Android 微信6.1 tab栏图标和字体颜色渐变的实现

相信大家都见到了微信图标颜色渐变的过程，是不是感觉很牛逼？不得不说微信团队确实是很厉害的团队，不管是从设计还是开发人员。

今天我带大家来看看，微信 tab 栏图标和字体颜色渐变的过程。先上图吧！今天学了一招制作 gif 动态图的快捷方法。刚好用的上，以前一直想写点什么东西，

苦于一直不知道怎么生成动态图，现在终于学会了，哈哈，让我偷偷的乐一会。额，还是上图吧。。。

好了，效果图也看到了，那么我也就不多啰嗦了，直接进入主题，看代码

[java] view plain copy
package moon.wechat.view; 
import Android.content.Context; 
import android.graphics.Bitmap; 
import android.graphics.BitmapFactory; 
import android.graphics.canvas; 
import android.graphics.Paint; 
import android.graphics.Rect; 
import android.util.AttributeSet; 
import android.util.TypedValue; 
import android.view.View; 
 
public class TabItem extends View { 
   
  private int mTextSize ; 
   
  private int mTextColorSelect ; 
   
  private int mTextColorNORMal; 
   
  private Paint mTextPaintNormal; 
   
  private Paint mTextPaintSelect; 
   
  private int mViewHeight, mViewWidth; 
   
  private String mTextValue ; 
   
  private Bitmap mIconNormal; 
   
  private Bitmap mIconSelect; 
   
  private Rect mBoundText; 
   
  private Paint mIconPaintSelect; 
   
  private Paint mIconPaintNormal; 
  public TabItem(Context context) { 
    this(context, null); 
  } 
  public TabItem(Context context, AttributeSet attrs) { 
    this(context, attrs, 0); 
  } 
  public TabItem(Context context, AttributeSet attrs, int defStyleAttr) { 
    super(context, attrs, defStyleAttr); 
    initView(); 
    initText(); 
  } 
   
  private void initView() { 
    mBoundText = new Rect(); 
  } 
   
  private void initText() { 
    mTextPaintNormal = new Paint(); 
    mTextPaintNormal.setTextSize(TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, mTextSize, getResources().getDisplayMetrics())); 
    mTextPaintNormal.setColor(mTextColorNormal); 
    mTextPaintNormal.setAntiAlias(true); 
    mTextPaintNormal.setAlpha(0xff); 
    mTextPaintSelect = new Paint(); 
    mTextPaintSelect.setTextSize(TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, mTextSize, getResources().getDisplayMetrics())); 
    mTextPaintSelect.setColor(mTextColorSelect); 
    mTextPaintSelect.setAntiAlias(true); 
    mTextPaintSelect.setAlpha(0); 
    mIconPaintSelect = new Paint(Paint.ANTI_ALIAS_FLAG) ; 
    mIconPaintSelect.setAlpha(0); 
    mIconPaintNormal = new Paint(Paint.ANTI_ALIAS_FLAG) ; 
    mIconPaintNormal.setAlpha(0xff); 
  } 
   
  private void measureText() { 
    mTextPaintNormal.getTextBounds(mTextValue, 0, mTextValue.length(), mBoundText); 
  } 
   
  @Override 
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { 
    int widthMode = MeasureSpec.getMode(widthMeasureSpec); 
    int heightMode = MeasureSpec.getMode(heightMeasureSpec); 
    int widthSize = MeasureSpec.getSize(widthMeasureSpec); 
    int heightSize = MeasureSpec.getSize(heightMeasureSpec); 
    int width = 0, height = 0; 
    measureText(); 
    int contentWidth = Math.max(mBoundText.width(), mIconNormal.getWidth()); 
    int desiredWidth = getPaddingLeft() + getPaddingRight() + contentWidth; 
    switch (widthMode) { 
      case MeasureSpec.AT_MOST: 
        width = Math.min(widthSize, desiredWidth); 
        break; 
      case MeasureSpec.EXACTLY: 
        width = widthSize; 
        break; 
      case MeasureSpec.UNSPECIFIED: 
        width = desiredWidth; 
        break; 
    } 
    int contentHeight = mBoundText.height() + mIconNormal.getHeight(); 
    int desiredHeight = getPaddingTop() + getPaddingBottom() + contentHeight; 
    switch (heightMode) { 
      case MeasureSpec.AT_MOST: 
        height = Math.min(heightSize, desiredHeight); 
        break; 
      case MeasureSpec.EXACTLY: 
        height = heightSize; 
        break; 
      case MeasureSpec.UNSPECIFIED: 
        height = contentHeight; 
        break; 
    } 
    setMeasuredDimension(width, height); 
    mViewWidth = getMeasuredWidth() ; 
    mViewHeight = getMeasuredHeight() ; 
  } 
  @Override 
  protected void onDraw(Canvas canvas) { 
    drawBitmap(canvas) ; 
    drawText(canvas) ; 
  } 
   
