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Android应用中仿今日头条App制作ViewPager指示器

时间：2021-11-24 04:14 编辑：来源：阅读：
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摘要：Android应用中仿今日头条App制作ViewPager指示器

[b]一、概述 [/b]顶部ViewPager指示器的字体变色，该效果图是这样的： [img]http://files.jb51.net/file_images/article/201604/2016419161403484.jpg?2016319161425[/img] 大概是今天头条的app，神奇的地方就在于，切换ViewPager页面的时候，顶部指示器改成了字体颜色的变化，个人觉得还是不错的。那么核心的地方就是做一个支持字体这样逐渐染色就可以了，我大概想了32s，扫描了一些可能实现的方案，最终定位了一个靠谱的，下面我就带大家开始实现的征程。实现之前贴一下我们的效果图： [b]1、简单使用 [/b] [img]http://files.jb51.net/file_images/article/201604/2016419161454304.gif?201631916157[/img] 效果如上图了，关于颜失色的改变我添加了两个方向，一个是左方向，一个是有方向。单纯的使用，可能觉得没什么意思，下面看结合ViewPager使用的一个例子。 [b]2、结合ViewPager使用 [/b] [img]http://files.jb51.net/file_images/article/201604/2016419161515807.gif?2016319161527[/img] 可以看到我们切换页面的时候，上面的指示器的效果，棒棒哒~~~ 当然了，学会了原理，你可以扩展，可以做个性的进度条，可以将字体变色改为背景色变色，可以把方向改为上下，太多了，自己去抠脚想把。 [b]二、原理 [/b]看完效果图，有木有什么思路~~~花几分钟想想，因为原理很简单~~ 我大致想了下，目测绘制半个字估计不行，那么就在绘制范围上下功夫，你可以全部绘制，但是我控制显示的范围，所以上述效果：其实是绘制了两遍字体，但是呢，分别控制了绘制的显示范围，实现了逐渐变色的效果，那么对于范围的控制，有什么方便的API么，显然是有的 canvas有个clipRect的方法~~~ok，原理分析完毕~~ [b]三、实现 [/b]说到实现，那第一步肯定又是自定义属性，我们这里的属性，需要text,textSize,textOriginColor,textChangeColor,progress，大致看一下，应该都能看出来作用吧，看不出来没事，结合下面的代码。tip:我们的View叫做ColorTrackView，感谢小七的命名。 [b]1、自定义属性和获取 [/b]attr.xml

<?xml version="1.0" encoding="utf-8"?> 
<resources> 
 
 <attr name="text" format="string" /> 
 <attr name="text_size" format="dimension" /> 
 <attr name="text_origin_color" format="color|reference" /> 
 <attr name="text_change_color" format="color|reference" /> 
 <attr name="progress" format="float" /> 
 <attr name="direction"> 
  <enum name="left" value="0" /> 
  <enum name="right" value="1" /> 
 </attr> 
 
 <declare-styleable name="ColorTrackView"> 
  <attr name="text" /> 
  <attr name="text_size" /> 
  <attr name="text_origin_color" /> 
  <attr name="text_change_color" /> 
  <attr name="progress" /> 
  <attr name="direction" /> 
 </declare-styleable> 
 
</resources>

然后在我们的ColorTrackView的构造方法中进行获取这些个渣渣属性：

public class ColorTrackView extends View 
{ 
 
 private int mTextStartX; 
  
 public enum Direction 
 { 
  LEFT , RIGHT ; 
 } 
 
 private int mDirection = DIRECTION_LEFT; 
  
 private static final int DIRECTION_LEFT = 0 ; 
 private static final int DIRECTION_RIGHT= 1 ; 
  
 public void setDirection(int direction) 
 { 
  mDirection = direction; 
 } 
  
 private String mText = "张鸿洋"; 
 private Paint mPaint; 
 private int mTextSize = sp2px(30); 
 
 private int mTextOriginColor = 0xff000000; 
 private int mTextChangeColor = 0xffff0000; 
 
 private Rect mTextBound = new Rect(); 
 private int mTextWidth; 
 
 private int mRealWidth; 
 
 private float mProgress; 
 
 public ColorTrackView(Context context) 
 { 
  super(context, null); 
 } 
 
 public ColorTrackView(Context context, AttributeSet attrs) 
 { 
  super(context, attrs); 
 
  mPaint = new Paint(Paint.ANTI_ALIAS_FLAG); 
 
