Android模仿摩拜单车车型选择按钮

个人感觉Tablayout里的indicator左右滑动和摩拜单车里按钮背景左右滑动很像，所以我的思路是修改Tablayout里indicator的位置和形状，把indicator的位置放在tab下面，并且修改indicator的形状为圆角矩形，那接下来就是具体实现啦

我采用的方法是改写material design下TabLayout的源码，修改的地方只有两处，都位于TabLayout内部类 

SlidingTabStrip 中

1、修改animateIndicatorToPosition()里的代码，这里主要处理按钮的背景左右移动的动画，

if (Math.abs(position - mSelectedPosition) <= 1) {
    // If the views are adjacent, we'll animate from edge-to-edge
    startLeft = mIndicatorLeft;
    startRight = mIndicatorRight;
} else {
    // Else, we'll just grow from the nearest edge
    final int offset = dpToPx(MOTION_NON_ADJACENT_OFFSET);
    if (position < mSelectedPosition) {
        // We're going end-to-start
        if (isRtl) {
            startLeft = startRight = targetLeft - offset;
        } else {
            startLeft = startRight = targetRight + offset;
        }
    } else {
        // We're going start-to-end
        if (isRtl) {
            startLeft = startRight = targetRight + offset;
        } else {
            startLeft = startRight = targetLeft - offset;
        }
    }
}

把以上这段代码浓缩成

startLeft = mIndicatorLeft;
startRight = mIndicatorRight;  

其余的都不要了

2.修改draw()方法里的代码，这里主要修改左右滑动背景的位置和形状

代码如下

@Override
public void draw(Canvas canvas) {
    // Thick colored underline below the current selection
    if (mIndicatorLeft >= 0 && mIndicatorRight > mIndicatorLeft) {
        /*canvas.drawRect(mIndicatorLeft, getHeight() - mSelectedIndicatorHeight,
                mIndicatorRight, getHeight(), mSelectedIndicatorPaint);*/
        int tabHeight=getChildAt(0).getHeight();
       // getHeight()-tabHeight+10;
        RectF oval3 = new RectF(mIndicatorLeft+50, getHeight()-tabHeight+30,
                mIndicatorRight-50, getHeight()-30);// 设置个新的长方形
        canvas.drawRoundRect(oval3, 60, 45, mSelectedIndicatorPaint);
    }
    super.draw(canvas);

}

besides，mSelectedIndicatorPaint这个画笔必须加上抗锯齿属性

mSelectedIndicatorPaint.setAntiAlias(true);

这样改完之后

setSelectedIndicatorHeight()设置indicator高度的方法就失效了，不过indicator的高度可以在draw里自己定义

来个效果图：

当然这种实现方法的缺点也有两个

1.要把tablayout以及相关类的源码复制出来，比较麻烦

2.无形中又多了好多个类啊，对APK大小敏感的同志慎用