  private void drawBitmap(Canvas canvas) { 
    int left = (mViewWidth - mIconNormal.getWidth())/2 ; 
    int top = (mViewHeight - mIconNormal.getHeight() - mBoundText.height()) /2 ; 
    canvas.drawBitmap(mIconNormal, left, top ,mIconPaintNormal); 
    canvas.drawBitmap(mIconSelect, left, top , mIconPaintSelect); 
  } 
   
  private void drawText(Canvas canvas) { 
    float x = (mViewWidth - mBoundText.width())/2.0f ; 
    float y = (mViewHeight + mIconNormal.getHeight() + mBoundText.height()) /2.0F ; 
    canvas.drawText(mTextValue,x,y, mTextPaintNormal); 
    canvas.drawText(mTextValue,x,y, mTextPaintSelect); 
  } 
  public void setTextSize(int textSize) { 
    this.mTextSize = textSize; 
    mTextPaintNormal.setTextSize(textSize); 
    mTextPaintSelect.setTextSize(textSize); 
  } 
  public void setTextColorSelect(int mTextColorSelect) { 
    this.mTextColorSelect = mTextColorSelect; 
    mTextPaintSelect.setColor(mTextColorSelect); 
    mTextPaintSelect.setAlpha(0); 
  } 
  public void setTextColorNormal(int mTextColorNormal) { 
    this.mTextColorNormal = mTextColorNormal; 
    mTextPaintNormal.setColor(mTextColorNormal); 
    mTextPaintNormal.setAlpha(0xff); 
  } 
  public void setTextValue(String TextValue) { 
    this.mTextValue = TextValue; 
  } 
  public void setIconText(int[] iconSelId,String TextValue) { 
    this.mIconSelect = BitmapFactory.decodeResource(getResources(), iconSelId[0]); 
    this.mIconNormal = BitmapFactory.decodeResource(getResources(), iconSelId[1]); 
    this.mTextValue = TextValue; 
  } 
   
  public void setTabAlpha(float alpha){ 
    int paintAlpha = (int)(alpha*255) ; 
    mIconPaintSelect.setAlpha(paintAlpha); 
    mIconPaintNormal.setAlpha(255-paintAlpha); 
    mTextPaintSelect.setAlpha(paintAlpha); 
    mTextPaintNormal.setAlpha(255-paintAlpha); 
    invalidate(); 
  } 
} 

分析： 以上代码，功能实现 tab 的每个 item 的内容，在微信的项目中也就是，一个图标加一个字体，

关键代码就在public void setTabAlpha(float alpha) 这个方法，此方法是 viewPager 切换 item 时，不断改变偏移量来调用，从而不断改变

