SlidingTabLayout将活动标签锁定到中心

Question

我试图修改Google IO应用中的SlidingTabLayout，以便活动标签始终锁定在中间位置，就像最新的Google Play报亭和Foursquare版本一样。我将如何实现它？

Answer 1

我修改了SlidingTabLayout，以便包含选项卡的Horizo​​ntalScrollView根据ViewPager的滚动偏移量调整其填充。我花了3天才创造出可以接受的结果，我希望它也能帮助你！如果您有任何问题和/或改进，请评论！

SlidingTabLayout.java

/* 
* Copyright 2014 Google Inc. All rights reserved. 
* 
* Licensed under the Apache License, Version 2.0 (the "License"); 
* you may not use this file except in compliance with the License. 
* You may obtain a copy of the License at 
* 
*  http://www.apache.org/licenses/LICENSE-2.0 
* 
* Unless required by applicable law or agreed to in writing, software 
* distributed under the License is distributed on an "AS IS" BASIS, 
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
* See the License for the specific language governing permissions and 
* limitations under the License. 
*/ 

import android.animation.LayoutTransition; 
import android.content.Context; 
import android.graphics.Rect; 
import android.graphics.Typeface; 
import android.os.Build; 
import android.support.v4.view.PagerAdapter; 
import android.support.v4.view.ViewPager; 
import android.util.AttributeSet; 
import android.util.Log; 
import android.util.SparseArray; 
import android.util.TypedValue; 
import android.view.Gravity; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.view.ViewTreeObserver; 
import android.widget.HorizontalScrollView; 
import android.widget.LinearLayout; 
import android.widget.TextView; 

/** 
* To be used with ViewPager to provide a tab indicator component which give constant feedback as to 
* the user's scroll progress. 
* <p/> 
* To use the component, simply add it to your view hierarchy. Then in your 
* {@link android.app.Activity} or {@link android.support.v4.app.Fragment} call 
* {@link #setViewPager(ViewPager)} providing it the ViewPager this layout is being used for. 
* <p/> 
* The colors can be customized in two ways. The first and simplest is to provide an array of colors 
* via {@link #setSelectedIndicatorColors(int...)}. The 
* alternative is via the {@link TabColorizer} interface which provides you complete control over 
* which color is used for any individual position. 
* <p/> 
* The views used as tabs can be customized by calling {@link #setCustomTabView(int, int)}, 
* providing the layout ID of your custom layout. 
*/ 
public class SlidingTabLayout extends HorizontalScrollView { 
    /** 
    * Allows complete control over the colors drawn in the tab layout. Set with 
    * {@link #setCustomTabColorizer(TabColorizer)}. 
    */ 
    public interface TabColorizer { 

     /** 
     * @return return the color of the indicator used when {@code position} is selected. 
     */ 
     int getIndicatorColor(int position); 

    } 

    private static final int TAB_VIEW_PADDING_DIPS = 16; 
    private static final int TAB_VIEW_TEXT_SIZE_SP = 12; 

    private int mTabViewLayoutId; 
    private int mTabViewTextViewId; 
    private boolean mDistributeEvenly; 

    private ViewPager mViewPager; 
    private SparseArray<String> mContentDescriptions = new SparseArray<String>(); 
    private ViewPager.OnPageChangeListener mViewPagerPageChangeListener; 

    private final SlidingTabStrip mTabStrip; 

    public SlidingTabLayout(Context context) { 
     this(context, null); 
    } 

    public SlidingTabLayout(Context context, AttributeSet attrs) { 
     this(context, attrs, 0); 
    } 

    public SlidingTabLayout(Context context, AttributeSet attrs, int defStyle) { 
     super(context, attrs, defStyle); 

     // Disable the Scroll Bar 
     setHorizontalScrollBarEnabled(false); 
     // Make sure that the Tab Strips fills this View 
     setFillViewport(true); 

     mTabStrip = new SlidingTabStrip(context); 
     //mTabStrip.setVisibility(View.INVISIBLE); 
     addView(mTabStrip, LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT); 

     getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() { 
      @Override 
      public void onGlobalLayout() { 
       // Set spacer tab widths 
       View firstTab = mTabStrip.getChildAt(0); 
       int firstTabPadding = (getWidth() - mTabStrip.getChildAt(1).getMeasuredWidth())/2; 
       firstTab.setPadding(firstTabPadding, firstTab.getPaddingTop(), firstTab.getPaddingRight(), firstTab.getPaddingBottom()); 