  TypedArray ta = context.obtainStyledAttributes(attrs, 
    R.styleable.ColorTrackView); 
  mText = ta.getString(R.styleable.ColorTrackView_text); 
  mTextSize = ta.getDimensionPixelSize( 
    R.styleable.ColorTrackView_text_size, mTextSize); 
  mTextOriginColor = ta.getColor( 
    R.styleable.ColorTrackView_text_origin_color, 
    mTextOriginColor); 
  mTextChangeColor = ta.getColor( 
    R.styleable.ColorTrackView_text_change_color, 
    mTextChangeColor); 
  mProgress = ta.getFloat(R.styleable.ColorTrackView_progress, 0); 
   
  mDirection = ta.getInt(R.styleable.ColorTrackView_direction, mDirection); 
   
  ta.recycle(); 
 
  mPaint.setTextSize(mTextSize); 
  measureText(); 
 
 } 

private void measureText() 
 { 
  mTextWidth = (int) mPaint.measureText(mText); 
  mPaint.getTextBounds(mText, 0, mText.length(), mTextBound); 
 }

可以看到我同时贴出了成员变量，大家简单看下就行了，都比较简单。获取了属性，初始化完成一些成员变量以后，那么应该走向我们的measure之旅了~~ [b]2、onMeasure[/b]

@Override 
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) 
 { 
  int width = measureWidth(widthMeasureSpec); 
  int height = measureHeight(heightMeasureSpec); 
  setMeasuredDimension(width, height); 
 
  mRealWidth = getMeasuredWidth() - getPaddingLeft() - getPaddingRight(); 
  mTextStartX = mRealWidth / 2 - mTextWidth / 2; 
 
 } 
 
 private int measureHeight(int measureSpec) 
 { 
  int mode = MeasureSpec.getMode(measureSpec); 
  int val = MeasureSpec.getSize(measureSpec); 
  int result = 0; 
  switch (mode) 
  { 
  case MeasureSpec.EXACTLY: 
   result = val; 
   break; 
  case MeasureSpec.AT_MOST: 
  case MeasureSpec.UNSPECIFIED: 
   result = mTextBound.height(); 
   break; 
  } 
  result = mode == MeasureSpec.AT_MOST ? Math.min(result, val) : result; 
  return result + getPaddingTop() + getPaddingBottom(); 
 } 
 
 private int measureWidth(int measureSpec) 
 { 
  int mode = MeasureSpec.getMode(measureSpec); 
  int val = MeasureSpec.getSize(measureSpec); 
  int result = 0; 
  switch (mode) 
  { 
  case MeasureSpec.EXACTLY: 
   result = val; 
   break; 
  case MeasureSpec.AT_MOST: 
  case MeasureSpec.UNSPECIFIED: 
   // result = mTextBound.width(); 
   result = mTextWidth; 
   break; 
  } 
  result = mode == MeasureSpec.AT_MOST ? Math.min(result, val) : result; 
  return result + getPaddingLeft() + getPaddingRight(); 
 }

关于测量，也是比较传统的写法，根据传入的widthMeasureSpec、heightMeasureSpec，利用MeasureSpec分别获取模式和值，如何是EXACTLY万事大吉，如果是AT_MOST、UNSPECIFIED那么就进行自己测量需要的空间，当然了，最好注意如果是AT_MOST不应该大于父类传入的值。这里提一下，如果偷懒的话，可以选择继承TextView，然后测量就不需要写了，TextView默认帮你实现了，还能利用TextView的一些属性，不过咱们这个例子比较简单，我最终还是选择了继承View，继承View有种everything under control 的感觉。测量完成以后，不用说都是绘制了。 [b]3、onDraw[/b]

