隨著時間的推移現在的軟體要求顯示的內容越來越多，所以要在小的螢幕上能夠更好的顯示更多的內容，首先我們會想到底部選單欄，但是有時候像今日頭條新聞客戶端要顯示的內容太多，而且又想在主介面全部顯示出來，所以有加了頂部導航欄。

今日頭條頂部導航欄區域的主要部分是一個導航選單。導航選單是一組標籤的集合，在新聞客戶端中，每個標籤標示一個新聞類別，對應下面ViewPager控制元件的一個分頁面。當用戶在ViewPager區域滑動頁面時，對應的導航選單標籤也會相應的被選中，選中的標籤通過一個矩形紅框高亮顯示，紅框背景中的標籤文字變為白色，紅框外的區域標籤文字仍為灰色。當用戶直接在導航選單選中某個標籤時，ViewPager會自動的切換到對應的分頁面。在本文中導航選單作為一個單獨的UI控制元件實現，類名為CatagoryTabStrip，繼承自HorizontalScrollView，這樣就可以很容易的實現導航選單的左右滑動效果以及與下面ViewPager控制元件的聯動。

先看一下實現的效果對比：

頂部導航欄區域和ViewPager區域View層次結構


主介面佈局

<RelativeLayout android:id="@+id/main_layout" 
    android:background="@color/activity_bg_color" 
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent"
    xmlns:android="http://schemas.android.com/apk/res/android">
    <RelativeLayout android:id="@+id/title_bar" style="@style/main_title_bar_style">
        <FrameLayout android:id="@+id/top_head_container" 
            android:paddingLeft="10.0dip" 
            android:paddingRight="10.0dip" 
            android:layout_width="wrap_content"
             android:layout_height="fill_parent">
            <ImageView android:layout_gravity="center_vertical" 
                android:id="@+id/top_head" 
                android:contentDescription="@string/app_name"
                android:background="@drawable/bg_head" 
                android:src="@drawable/default_round_head"
                android:padding="2.0dip" 
                android:layout_width="@dimen/head_size" 
                android:layout_height="@dimen/head_size" 
                android:scaleType="fitXY" />
        </FrameLayout>
		<ImageView android:gravity="center" 
		    android:id="@+id/top_more" 
		    android:contentDescription="@string/app_name"
		    android:layout_width="wrap_content" 
		    android:layout_height="fill_parent" 
		    android:layout_marginRight="12.0dip" 
		    android:src="@drawable/right_drawer" 
		    android:scaleType="centerInside" 
		    android:layout_alignParentRight="true" 
		    android:layout_centerVertical="true" />
        <RelativeLayout android:id="@+id/title_click_layout" 
            android:paddingLeft="13.0dip" 
            android:layout_width="wrap_content" 
            android:layout_height="fill_parent" 
            android:layout_centerInParent="true">
            <FrameLayout android:id="@+id/title_parent" 
                android:layout_width="wrap_content" 
                android:layout_height="wrap_content" 
                android:layout_centerVertical="true">
                <ImageView android:layout_gravity="center" 
                    android:id="@+id/title_recent" 
                    android:contentDescription="@string/app_name"
                    android:layout_width="wrap_content" 
                    android:layout_height="wrap_content" 
                    android:src="@drawable/title" />
            </FrameLayout>
            <ImageView android:id="@+id/top_refresh" 
                android:contentDescription="@string/app_name"
                android:padding="3.0dip" 
                android:layout_width="wrap_content" 
                android:layout_height="wrap_content" 
                android:src="@drawable/refreshicon_titlebar" 
                android:layout_toRightOf="@id/title_parent" 
                android:layout_centerVertical="true" />
        </RelativeLayout>
	</RelativeLayout>
	
    <RelativeLayout android:id="@+id/category_layout" 
        android:background="@drawable/bg_category_bar" 
        android:layout_width="fill_parent" 
        android:layout_height="@dimen/top_category_height" 
        android:layout_below="@id/title_bar" >

		<ImageView android:id="@+id/icon_category" 
               android:layout_width="@dimen/top_category_height" 
               android:layout_height="@dimen/top_category_height" 
               android:src="@drawable/ic_category_expand"
               android:contentDescription="@string/app_name"
               android:scaleType="center" 
               android:layout_alignParentRight="true" 
               android:layout_centerVertical="true" />

		<LinearLayout android:layout_width="wrap_content" 
           android:layout_height="@dimen/top_category_height"
           android:layout_toLeftOf="@id/icon_category"
           android:layout_alignParentLeft="true" 
           android:layout_centerVertical="true">
           
			<com.rainsong.toutiaotabdemo.CategoryTabStrip 
                android:id="@+id/category_strip" 
                android:paddingLeft="6.0dip" 
                android:paddingRight="6.0dip" 
                android:clipToPadding="false" 
                android:layout_width="wrap_content" 
                android:layout_height="@dimen/top_category_height" />
        </LinearLayout>
    </RelativeLayout>
    <android.support.v4.view.ViewPager android:id="@+id/view_pager" 
        android:layout_width="fill_parent" 
        android:layout_height="fill_parent" 
        android:layout_below="@id/category_layout" />
</RelativeLayout>
 

