1 IcsLinearLayout

首先看一下自定义的图标封装器，如果主题中配置了属性，则会在每个子view之间绘制分隔符

官方 support.v7 中已经添加了一个类android.support.v7.widget.LinearLayoutCompat 添加了对低版本 divider 的支持；

父类的构造通过setDividerDrawable为mDivider进行赋值，但是我们子类复写了这个方法，运行时调用的会是子类的方法，那么父类的这个方法自然就未执行，父类的mDivider为null了~~~；

关键应该是 private Drawable mDivider; 是private吧；

自定义的LinerLyout如何获取新的属性；

class IcsLinearLayout extends LinearLayout {
    private static final int[] LL = new int[] { // 要获取的属性集合
        /* 0 */ android.R.attr.divider,
        /* 1 */ android.R.attr.showDividers,
        /* 2 */ android.R.attr.dividerPadding,
    };
    private static final int LL_DIVIDER = ;// 属性集合中各属性的index
    private static final int LL_SHOW_DIVIDER = ;
    private static final int LL_DIVIDER_PADDING = ;

    private Drawable mDivider;
    private int mDividerWidth;
    private int mDividerHeight;
    private int mShowDividers;
    private int mDividerPadding;

    public IcsLinearLayout(Context context, int themeAttr) {
        super(context);
        // 第一个参数为null,因此只能从themeAttr即Activity的主题中去获取属性值了
        TypedArray a = context.obtainStyledAttributes(null, LL, themeAttr, );
        setDividerDrawable(a.getDrawable(IcsLinearLayout.LL_DIVIDER));
        mDividerPadding = a.getDimensionPixelSize(LL_DIVIDER_PADDING, );// 分隔符的上下与view的间隔
        mShowDividers = a.getInteger(LL_SHOW_DIVIDER, SHOW_DIVIDER_NONE);// 分隔符的类型如middle
        a.recycle();
    }

    public void setDividerDrawable(Drawable divider) {
        if (divider == mDivider) {
            return;
        }
        mDivider = divider;
        if (divider != null) {
            mDividerWidth = divider.getIntrinsicWidth();
            mDividerHeight = divider.getIntrinsicHeight();
        } else {
            mDividerWidth = ;
            mDividerHeight = ;
        }
        setWillNotDraw(divider == null); // 又看到了。。。
        requestLayout();
    }

    @Override
    protected void measureChildWithMargins(View child, int parentWidthMeasureSpec, int widthUsed, int parentHeightMeasureSpec, int heightUsed) { // 测试child的外边距
        final int index = indexOfChild(child);
        final int orientation = getOrientation();
        final LayoutParams params = (LayoutParams) child.getLayoutParams();
        if (hasDividerBeforeChildAt(index)) {// 满足时添加margin
            if (orientation == VERTICAL) {
                //Account for the divider by pushing everything up
                params.topMargin = mDividerHeight;
            } else {
                //Account for the divider by pushing everything left
                params.leftMargin = mDividerWidth;
            }
        }

        final int count = getChildCount();
        if (index == count - ) {
            if (hasDividerBeforeChildAt(count)) { //不满足
                if (orientation == VERTICAL) {
                    params.bottomMargin = mDividerHeight;
                } else {
                    params.rightMargin = mDividerWidth;
                }
            }
        }
        super.measureChildWithMargins(child, parentWidthMeasureSpec, widthUsed, parentHeightMeasureSpec, heightUsed);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        if (mDivider != null) {
            if (getOrientation() == VERTICAL) {
                drawDividersVertical(canvas);
            } else {
                drawDividersHorizontal(canvas);
            }
        }
        super.onDraw(canvas);
    }

    private void drawDividersVertical(Canvas canvas) {
        final int count = getChildCount();
        for (int i = ; i < count; i++) {
            final View child = getChildAt(i);
            if (child != null && child.getVisibility() != GONE) {
                if (hasDividerBeforeChildAt(i)) {
                    final android.widget.LinearLayout.LayoutParams lp = (android.widget.LinearLayout.LayoutParams) child.getLayoutParams();
                    final int top = child.getTop() - lp.topMargin/* - mDividerHeight*/;
                    drawHorizontalDivider(canvas, top);
                }
            }
        }
        if (hasDividerBeforeChildAt(count)) {
            final View child = getChildAt(count - );
            int bottom = ;
            if (child == null) {
                bottom = getHeight() - getPaddingBottom() - mDividerHeight;
            } else {
                //final LayoutParams lp = (LayoutParams) child.getLayoutParams();
                bottom = child.getBottom()/* + lp.bottomMargin*/;
            }
            drawHorizontalDivider(canvas, bottom);
        }
    }

    private void drawDividersHorizontal(Canvas canvas) {
        final int count = getChildCount();
        for (int i = ; i < count; i++) {
            final View child = getChildAt(i);
            if (child != null && child.getVisibility() != GONE) {
                if (hasDividerBeforeChildAt(i)) {
                    final android.widget.LinearLayout.LayoutParams lp = (android.widget.LinearLayout.LayoutParams) child.getLayoutParams();
                    // 计算分隔符的起始位置
                    final int left = child.getLeft() - lp.leftMargin/* - mDividerWidth*/;
                    drawVerticalDivider(canvas, left);//在margin的区域绘制drawable-Divider
                }
            }
        }
        if (hasDividerBeforeChildAt(count)) {//不满足
            final View child = getChildAt(count - );
            int right = ;
            if (child == null) {
                right = getWidth() - getPaddingRight() - mDividerWidth;
            } else { // 在所有图标的最右侧也绘制Divider
                //final LayoutParams lp = (LayoutParams) child.getLayoutParams();
                right = child.getRight()/* + lp.rightMargin*/;
            }
            drawVerticalDivider(canvas, right);
        }
    }

    private void drawHorizontalDivider(Canvas canvas, int top) {
        mDivider.setBounds(getPaddingLeft() + mDividerPadding, top,
                getWidth() - getPaddingRight() - mDividerPadding, top + mDividerHeight);
        mDivider.draw(canvas);
    }
    // 首先要设置绘制范围！！！可以看到mDividerPadding的使用
    private void drawVerticalDivider(Canvas canvas, int left) { 
        mDivider.setBounds(left, getPaddingTop() + mDividerPadding,
                left + mDividerWidth, getHeight() - getPaddingBottom() - mDividerPadding);
        mDivider.draw(canvas);
    }
    private boolean hasDividerBeforeChildAt(int childIndex) {
        if (childIndex ==  || childIndex == getChildCount()) {
          return false;
        }
        if ((mShowDividers & SHOW_DIVIDER_MIDDLE) != ) {
            boolean hasVisibleViewBefore = false;
            for (int i = childIndex - ; i >= ; i--) {
                if (getChildAt(i).getVisibility() != GONE) {
                    hasVisibleViewBefore = true;
                    break;
                }
            }
            return hasVisibleViewBefore;
        }
        return false;
    }
}

2 IconPageIndicator