@Override 
 protected void onDraw(Canvas canvas) 
 { 
  super.onDraw(canvas); 
  int r = (int) (mProgress* mTextWidth +mTextStartX ); 
   
  if(mDirection == DIRECTION_LEFT) 
  { 
   drawChangeLeft(canvas, r); 
   drawOriginLeft(canvas, r); 
  }else 
  { 
    drawOriginRight(canvas, r); 
    drawChangeRight(canvas, r); 
  } 
 
 } 
  
 private void drawChangeRight(Canvas canvas, int r) 
 { 
  drawText(canvas, mTextChangeColor, (int) (mTextStartX +(1-mProgress)*mTextWidth), mTextStartX+mTextWidth ); 
 } 
 private void drawOriginRight(Canvas canvas, int r) 
 { 
  drawText(canvas, mTextOriginColor, mTextStartX, (int) (mTextStartX +(1-mProgress)*mTextWidth) ); 
 } 
 
 private void drawChangeLeft(Canvas canvas, int r) 
 { 
  drawText(canvas, mTextChangeColor, mTextStartX, (int) (mTextStartX + mProgress * mTextWidth) ); 
 } 
 
 private void drawOriginLeft(Canvas canvas, int r) 
 { 
  drawText(canvas, mTextOriginColor, (int) (mTextStartX + mProgress * mTextWidth), mTextStartX +mTextWidth ); 
 } 
  
 private void drawText(Canvas canvas , int color , int startX , int endX) 
 { 
  mPaint.setColor(color); 
  canvas.save(Canvas.CLIP_SAVE_FLAG); 
  canvas.clipRect(startX, 0, endX, getMeasuredHeight()); 
  canvas.drawText(mText, mTextStartX, getMeasuredHeight() / 2 
    + mTextBound.height() / 2, mPaint); 
  canvas.restore(); 
 }

绘制的核心就在于利用mProgress和方向去计算应该clip的范围，具体的参考代码，没什么难点。有了范围以后，无非就是drawText~~~这里只讲主要代码。主要的方法介绍完毕，我们就该测试了。 [b]四、测试[/b] [b]1、简单测试 [/b]布局文件

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
 xmlns:tools="http://schemas.android.com/tools" 
 xmlns:zhy="http://schemas.android.com/apk/res-auto" 
 android:layout_width="match_parent" 
 android:layout_height="match_parent" > 
 
 <com.zhy.view.ColorTrackView 
  android:id="@+id/id_changeTextColorView" 
  android:layout_width="match_parent" 
  android:layout_height="wrap_content" 
  android:layout_centerInParent="true" 
  android:background="#44ff0000" 
  android:padding="10dp" 
  zhy:progress="0" 
  zhy:text="张鸿洋" 
  zhy:text_change_color="#ffff0000" 
  zhy:text_origin_color="#ff000000" 
  zhy:text_size="60sp" /> 
 
 <LinearLayout 
  android:layout_width="match_parent" 
  android:layout_height="wrap_content" 
  android:layout_alignParentBottom="true" 
  android:gravity="center" 
  android:orientation="horizontal" > 
 
  <Button 
   android:id="@+id/id_left" 
   android:layout_width="wrap_content" 
   android:layout_height="wrap_content" 
   android:onClick="startLeftChange" 
   android:text="StartLeft" /> 
 
  <Button 
   android:layout_width="wrap_content" 
   android:layout_height="wrap_content" 
   android:layout_toRightOf="@id/id_left" 
   android:onClick="startRightChange" 
   android:text="StartRight" /> 
 </LinearLayout> 
 
