拆PagerSlidingTabStrip

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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。

JuheNews GankIOClient

PagerSlidingTabStrip源码地址:

https://github.com/astuetz/PagerSlidingTabStrip

使用方法

dependencies {
    compile 'com.astuetz:pagerslidingtabstrip:1.0.1'
}
    <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"/>
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);
    }
}

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 这里写图片描述

  1. PagerSlidingTabStrip.java类结构 getter and setter 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。 这里写图片描述

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
变量意义
ATTRS引用Android系统的两个属性,文本字体大小和字体颜色
pageListener内部使用的OnPagerChangeListener,通过setViewPager实现和ViewPager的联动
delegatePageListener暴露给开发者的接口,类本身使用到了两个OnPageChangeListener,一个用来实现自己的逻辑,而这个则是留给开发者实现自己需要针对ViewPager的页面变化的逻辑
tabsContainer内部容器,用户所见文本指示器和图标指示器的父节点,所以,如果需要针对文本指示器或者是图标指示器做什么操作,通过这个查找孩子节点即可

这里写图片描述

	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);
		}
	}
	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;
		}
	}
	@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);
		}
	}
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;
	}
  1. PagerSlidingTabStrip综合用法
 @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));
            }
        }
    }

这里写图片描述

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));
            }
        }
    }
  1. 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。