       View lastTab = mTabStrip.getChildAt(mTabStrip.getChildCount() - 1); 
       int lastTabPadding = (getWidth() - mTabStrip.getChildAt(mTabStrip.getChildCount() - 2).getMeasuredWidth())/4; 
       lastTab.setPadding(lastTabPadding, 0, lastTabPadding, 0); 


       if (Build.VERSION.SDK_INT > Build.VERSION_CODES.ICE_CREAM_SANDWICH_MR1) 
        getViewTreeObserver().removeOnGlobalLayoutListener(this); 
       else 
        getViewTreeObserver().removeGlobalOnLayoutListener(this); 
      } 
     }); 
    } 

    /** 
    * Set the custom {@link TabColorizer} to be used. 
    * <p/> 
    * If you only require simple customisation then you can use 
    * {@link #setSelectedIndicatorColors(int...)} to achieve 
    * similar effects. 
    */ 
    public void setCustomTabColorizer(TabColorizer tabColorizer) { 
     mTabStrip.setCustomTabColorizer(tabColorizer); 
    } 

    public void setDistributeEvenly(boolean distributeEvenly) { 
     mDistributeEvenly = distributeEvenly; 
    } 

    /** 
    * Sets the colors to be used for indicating the selected tab. These colors are treated as a 
    * circular array. Providing one color will mean that all tabs are indicated with the same color. 
    */ 
    public void setSelectedIndicatorColors(int... colors) { 
     mTabStrip.setSelectedIndicatorColors(colors); 
    } 

    /** 
    * Set the {@link ViewPager.OnPageChangeListener}. When using {@link SlidingTabLayout} you are 
    * required to set any {@link ViewPager.OnPageChangeListener} through this method. This is so 
    * that the layout can update it's scroll position correctly. 
    * 
    * @see ViewPager#setOnPageChangeListener(ViewPager.OnPageChangeListener) 
    */ 
    public void setOnPageChangeListener(ViewPager.OnPageChangeListener listener) { 
     mViewPagerPageChangeListener = listener; 
    } 

    /** 
    * Set the custom layout to be inflated for the tab views. 
    * 
    * @param layoutResId Layout id to be inflated 
    * @param textViewId id of the {@link TextView} in the inflated view 
    */ 
    public void setCustomTabView(int layoutResId, int textViewId) { 
     mTabViewLayoutId = layoutResId; 
     mTabViewTextViewId = textViewId; 
    } 

    /** 
    * Sets the associated view pager. Note that the assumption here is that the pager content 
    * (number of tabs and tab titles) does not change after this call has been made. 
    */ 
    public void setViewPager(ViewPager viewPager) { 
     mTabStrip.removeAllViews(); 

     mViewPager = viewPager; 
     if (viewPager != null) { 
      viewPager.setOnPageChangeListener(new InternalViewPagerListener()); 
      populateTabStrip(); 
     } 
    } 

    /** 
    * Create a default view to be used for tabs. This is called if a custom tab view is not set via 
    * {@link #setCustomTabView(int, int)}. 
    */ 
    protected TextView createDefaultTabView(Context context) { 
     TextView textView = new TextView(context); 
     textView.setGravity(Gravity.CENTER); 
     textView.setTextSize(TypedValue.COMPLEX_UNIT_SP, TAB_VIEW_TEXT_SIZE_SP); 
     textView.setTypeface(Typeface.DEFAULT_BOLD); 
     textView.setLayoutParams(new LinearLayout.LayoutParams(
       ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT)); 

     TypedValue outValue = new TypedValue(); 
     getContext().getTheme().resolveAttribute(android.R.attr.selectableItemBackground, 
       outValue, true); 
     textView.setBackgroundResource(outValue.resourceId); 
     textView.setAllCaps(true); 

     int padding = (int) (TAB_VIEW_PADDING_DIPS * getResources().getDisplayMetrics().density); 
     textView.setPadding(padding, padding, padding, padding); 

     return textView; 
    } 

    private void populateTabStrip() { 
     final PagerAdapter adapter = mViewPager.getAdapter(); 
     final View.OnClickListener tabClickListener = new TabClickListener(); 

     for (int i = 0; i < adapter.getCount(); i++) { 
      View tabView = null; 
      TextView tabTitleView = null; 

      if (mTabViewLayoutId != 0) { 
       // If there is a custom tab view layout id set, try and inflate it 
       tabView = LayoutInflater.from(getContext()).inflate(mTabViewLayoutId, mTabStrip, 
         false); 
       tabTitleView = (TextView) tabView.findViewById(mTabViewTextViewId); 
      } 

      if (tabView == null) { 
       tabView = createDefaultTabView(getContext()); 
      } 

      if (tabTitleView == null && TextView.class.isInstance(tabView)) { 
       tabTitleView = (TextView) tabView; 
      } 

      if (mDistributeEvenly) { 
       LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) tabView.getLayoutParams(); 
       lp.width = 0; 
       lp.weight = 1; 
      } 

      tabTitleView.setText(adapter.getPageTitle(i)); 
      tabView.setOnClickListener(tabClickListener); 
      String desc = mContentDescriptions.get(i, null); 
      if (desc != null) { 
       tabView.setContentDescription(desc); 
      } 

      mTabStrip.addView(tabView); 
      if (i == mViewPager.getCurrentItem()) { 
       tabView.setSelected(true); 
      } 
     } 