每个画笔的透明度，实现图标和颜色的渐变；是不是很简单？到这里其实我们颜色渐变的代码就已经实现了。接下来的内容可以忽略

这样我们只需要在 MainActivity 的 xml 中定义一个线性布局，然后放如四个我们自定义的 View 进去，就可以了。但是这样你就满足了吗？

我先来给你们看看我的MainActivity的代码；

[java] view plain copy
package moon.wechat; 
import android.support.v4.app.Fragment; 
import android.support.v4.app.FragmentManager; 
import android.support.v4.app.FragmentPagerAdapter; 
import android.support.v4.view.ViewPager; 
import android.support.v7.app.ActionBarActivity; 
import android.os.Bundle; 
import java.util.HashMap; 
import java.util.Map; 
import moon.wechat.view.TabView; 
public class MainActivity extends ActionBarActivity { 
  private String[] mTitle = {"微信", "通讯录", "发现", "我"}; 
  private int[] mIconSelect = {R.drawable.al_, R.drawable.al8, R.drawable.alb, R.drawable.ald}; 
  private int[] mIconNormal = {R.drawable.ala, R.drawable.al9, R.drawable.alc, R.drawable.ale}; 
  private ViewPager mViewPager ; 
  private TabView mTabView ; 
  private Map<Integer,Fragment> mFragmentMap ; 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    mFragmentMap = new HashMap<>() ; 
    mViewPager = (ViewPager)findViewById(R.id.id_view_pager) ; 
    mViewPager.setOffscreenPageLimit(4); 
    mViewPager.setAdapter(new PageAdapter(getSupportFragmentManager())); 
    mTabView = (TabView)findViewById(R.id.id_tab) ; 
    mTabView.setViewPager(mViewPager); 
  } 
  private Fragment getFragment(int position){ 
    Fragment fragment = mFragmentMap.get(position) ; 
    if(fragment == null){ 
      switch (position){ 
        case 0: 
          fragment = new WeChatFragment() ; 
          break ; 
        case 1: 
          fragment = new WeContactFragment(); 
          break ; 
        case 2: 
          fragment = new WeDiscoverFragment(); 
          break; 
        case 3: 
          fragment = new GameFragment() ; 
//          fragment = new WeMineFragment(); 
          break; 
      } 
      mFragmentMap.put(position,fragment) ; 
    } 
    return fragment ; 
  } 
  class PageAdapter extends FragmentPagerAdapter implements TabView.OnItemIconTextSelectListener{ 
    public PageAdapter(FragmentManager fm) { 
      super(fm); 
    } 
    @Override 
    public Fragment getItem(int position) { 
      return getFragment(position); 
    } 
    @Override 
    public int[] onIconSelect(int position) { 
      int icon[] = new int[2] ; 
      icon[0] = mIconSelect[position] ; 
      icon[1] = mIconNormal[position] ; 
      return icon; 
    } 
    @Override 
    public String onTextSelect(int position) { 
      return mTitle[position]; 
    } 
    @Override 
    public int getCount() { 
      return mTitle.length; 
    } 
  } 
} 

是不是很简单，而 xml 更简单

[html] view plain copy
<LinearLayout xmlns:android="Http://schemas.android.com/apk/res/android" 
  xmlns:zgy="http://schemas.android.com/apk/res-auto" 
  android:layout_width="match_parent" 
  android:layout_height="match_parent" 
  android:background="@android:color/white" 
  android:orientation="vertical"> 
  <android.support.v4.view.ViewPager 
    android:id="@+id/id_view_pager" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:layout_weight="1" 
    > 
    </android.support.v4.view.ViewPager> 
  <moon.wechat.view.TabView 
    android:id="@+id/id_tab" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:orientation="horizontal" 
    android:background="#eeeeee" 
    zgy:text_size="12sp" 
    zgy:text_normal_color="#ff777777" 
    zgy:text_select_color="#ff45c01a" 
    zgy:item_padding="7dp"> 
   </moon.wechat.view.TabView> 
</LinearLayout> 

可以看到没有定义我们刚刚自定义的 TabItem，而是使用的 TabView，那 TabView 到底是啥东西？相信大家都想到了，TabView 其实就是我们自定义的线性布局，

[java] view plain copy
package moon.wechat.view; 
import android.content.Context; 
import android.content.res.TypedArray; 
import android.support.v4.view.PagerAdapter; 
import android.support.v4.view.ViewPager; 
import android.util.AttributeSet; 
import android.util.Log; 
import android.util.TypedValue; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.LinearLayout; 
import java.util.ArrayList; 
import java.util.List; 
import moon.wechat.R; 
 