在Activity中CatagoryTabStrip控制元件與ViewPager控制元件的聯合使用

MainActivity.java

package com.rainsong.toutiaotabdemo;

import java.util.ArrayList;
import java.util.List;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;

public class MainActivity extends FragmentActivity {
    private CategoryTabStrip tabs;
    private ViewPager pager;
    private MyPagerAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        tabs = (CategoryTabStrip) findViewById(R.id.category_strip);
        pager = (ViewPager) findViewById(R.id.view_pager);
        adapter = new MyPagerAdapter(getSupportFragmentManager());

        pager.setAdapter(adapter);

        tabs.setViewPager(pager);

    }

    public class MyPagerAdapter extends FragmentPagerAdapter {

        private final List<String> catalogs = new ArrayList<String>();

        public MyPagerAdapter(FragmentManager fm) {
            super(fm);
            catalogs.add(getString(R.string.category_hot));
            catalogs.add("\u672c\u5730");
            catalogs.add(getString(R.string.category_video));
            catalogs.add(getString(R.string.category_society));
            catalogs.add(getString(R.string.category_entertainment));
            catalogs.add(getString(R.string.category_tech));
            catalogs.add(getString(R.string.category_finance));
            catalogs.add(getString(R.string.category_military));
            catalogs.add(getString(R.string.category_world));
            catalogs.add(getString(R.string.category_image_ppmm));
            catalogs.add(getString(R.string.category_health));
            catalogs.add(getString(R.string.category_government));
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return catalogs.get(position);
        }

        @Override
        public int getCount() {
            return catalogs.size();
        }

        @Override
        public Fragment getItem(int position) {
            return NewsFragment.newInstance(position);
        }

    }

}
 

CatagoryTabStrip控制元件的實現程式碼

CategoryTabStrip.java

package com.rainsong.toutiaotabdemo;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.support.v4.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.TypedValue;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.HorizontalScrollView;
import android.widget.LinearLayout;
import android.widget.TextView;
public class CategoryTabStrip extends HorizontalScrollView {
    private LayoutInflater mLayoutInflater;
    private final PageListener pageListener = new PageListener();
    private ViewPager pager;
    private LinearLayout tabsContainer;
    private int tabCount;

    private int currentPosition = 0;
    private float currentPositionOffset = 0f;

    private Rect indicatorRect;

    private LinearLayout.LayoutParams defaultTabLayoutParams;

    private int scrollOffset = 10;
    private int lastScrollX = 0;

    private Drawable indicator;
    private TextDrawable[] drawables;
    private Drawable left_edge;
    private Drawable right_edge;

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

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

    public CategoryTabStrip(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        mLayoutInflater = LayoutInflater.from(context);
        drawables = new TextDrawable[3];
        int i = 0;
        while (i < drawables.length) {
            drawables[i] = new TextDrawable(getContext());
            i++;
        }

        indicatorRect = new Rect();

        setFillViewport(true);
        setWillNotDraw(false);

        // 標籤容器
        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);

        defaultTabLayoutParams = new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.MATCH_PARENT);
        // 繪製高亮區域作為滑動分頁指示器
        indicator = getResources().getDrawable(R.drawable.bg_category_indicator);
        // 左右邊界陰影效果
        left_edge = getResources().getDrawable(R.drawable.ic_category_left_edge);
        right_edge = getResources().getDrawable(R.drawable.ic_category_right_edge);
    }

    // 繫結與CategoryTabStrip控制元件對應的ViewPager控制元件，實現聯動
    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();
    }

    // 當附加在ViewPager介面卡上的資料發生變化時,應該呼叫該方法通知CategoryTabStrip重新整理資料
    public void notifyDataSetChanged() {
        tabsContainer.removeAllViews();
        tabCount = pager.getAdapter().getCount();
        for (int i = 0; i < tabCount; i++) {
            addTab(i, pager.getAdapter().getPageTitle(i).toString());
        }
    }

    // 新增一個標籤到導航選單
    private void addTab(final int position, String title) {
        ViewGroup tab = (ViewGroup)mLayoutInflater.inflate(R.layout.category_tab, this, false);
        TextView category_text = (TextView) tab.findViewById(R.id.category_text);
        category_text.setText(title);
        category_text.setGravity(Gravity.CENTER);
        category_text.setSingleLine();
        category_text.setFocusable(true);
        category_text.setTextColor(getResources().getColor(R.color.category_tab_text));
        tab.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                pager.setCurrentItem(position);
            }
        });
        tabsContainer.addView(tab, position, defaultTabLayoutParams);
    }