     // First spacer tab 
     TextView firstTab = new TextView(getContext()); 
     mTabStrip.addView(firstTab, 0); 

     // Last spacer tab 
     TextView lastTab = new TextView(getContext()); 
     mTabStrip.addView(lastTab); 
    } 

    public void setContentDescription(int i, String desc) { 
     mContentDescriptions.put(i, desc); 
    } 

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

     if (positionOffset == -1) {// Not manual scroll. Do not animate. Just cut to tab and center. 
      if (tabIndex == 1) 
       positionOffset = 0; 
      else 
       positionOffset = mTabStrip.getChildAt(tabIndex).getWidth()/2 + mTabStrip.getChildAt(tabIndex + 1).getWidth()/2; 
     } 

     if (tabIndex == 1) // if tab number one, no need to calculate previously scrolled X 
      scrollTo(positionOffset, 0); 
     else { // If tab number is greater than 1, we need to calculate previously scrolled X 
      int previouslyScrolledX = 0; 

      // Simulate previously scrolled X by summing half of each of the previous tabs' width. 
      // Use 2 tabs per loop for correct simulation. 
      for (int i = 1; i < tabIndex; i++) { 
       previouslyScrolledX += mTabStrip.getChildAt(i).getWidth()/2; 
       previouslyScrolledX += mTabStrip.getChildAt(i + 1).getWidth()/2; 
      } 

      scrollTo(previouslyScrolledX + positionOffset, 0); 
     } 
    } 

    private class InternalViewPagerListener implements ViewPager.OnPageChangeListener { 
     private int mScrollState; 

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

      position++; // Offset position by 1 to make up for left blank tab 

      mTabStrip.onViewPagerPageChanged(position, positionOffset); 

      // Adding half of current tab's width & half of next tab's width and scrolling by that width will center next tab 
      int offsetToCenterNextTab = (mTabStrip.getChildAt(position).getWidth()/2) + (mTabStrip.getChildAt(position + 1).getWidth()/2); 

      scrollToTab(position, Math.round(offsetToCenterNextTab * positionOffset)); 

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

     @Override 
     public void onPageScrollStateChanged(int state) { 
      mScrollState = state; 

      if (mViewPagerPageChangeListener != null) { 
       mViewPagerPageChangeListener.onPageScrollStateChanged(state); 
      } 
     } 

     @Override 
     public void onPageSelected(int position) { 
      if (mScrollState == ViewPager.SCROLL_STATE_IDLE) { 
       mTabStrip.onViewPagerPageChanged(position, 0f); 
       scrollToTab(position, -1); 
      } 
      for (int i = 0; i < mTabStrip.getChildCount(); i++) { 
       mTabStrip.getChildAt(i).setSelected(position + 1 == i); 
      } 
      if (mViewPagerPageChangeListener != null) { 
       mViewPagerPageChangeListener.onPageSelected(position); 
      } 
     } 

    } 

    private class TabClickListener implements View.OnClickListener { 
     @Override 
     public void onClick(View selectedView) { 
      View lastSelectedView = null; 
      int selectedViewIndex = 0; 

      for (int i = 1; i < mTabStrip.getChildCount() - 1; i++) { 
       View currentViewInLoop = mTabStrip.getChildAt(i); 
       if (currentViewInLoop.isSelected()) { 
        lastSelectedView = currentViewInLoop; 
       } 

       if (selectedView == currentViewInLoop) { 
        selectedViewIndex = i - 1; 
       } 

       if (lastSelectedView != null && selectedViewIndex != 0) 
        break; 
      } 

      Rect tabContainerRect = new Rect(); 
      Rect lastSelectedTabRect = new Rect(); 

      getDrawingRect(tabContainerRect); 
      lastSelectedView.getHitRect(lastSelectedTabRect); 

      if (Rect.intersects(tabContainerRect, lastSelectedTabRect)) 
       mViewPager.setCurrentItem(selectedViewIndex); 
      else 
       mViewPager.setCurrentItem(selectedViewIndex, false); 
     } 
    } 
}