public class TabView extends LinearLayout implements View.OnClickListener { 
  private ViewPager mViewPager; 
  private ViewPager.OnPageChangeListener mOnPageChangeListener; 
  private PagerAdapter mPagerAdapter; 
  private int mChildSize; 
  private List<TabItem> mTabItems; 
  private OnItemIconTextSelectListener mListener; 
  private int mTextSize = 12; 
  private int mTextColorSelect = 0xff45c01a; 
  private int mTextColorNormal = 0xff777777; 
  private int mPadding = 10; 
  public TabView(Context context) { 
    this(context, null); 
  } 
  public TabView(Context context, AttributeSet attrs) { 
    this(context, attrs, 0); 
  } 
  public TabView(Context context, AttributeSet attrs, int defStyleAttr) { 
    super(context, attrs, defStyleAttr); 
    TypedArray typedArray = getResources().obtainAttributes(attrs, R.styleable.TabView); 
    int N = typedArray.getIndexCount(); 
    for (int i = 0; i < N; i++) { 
      switch (typedArray.getIndex(i)) { 
        case R.styleable.TabView_text_size: 
          mTextSize = (int) typedArray.getDimension(i, TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, 
              mTextSize, getResources().getDisplayMetrics())); 
          break; 
        case R.styleable.TabView_text_normal_color: 
          mTextColorNormal = typedArray.getColor(i, mTextColorNormal); 
          break; 
        case R.styleable.TabView_text_select_color: 
          mTextColorSelect = typedArray.getColor(i, mTextColorSelect); 
          break; 
        case R.styleable.TabView_item_padding: 
          mPadding = (int) typedArray.getDimension(i, TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 
              mPadding, getResources().getDisplayMetrics())); 
          break; 
      } 
    } 
    typedArray.recycle(); 
    mTabItems = new ArrayList<>(); 
  } 
  public void setViewPager(final ViewPager mViewPager) { 
    if (mViewPager == null) { 
      return; 
    } 
    this.mViewPager = mViewPager; 
    this.mPagerAdapter = mViewPager.getAdapter(); 
    if (this.mPagerAdapter == null) { 
      throw new RuntimeException("亲，在您设置TabView的ViewPager时，请先设置ViewPager的PagerAdapter"); 
    } 
    this.mChildSize = this.mPagerAdapter.getCount(); 
    this.mViewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() { 
      @Override 
      public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { 
//        Log.v("zgy","=============position="+position+",====positionOffset="+positionOffset) ; 
        View leftView; 
        View rightView; 
        if (positionOffset > 0) { 
          leftView = mViewPager.getChildAt(position); 
          rightView = mViewPager.getChildAt(position + 1); 
          leftView.setAlpha(1 - positionOffset); 
          rightView.setAlpha(positionOffset); 
          mTabItems.get(position).setTabAlpha(1 - positionOffset); 
          mTabItems.get(position + 1).setTabAlpha(positionOffset); 
        } else { 
          mViewPager.getChildAt(position).setAlpha(1); 
          mTabItems.get(position).setTabAlpha(1 - positionOffset); 
        } 
        if (mOnPageChangeListener != null) { 
mOnPageChangeListener.onPageScrolled(position, positionOffset, positionOffsetPixels); 
        } 
      } 
      @Override 
      public void onPageSelected(int position) { 
        if (mOnPageChangeListener != null) { 
mOnPageChangeListener.onPageSelected(position); 
        } 
      } 
      @Override 
      public void onPageScrollStateChanged(int state) { 
        if (mOnPageChangeListener != null) { 
mOnPageChangeListener.onPageScrollStateChanged(state); 
        } 
      } 
    }); 
    if (mPagerAdapter instanceof OnItemIconTextSelectListener) { 
      mListener = (OnItemIconTextSelectListener) mPagerAdapter; 
    }else { 
      throw new RuntimeException("请让你的pageAdapter实现OnItemIconTextSelectListener接口"); 
    } 
    initItem(); 
  } 
  public void setOnPageChangeListener(ViewPager.OnPageChangeListener mOnPageChangeListener) { 
    this.mOnPageChangeListener = mOnPageChangeListener; 
  } 
  private void initItem() { 
    for (int i = 0; i < mChildSize; i++) { 
      TabItem tabItem = new TabItem(getContext()); 
      LayoutParams params = new LayoutParams(0, ViewGroup.LayoutParams.WRAP_CONTENT, 1); 
      tabItem.setPadding(mPadding, mPadding, mPadding, mPadding); 
      tabItem.setIconText(mListener.onIconSelect(i), mListener.onTextSelect(i)); 
      tabItem.setTextSize(mTextSize); 
      tabItem.setTextColorNormal(mTextColorNormal); 
      tabItem.setTextColorSelect(mTextColorSelect); 
      tabItem.setLayoutParams(params); 
      tabItem.setTag(i); 
      tabItem.setOnClickListener(this); 
      mTabItems.add(tabItem); 
      addView(tabItem); 
    } 
  } 
  @Override 
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { 
    super.onMeasure(widthMeasureSpec, heightMeasureSpec); 
  } 
  @Override 
  public void onClick(View v) { 
    int position = (Integer) v.getTag(); 
    if (mViewPager.getCurrentItem() == position) { 
      return; 
    } 
    for (TabItem tabItem : mTabItems) { 
      tabItem.setTabAlpha(0); 
    } 
    mTabItems.get(position).setTabAlpha(1); 
    mViewPager.setCurrentItem(position, false); 
  } 
  public interface OnItemIconTextSelectListener { 
    int[] onIconSelect(int position); 
    String onTextSelect(int position); 
  } 
} 

注释有点少，额，不是少，是压根就没有，其实，这个类的代码不需要注释，我相信大家都能看懂，我就讲下他的作用吧，

添加 item 监听 ViewPager 的滚动事件，从而设置相应 item 之间的颜色渐变， 设置相应 ViewPage 的透明度 为 TabItem 设置监听事件，

其实上面很多功能本来是在 MainActivity 中实现的，为了减少 Activity 内部的代码量，抽取出来，到达低耦合，高内聚的效果。

Ok，以上就是 微信6.1 tab 栏颜色渐变效果的实现全过程。

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