最近有很多人微信底部的变色卡片导航是怎么做的，我在网上看了好几个例子，都是效果接近，都存有一些差异，自己琢磨也做了一个，几乎99%的还原，效果还不错吧

仔细观察微信图片，发现他有两部分内容，外面的边框和里面的内容，内容的颜色由绿变为透明，这部分可以直接改变透明度，外面的边框，颜色在灰色和绿色之间变化，就不能简单的改变透明度了，ImageView的tint 为我们提供了可行方案，tint可以为图标着色，既可以在xml中,也可以在代码中设置，一共有16中模式，分别为

在xml中设置：直接添加tint属性，选择tintMode模式

 <ImageView
            android:id="@+id/green"
            android:layout_width="50dp"
            android:layout_height="50dp"
            android:src="@mipmap/green"
            android:tint="@color/colorPrimary"
            android:tintMode="src_in"/>

mGreenImageView.setColorFilter(color,mode) mode参数类型  PorterDuff.Mode

为了理解不同颜色，不同透明度的图片在设置不同的tint模式，不同的颜色后的变化，写了一个demo，四个滑动条分别代表了颜色的alpha，R、G、B值，改变滑动为止，通过Color.argb(alpha,red,green,blue)动态组合出不同的颜色，通过Spinner选择不同的模式，通过给图像设置模式和不同的tint颜色，展示不同的效果，观察结果，可以知道给imageview设置tint后，图标最后展示出来的颜色不仅和设置的模式相关，还有图像的原有颜色和透明度相关。具体是怎样的相关性，语言描述不清，请自行体会。

选了实心绿，透明白，实心紫红的三张图片进行测试验证

界面很简单，只是一些基本的控件，代码如下

public class SimpleActivity extends Activity {
    private ImageView mGreenImageView;
    private ImageView mTransparentImageView;
    private ImageView mRedImageView;
    //透明度滑动条
    private SeekBar mTransparentSeekBar;
    private Spinner mSpinner;
    //红色滑动条
    private SeekBar mRedSeekBar;
    //绿色滑动条
    private SeekBar mGreenSeekBar;
    //蓝色滑动条
    private SeekBar mBlueSeekBar;
    private TextView mTextView;
    private SeekBar.OnSeekBarChangeListener mOnSeekBarChangeListener; //滑动条监听器
    //PorterDuff.Mode 列表
    private static final PorterDuff.Mode[] MODES = new PorterDuff.Mode[]{
            PorterDuff.Mode.ADD,
            PorterDuff.Mode.CLEAR,
            PorterDuff.Mode.DARKEN,
            PorterDuff.Mode.DST,
            PorterDuff.Mode.DST_ATOP,
            PorterDuff.Mode.DST_IN,
            PorterDuff.Mode.DST_OUT,
            PorterDuff.Mode.DST_OVER,
            PorterDuff.Mode.LIGHTEN,
            PorterDuff.Mode.MULTIPLY,
            PorterDuff.Mode.OVERLAY,
            PorterDuff.Mode.SCREEN,
            PorterDuff.Mode.SRC,
            PorterDuff.Mode.SRC_ATOP,
            PorterDuff.Mode.SRC_IN,
            PorterDuff.Mode.SRC_OUT,
            PorterDuff.Mode.SRC_OVER,
            PorterDuff.Mode.XOR
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_simple);
        mGreenImageView = (ImageView) findViewById(R.id.green);
        mTransparentImageView= (ImageView) findViewById(R.id.transparent);
        mRedImageView= (ImageView) findViewById(R.id.red);
        mTextView= (TextView) findViewById(R.id.text);
        mTransparentSeekBar = (SeekBar) findViewById(R.id.alpha_seekbar);
        mRedSeekBar= (SeekBar) findViewById(R.id.red_seekbar);
        mGreenSeekBar= (SeekBar) findViewById(R.id.green_seekbar);
        mBlueSeekBar= (SeekBar) findViewById(R.id.blue_seekbar);
        mSpinner= (Spinner) findViewById(R.id.spinner);
        SpinnerAdapter spinnerAdapter=ArrayAdapter.createFromResource(SimpleActivity.this,R.array.blend_modes, android.R.layout.simple_list_item_1);
        mSpinner.setAdapter(spinnerAdapter);
        initListener();


    }

    private void initListener() {
        mSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                updateImage(getRGBColor(),getMode());
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {

            }
        });
        mOnSeekBarChangeListener=new SeekBar.OnSeekBarChangeListener() {
            @Override
            public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
                updateImage(getRGBColor(),getMode());
            }

