如何在Android滑动选项卡布局中对齐活动选项卡中心

Question

我在android滑动标签布局+视图寻呼机中有12个项目。从左向右滑动时，所选标签应与播放商店中心相同。请帮我怎么做。在我的应用程序中，活动选项卡始终保留在屏幕上。

Answer 1

我的方法与Shripad Bhat解决方案略有不同，后者在幻灯片末尾弹出了标签。

这是我的解决方法......

对onPageScrolled方法的更改：

@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
    int tabStripChildCount = mTabStrip.getChildCount();
    if ((tabStripChildCount == 0) || (position < 0) || (position >= tabStripChildCount)) {
        return;
    }

    mTabStrip.onViewPagerPageChanged(position, positionOffset);

    View selectedTitle = mTabStrip.getChildAt(position);
    int selectedOffset = (selectedTitle == null) ? 0 : selectedTitle.getWidth();
    int nextTitlePosition = position + 1;
    View nextTitle = mTabStrip.getChildAt(nextTitlePosition);
    int nextOffset = (nextTitle == null) ? 0 : nextTitle.getWidth();
    int extraOffset = (int)(0.5F * (positionOffset * (float)(selectedOffset + nextOffset)));
    scrollToTab(position, extraOffset);

    if (mViewPagerPageChangeListener != null) {
        mViewPagerPageChangeListener.onPageScrolled(position, positionOffset, positionOffsetPixels);
    }
}

对scrollToTab方法的更改：

private int mLastScrollTo;

private void scrollToTab(int tabIndex, int positionOffset) {
    final int tabStripChildCount = mTabStrip.getChildCount();
    if (tabStripChildCount == 0 || tabIndex < 0 || tabIndex >= tabStripChildCount) {
        return;
    }

    View selectedChild = mTabStrip.getChildAt(tabIndex);
    if (selectedChild != null && selectedChild.getMeasuredWidth() != 0) {

        int targetScrollX = ((positionOffset + selectedChild.getLeft()) - getWidth() / 2) + selectedChild.getWidth() / 2;

        if (targetScrollX != mLastScrollTo) {
            scrollTo(targetScrollX, 0);
            mLastScrollTo = targetScrollX;
        }
    }
}

Answer 2

Google已为sliding tab layout提供了示例。但是在SlidingTabLayout类的实现中，它并不是为中心对齐选定的选项卡而设计的。我已修改滚动方法以使屏幕的选定/活动标签中心。这是代码更改：

班级名称：SlidingTabLayout

行号：241，scrollToTab {}

更新方法：

private void scrollToTab(int tabIndex, int positionOffset) {
    final int tabStripChildCount = mTabStrip.getChildCount();
    if (tabStripChildCount == 0 || tabIndex < 0 || tabIndex >= tabStripChildCount) {
        return;
    }

    View selectedChild = mTabStrip.getChildAt(tabIndex);
    if (selectedChild != null) {
        int targetScrollX = selectedChild.getLeft() + positionOffset;

        if (tabIndex > 0 || positionOffset > 0) {
            // If we're not at the first child and are mid-scroll, make sure we obey the offset
            targetScrollX -= (getWidth()-selectedChild.getWidth())/2;
        }

        scrollTo(targetScrollX, 0);
    }
}

Answer 3

也有这个问题。 tabLayout仅提供tabContentStart选项，需要双方：

public class CenteringTabLayout extends TabLayout {
public CenteringTabLayout(Context context) {
    super(context);
}

public CenteringTabLayout(Context context, AttributeSet attrs) {
    super(context, attrs);
}

public CenteringTabLayout(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
}

@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
    super.onLayout(changed, l, t, r, b);
    View firstTab = ((ViewGroup)getChildAt(0)).getChildAt(0);
    View lastTab = ((ViewGroup)getChildAt(0)).getChildAt(((ViewGroup)getChildAt(0)).getChildCount()-1);
    ViewCompat.setPaddingRelative(getChildAt(0), (getWidth()/2) - (firstTab.getWidth()/2),0,(getWidth()/2) - (lastTab.getWidth()/2),0);
}
}