    // 計算滑動過程中矩形高亮區域的上下左右位置
    private void calculateIndicatorRect(Rect rect) {
        ViewGroup currentTab = (ViewGroup)tabsContainer.getChildAt(currentPosition);
        TextView category_text = (TextView) currentTab.findViewById(R.id.category_text);

        float left = (float) (currentTab.getLeft() + category_text.getLeft());
        float width = ((float) category_text.getWidth()) + left;

        if (currentPositionOffset > 0f && currentPosition < tabCount - 1) {
            ViewGroup nextTab = (ViewGroup)tabsContainer.getChildAt(currentPosition + 1);
            TextView next_category_text = (TextView) nextTab.findViewById(R.id.category_text);

            float next_left = (float) (nextTab.getLeft() + next_category_text.getLeft());
            left = left * (1.0f - currentPositionOffset) + next_left * currentPositionOffset;
            width = width * (1.0f - currentPositionOffset) + currentPositionOffset * (((float) next_category_text.getWidth()) + next_left);
        }

        rect.set(((int) left) + getPaddingLeft(), getPaddingTop() + currentTab.getTop() + category_text.getTop(),
                ((int) width) + getPaddingLeft(), currentTab.getTop() + getPaddingTop() + category_text.getTop() + category_text.getHeight());
    }

    // 計算滾動範圍
    private int getScrollRange() {
        return getChildCount() > 0 ? Math.max(0, getChildAt(0).getWidth() - getWidth() + getPaddingLeft() + getPaddingRight()) : 0;
    }

    // CategoryTabStrip與ViewPager聯動邏輯
    private void scrollToChild(int position, int offset) {
        if (tabCount == 0) {
            return;
        }

        calculateIndicatorRect(indicatorRect);
        int newScrollX = lastScrollX;
        if (indicatorRect.left < getScrollX() + scrollOffset) {
            newScrollX = indicatorRect.left - scrollOffset;
        } else if (indicatorRect.right > getScrollX() + getWidth() - scrollOffset) {
            newScrollX = indicatorRect.right - getWidth() + scrollOffset;
        }
        if (newScrollX != lastScrollX) {
            lastScrollX = newScrollX;
            scrollTo(newScrollX, 0);
        }
    }

    // 自定義繪圖
    @Override
    public void draw(Canvas canvas) {
        super.draw(canvas);

        // 繪製高亮背景矩形紅框
        calculateIndicatorRect(indicatorRect);
        if(indicator != null) {
            indicator.setBounds(indicatorRect);
            indicator.draw(canvas);
        }

        // 繪製背景紅框內標籤文字
        int i = 0;
        while (i < tabsContainer.getChildCount()) {
            if (i < currentPosition - 1 || i > currentPosition + 1) {
                i++;
            } else {
                ViewGroup tab = (ViewGroup)tabsContainer.getChildAt(i);
                TextView category_text = (TextView) tab.findViewById(R.id.category_text);
                if (category_text != null) {
                    TextDrawable textDrawable = drawables[i - currentPosition + 1];
                    int save = canvas.save();
                    calculateIndicatorRect(indicatorRect);
                    canvas.clipRect(indicatorRect);
                    textDrawable.setText(category_text.getText());
                    textDrawable.setTextSize(0, category_text.getTextSize());
                    textDrawable.setTextColor(getResources().getColor(R.color.category_tab_highlight_text));
                    int left = tab.getLeft() + category_text.getLeft() + (category_text.getWidth() - textDrawable.getIntrinsicWidth()) / 2 + getPaddingLeft();
                    int top = tab.getTop() + category_text.getTop() + (category_text.getHeight() - textDrawable.getIntrinsicHeight()) / 2 + getPaddingTop();
                    textDrawable.setBounds(left, top, textDrawable.getIntrinsicWidth() + left, textDrawable.getIntrinsicHeight() + top);
                    textDrawable.draw(canvas);
                    canvas.restoreToCount(save);
                }
                i++;
            }
        }

        // 繪製左右邊界陰影效果
        i = canvas.save();
        int top = getScrollX();
        int height = getHeight();
        int width = getWidth();
        canvas.translate((float) top, 0.0f);
        if (left_edge == null || top <= 0) {
            if (right_edge == null || top >= getScrollRange()) {
                canvas.restoreToCount(i);
            }
            right_edge.setBounds(width - right_edge.getIntrinsicWidth(), 0, width, height);
            right_edge.draw(canvas);
            canvas.restoreToCount(i);
        }
        left_edge.setBounds(0, 0, left_edge.getIntrinsicWidth(), height);
        left_edge.draw(canvas);
        if (right_edge == null || top >= getScrollRange()) {
            canvas.restoreToCount(i);
        }
        right_edge.setBounds(width - right_edge.getIntrinsicWidth(), 0, width, height);
        right_edge.draw(canvas);
        canvas.restoreToCount(i);
    }

    private class PageListener implements OnPageChangeListener {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
            currentPosition = position;
            currentPositionOffset = positionOffset;

            scrollToChild(position, (int) (positionOffset * tabsContainer.getChildAt(position).getWidth()));
            invalidate();
        }

        @Override
        public void onPageScrollStateChanged(int state) {
            if (state == ViewPager.SCROLL_STATE_IDLE) {
                if(pager.getCurrentItem() == 0) {
                    // 滑動到最左邊
                    scrollTo(0, 0);
                } else if (pager.getCurrentItem() == tabCount - 1) {
                    // 滑動到最右邊
                    scrollTo(getScrollRange(), 0);
                } else {
                    scrollToChild(pager.getCurrentItem(), 0);
                }
            }
        }

        @Override
        public void onPageSelected(int position) {
        }
    }
}