            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {

            }

            @Override
            public void onStopTrackingTouch(SeekBar seekBar) {

            }
        };
        mTransparentSeekBar.setOnSeekBarChangeListener(mOnSeekBarChangeListener);
        mRedSeekBar.setOnSeekBarChangeListener(mOnSeekBarChangeListener);
        mGreenSeekBar.setOnSeekBarChangeListener(mOnSeekBarChangeListener);
        mBlueSeekBar.setOnSeekBarChangeListener(mOnSeekBarChangeListener);
    }

    private PorterDuff.Mode getMode() {
        return MODES[mSpinner.getSelectedItemPosition()];
    }

    /**
     * @return 根据ARGB颜色滑动条的数值计算颜色值
     */
    private int getRGBColor() {
        int alpha= mTransparentSeekBar.getProgress();
        int red=mRedSeekBar.getProgress();
        int green=mGreenSeekBar.getProgress();
        int blue=mBlueSeekBar.getProgress();
        return Color.argb(alpha,red,green,blue);
    }

    /**
     * 更新颜色 模式
     * @param color
     * @param mode
     */
    private void updateImage(int color,  PorterDuff.Mode mode ) {
        mGreenImageView.setColorFilter(color,mode);
        mTransparentImageView.setColorFilter(color,mode);
        mRedImageView.setColorFilter(color,mode);
        mTextView.setTextColor(color);
    }
}

现在已经介绍了ImageView中tint使用的基础知识，下面我们就开始我们标题中所说的微信导航栏效果，我用肉眼能识别精度仔细观察了微信，发现微信主要有两个部分，外面的框和里面的内容，从上一页滑到下一页，滑动到一半前，上一页的外框保持不变，内容由绿色变为透明，下一页的外框由灰色变为绿色，滑到一半后，上一页的外框由绿色变为灰色，下一页的内容由透明变为绿色，现象已经描述的很清楚了，现在我们用两张图片实现效果，一张边框，一张内容，使用tint 的src_in模式，可以把任意纯色图片喜欢的颜色，为了方便，内容只改变透明度，选为绿色，边框任意，监听ViewPager滑动状态，根据ViewPager便宜量，计算当前颜色值，tint着色渲染

布局文件

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    tools:context="com.why.drawabletinttest.PagerActivity">
    <android.support.v4.view.ViewPager
        android:layout_width="match_parent"
        android:id="@+id/pager_view"
        android:layout_height="match_parent"></android.support.v4.view.ViewPager>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom">
        <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:gravity="center_horizontal"
            android:orientation="vertical">
            <FrameLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:gravity="center_horizontal"
                >
                <ImageView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:id="@+id/image1_white"/>
                <ImageView
                    android:id="@+id/image1_top"
                    android:layout_width="40dp"
                    android:layout_height="40dp"
                    android:tint="@android:color/transparent"
                    android:layout_gravity="center_horizontal"
                    android:src="@mipmap/chats_green"/>
                <ImageView
                    android:id="@+id/image1"
                    android:layout_width="40dp"
                    android:layout_height="40dp"
                    android:tint="@android:color/transparent"
                    android:layout_gravity="center_horizontal"
                    android:src="@mipmap/chats"/>
            </FrameLayout>
            <TextView
                android:id="@+id/text1"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="晴川"/>
        </LinearLayout>

        <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:gravity="center_horizontal"
            android:orientation="vertical">
            <FrameLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:gravity="center_horizontal"
                >
                <ImageView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:id="@+id/image2_white"/>
                <ImageView
                    android:id="@+id/image2_top"
                    android:layout_width="40dp"
                    android:layout_height="40dp"
                    android:tint="@android:color/transparent"
                    android:layout_gravity="center_horizontal"
                    android:src="@mipmap/contacts_green"/>
                <ImageView
                    android:id="@+id/image2"
                    android:layout_width="40dp"
                    android:layout_height="40dp"
                    android:layout_gravity="center_horizontal"
                    android:src="@mipmap/contacts"/>

            </FrameLayout>
            <TextView
                android:id="@+id/text2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="芳草"/>

        </LinearLayout>

        <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:gravity="center_horizontal"
            android:orientation="vertical"
            >
            <FrameLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:gravity="center_horizontal">
                <ImageView
                    android:id="@+id/image3_top"
                    android:layout_width="40dp"
                    android:layout_height="40dp"
                    android:tint="@android:color/transparent"
                    android:layout_gravity="center_horizontal"
                    android:src="@mipmap/discover_green"/>

                />
                <ImageView
                    android:layout_gravity="center_horizontal"
                    android:id="@+id/image3"
                    android:layout_width="40dp"
                    android:layout_height="40dp"
                    android:src="@mipmap/discover"
                    />
                <ImageView
                    android:layout_gravity="center_horizontal"
                    android:id="@+id/image3_white"
                    android:layout_width="40dp"
                    android:layout_height="40dp"
                    android:tint="@android:color/white"
                    android:src="@mipmap/discover_white"/>

