode() || tabCount == 0) {
            return;
        }

        final int height = getHeight();

        // 设置Indicator颜色
        rectPaint.setColor(indicatorColor);

        // 获取当前选中Tab
        View currentTab = tabsContainer.getChildAt(currentPosition);
        //获取Left,Right值
        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) {
            //结合下一个Tab获取当前要绘制的indicator的位置,这里的currentPositionOffset 比较关键，可以看到这个值是与ViewPager相关的，在onPagerScrolled方法中，这个值在不断的更新
            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);
        }
        // 绘制Indicator
        canvas.drawRect(lineLeft, height - indicatorHeight, lineRight, height, rectPaint);

        // 绘制UnderLine
        rectPaint.setColor(underlineColor);
        canvas.drawRect(0, height - underlineHeight, tabsContainer.getWidth(), height, rectPaint);

        // 绘制分割线
        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);
        }
    }

• setViewPager， setOnPageChangeListener
  一个用来与ViewPager联动，一个用来处理自定义的OnPagerListener逻辑

public void setViewPager(ViewPager pager) {
        this.pager = pager;

        if (pager.getAdapter() == null) {
            throw new IllegalStateException("ViewPager does not have adapter instance.");
        }

        pager.setOnPageChangeListener(pageListener);

        notifyDataSetChanged();
    }

    public void setOnPageChangeListener(OnPageChangeListener listener) {
        this.delegatePageListener = listener;
    }

3. PagerSlidingTabStrip综合用法

• 文本指示器选中后文本大小和颜色变化
  
  关键点在于实现自己的OnPagerListener

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ButterKnife.bind(this);
        MainPagerAdapter mainPagerAdapter = new MainPagerAdapter(getSupportFragmentManager());
        vpContent.setAdapter(mainPagerAdapter);
        pstsIndicator.setViewPager(vpContent);
        vpContent.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {
                updateTextStyle(position);
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });
        updateTextStyle(vpContent.getCurrentItem());
    }

    private void updateTextStyle(int position) {
        LinearLayout tabsContainer = (LinearLayout) pstsIndicator.getChildAt(0);
        for(int i=0; i< tabsContainer.getChildCount(); i++) {
            TextView textView = (TextView) tabsContainer.getChildAt(i);
            if(position == i) {
                textView.setTextSize(18);
                textView.setTextColor(getResources().getColor(R.color.colorToolbar));
            } else {
                textView.setTextSize(12);
                textView.setTextColor(getResources().getColor(R.color.colorBlack));
            }
        }
    }

• 图标指示器选中图标颜色变化
  
  关键点在于实现自己的OnPagerListener和继承PagerSlidingTabStrip.IconTabProvider

    private void updateIconStyle(int position) {
        LinearLayout tabsContainer = (LinearLayout) pstsIndicator.getChildAt(0);
        for (int i = 0; i < tabsContainer.getChildCount(); i++) {
            ImageButton imageButton = (ImageButton) tabsContainer.getChildAt(i);
            imageButton.setImageTintMode(PorterDuff.Mode.SRC_IN);
            if (i == position) {
                imageButton.setImageTintList(getResources().getColorStateList(R.color.ib_color_list));
            } else {
                imageButton.setImageTintList(getResources().getColorStateList(R.color.ib_color_list_normal));
            }
        }
    }

4. 写在最后的话
PagerSlidingTabStrip，总体来说简洁方便，如果开发者想集成自己的一些内容，比如说Indicator改成其他的形状，或者说想做到既有文字又有图片的效果，都可以自己修改代码来实现，比较的方便。

祝大家圣诞快乐。

Ending ~