            </FrameLayout>
            <TextView
                android:id="@+id/text3"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="孤城"/>
        </LinearLayout>
    </LinearLayout>

</FrameLayout>

Activity代码

package com.why.drawabletinttest;

import android.app.Activity;
import android.graphics.Color;
import android.graphics.PorterDuff;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.os.Bundle;
import android.util.Log;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

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

/**
 * @author wanghuayan
 */
public class PagerActivity extends Activity {
    private ViewPager mViewPager;
    //灰色以及相对应的RGB值
    private int mGrayColor;
    private int mGrayRed;
    private int mGrayGreen;
    private int mGrayBlue;
    //灰色以及相对应的RGB值
    private int mGreenColor;
    private int mGreenRed;
    private int mGreenGreen;
    private int mGreenBlue;
    private List<TextView> textViews;//viewpager中适配的 item
    private ImageView[] mBorderimageViews;  //外部的边框
    private ImageView[] mContentImageViews; //内部的内容
    private ImageView[] mWhiteImageViews;  //发现上面的白色部分
    private TextView[] mTitleViews;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_pager);
        initColor();
        mViewPager = (ViewPager) findViewById(R.id.pager_view);
        ImageView imageView1 = (ImageView) findViewById(R.id.image1);
        ImageView imageView2 = (ImageView) findViewById(R.id.image2);
        ImageView imageView3 = (ImageView) findViewById(R.id.image3);
        mBorderimageViews = new ImageView[]{imageView1, imageView2, imageView3};
        TextView textView = new TextView(PagerActivity.this);
        TextView textView1 = new TextView(PagerActivity.this);
        TextView textView2 = new TextView(PagerActivity.this);
        textViews = new ArrayList<>();
        textViews.add(textView);
        textViews.add(textView1);
        textViews.add(textView2);

        ImageView topImageView1 = (ImageView) findViewById(R.id.image1_top);
        ImageView topImageView2 = (ImageView) findViewById(R.id.image2_top);
        ImageView topImageView3 = (ImageView) findViewById(R.id.image3_top);
        mContentImageViews = new ImageView[]{topImageView1, topImageView2, topImageView3};


        ImageView whiteImageView1 = (ImageView) findViewById(R.id.image1_white);
        ImageView whiteImageView2 = (ImageView) findViewById(R.id.image2_white);
        ImageView whiteImageView3 = (ImageView) findViewById(R.id.image3_white);
        mWhiteImageViews = new ImageView[]{whiteImageView1, whiteImageView2, whiteImageView3};


        TextView titileView1 = (TextView) findViewById(R.id.text1);
        TextView titileView2 = (TextView) findViewById(R.id.text2);
        TextView titileView3 = (TextView) findViewById(R.id.text3);
        mTitleViews = new TextView[]{titileView1, titileView2, titileView3};


        ItemPagerAdapter adapter = new ItemPagerAdapter(textViews);
        mViewPager.setAdapter(adapter);
        setSelection(0);


        mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
                if (positionOffset > 0) {
                    if (positionOffset < 0.5) {
                        //  滑动到一半前，上一页的边框保持绿色不变，下一页的边框由灰色变为绿色
                        mBorderimageViews[position].setColorFilter(mGreenColor, PorterDuff.Mode.SRC_IN);
                        mBorderimageViews[position + 1].setColorFilter(getGrayToGreen(positionOffset), PorterDuff.Mode.SRC_IN);
                        //   上一页的内容保持由实心变为透明，下一页的内容保持透明
                        mContentImageViews[position].setAlpha((1 - 2 * positionOffset));
                        mContentImageViews[position + 1].setAlpha(0f);
                        //文字颜色变化
                        mTitleViews[position].setTextColor(mGreenColor);
                        mTitleViews[position + 1].setTextColor(getGrayToGreen(positionOffset));

                    } else {
                        //滑动到一半后，上一页的边框由绿变为灰色，，下一页边框保持绿色不变
                        mBorderimageViews[position].setColorFilter(getGreenToGray(positionOffset), PorterDuff.Mode.SRC_IN);
                        mBorderimageViews[position + 1].setColorFilter(mGreenColor, PorterDuff.Mode.SRC_IN);
                        //上一页的内容保持透明，下一页的内容由透明变为实心绿色
                        mContentImageViews[position].setAlpha(0f);
                        mContentImageViews[position + 1].setAlpha(2 * positionOffset - 1);
                        mTitleViews[position].setTextColor(getGreenToGray(positionOffset));
                        mTitleViews[position + 1].setTextColor(mGreenColor);
                        if (position > 0.8) {
                            mWhiteImageViews[position + 1].setVisibility(View.VISIBLE);
                            mWhiteImageViews[position + 1].setAlpha(10 * positionOffset - 8);
                        } else {
                            mWhiteImageViews[position + 1].setVisibility(View.GONE);
                        }
                    }
                }


            }

            @Override
            public void onPageSelected(int position) {
                setSelection(position);

            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });


    }

    /**
     * 设置索引  当前导航页边框绿色，内容实心绿，其他页边框灰色，内容透明
     *
     * @param position
     */
    private void setSelection(int position) {
        for (int i = 0; i < mBorderimageViews.length; i++) {
            if (i == position) {
                mBorderimageViews[i].setColorFilter(mGreenColor, PorterDuff.Mode.SRC_IN);
                mContentImageViews[i].setAlpha(1f);
                mWhiteImageViews[i].setVisibility(View.VISIBLE);
                mTitleViews[i].setTextColor(mGreenColor);
            } else {
                mBorderimageViews[i].setColorFilter(mGrayColor, PorterDuff.Mode.SRC_IN);
                mContentImageViews[i].setAlpha(0f);
                mWhiteImageViews[i].setVisibility(View.GONE);
                mTitleViews[i].setTextColor(mGrayColor);
            }
        }
    }


    private void initColor() {
        mGrayColor = getResources().getColor(R.color.gray);
        mGrayRed = Color.red(mGrayColor);
        mGrayGreen = Color.green(mGrayColor);
        mGrayBlue = Color.blue(mGrayColor);
        mGreenColor = getResources().getColor(R.color.green);
        mGreenRed = Color.red(mGreenColor);
        mGreenGreen = Color.green(mGreenColor);
        mGreenBlue = Color.blue(mGreenColor);
    }

    /**
     * 偏移量在 0——0.5区间 ，左边一项颜色不变，右边一项颜色从灰色变为绿色，根据两点式算出RGB变化函数，组合出颜色
     *
     * @param positionOffset
     * @return
     */
    private int getGrayToGreen(float positionOffset) {
        int red = (int) (positionOffset * (mGreenRed - mGrayRed) * 2 + mGrayRed);
        int green = (int) (positionOffset * (mGreenGreen - mGrayGreen) * 2 + mGrayGreen);
        int blue = (int) ((positionOffset) * (mGreenBlue - mGrayBlue) * 2 + mGrayBlue);
        Log.d("why ", "#### " + red + "  " + green + "  " + blue);
        return Color.argb(255, red, green, blue);
    }

    /**
     * 偏移量在 0.5--1 区间，颜色从绿色变成灰色，根据两点式算出变化RGB随偏移量变化函数，组合出颜色
     *
     * @param positionOffset
     * @return
     */
    private int getGreenToGray(float positionOffset) {
        int red = (int) (positionOffset * (mGrayRed - mGreenRed) * 2 + 2 * mGreenRed - mGrayRed);
        int green = (int) (positionOffset * (mGrayGreen - mGreenGreen) * 2 + 2 * mGreenGreen - mGrayGreen);
        int blue = (int) (positionOffset * (mGrayBlue - mGreenBlue) * 2 + 2 * mGreenBlue - mGrayBlue);
        Log.d("why ", "#### " + red + "  " + green + "  " + blue);
        return Color.argb(255, red, green, blue);
    }


    /**
     * viewpager适配器
     */
    class ItemPagerAdapter extends PagerAdapter {
        List<TextView> list;

        public ItemPagerAdapter(List<TextView> views) {
            list = views;
        }

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

        @Override
        public boolean isViewFromObject(View arg0, Object arg1) {
            return arg0 == arg1;
        }

        @Override
        public Object instantiateItem(ViewGroup container, int position) {
            switch (position) {
                case 0:
                    list.get(position).setText("晴川历历汉阳树");
                    break;
                case 1:
                    list.get(position).setText("芳草萋萋鹦鹉洲");
                    break;
                case 2:
                    list.get(position).setText("长烟落日孤城闭");
                    break;
            }
            list.get(position).setGravity(Gravity.CENTER);

            container.addView(list.get(position), 0);
            return list.get(position);
        }

        @Override
        public void destroyItem(ViewGroup container, int position, Object object) {
            container.removeView(list.get(position));
        }
    }
}

到此为止，微信滑动导航卡就完成了，不需要自定义，用简单的imageview就可以完成，效果也是非常好，可能有点难度的就是滑动过程中颜色的计算，就是高中的两点式计算，这里换个马甲，有人可能有些迷惑。颜色可以分解为RGB三色，分别算出当前偏移量上的RGB，在组合在一起。举个例子哇，在0.5到1之间，颜色从 绿色变为灰色，列个函数（color-绿）/(position-0.5)=(灰-绿)/(1-0.5)，算出color和 position函数，置换为对应的RGB变化。

demo下载地址

android高仿微信底部渐变导航栏