</RelativeLayout>

注意我们的自定义属性的命名空间，该布局就一个ColorTrackView，然后两个按钮来控制进度。 SimpleUseActivity:

package com.zhy.viewpagerIndicator; 
 
import android.animation.ObjectAnimator; 
import android.annotation.SuppressLint; 
import android.app.Activity; 
import android.os.Bundle; 
import android.view.View; 
 
import com.zhy.view.ColorTrackView; 
 
public class SimpleUseActivity extends Activity 
{ 
 
 ColorTrackView mView; 
 
 @Override 
 protected void onCreate(Bundle savedInstanceState) 
 { 
  super.onCreate(savedInstanceState); 
  setContentView(R.layout.activity_simple_main); 
  mView = (ColorTrackView) findViewById(R.id.id_changeTextColorView); 
   
 
 } 
 
 @SuppressLint("NewApi") 
 public void startLeftChange(View view) 
 { 
  mView.setDirection(0); 
  ObjectAnimator.ofFloat(mView, "progress", 0, 1).setDuration(2000) 
    .start(); 
 } 
 
 @SuppressLint("NewApi") 
 public void startRightChange(View view) 
 { 
  mView.setDirection(1); 
  ObjectAnimator.ofFloat(mView, "progress", 0, 1).setDuration(2000) 
    .start(); 
 } 
 
}

这里拿属性动画进行的测试，没有导入3.0以下兼容包，有需要自己导入。效果图就是上面张鸿洋那张。 [b]2、结合ViewPager [/b]布局文件：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
 xmlns:zhy="http://schemas.android.com/apk/res-auto" 
 xmlns:tools="http://schemas.android.com/tools" 
 android:layout_width="match_parent" 
 android:layout_height="match_parent" 
 android:orientation="vertical" > 
 
 <LinearLayout 
  android:layout_width="match_parent" 
  android:layout_height="50dp" 
  android:orientation="horizontal" > 
 
  <com.zhy.view.ColorTrackView 
   android:id="@+id/id_tab_01" 
   android:layout_width="0dp" 
   android:layout_height="match_parent" 
   android:layout_weight="1" 
   zhy:progress="1" 
   zhy:text="简介" 
   zhy:text_change_color="#ffff0000" 
   zhy:text_origin_color="#ff000000" 
   zhy:text_size="18sp" /> 
 
  <com.zhy.view.ColorTrackView 
   android:id="@+id/id_tab_02" 
   android:layout_width="0dp" 
   android:layout_height="match_parent" 
   android:layout_weight="1" 
   zhy:text="评价" 
   zhy:text_change_color="#ffff0000" 
   zhy:text_origin_color="#ff000000" 
   zhy:text_size="18sp" /> 
 
  <com.zhy.view.ColorTrackView 
   android:id="@+id/id_tab_03" 
   android:layout_width="0dp" 
   android:layout_height="match_parent" 
   android:layout_weight="1" 
   zhy:text="相关" 
   zhy:text_change_color="#ffff0000" 
   zhy:text_origin_color="#ff000000" 
   zhy:text_size="18sp" /> 
 
   
 </LinearLayout> 
 
 <android.support.v4.view.ViewPager 
  android:id="@+id/id_viewpager" 
  android:layout_width="match_parent" 
  android:layout_height="0dp" 
  android:layout_weight="1" > 
 </android.support.v4.view.ViewPager> 
 
</LinearLayout>

3个ColorTrackView代表Tab,下面是ViewPager ViewPagerUseActivity:

package com.zhy.viewpagerIndicator; 
 
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.FragmentPagerAdapter; 
import android.support.v4.view.ViewPager; 
import android.support.v4.view.ViewPager.OnPageChangeListener; 
import android.util.Log; 
 
import com.zhy.view.ColorTrackView; 
 
public class ViewPagerUseActivity extends FragmentActivity 
{ 
 private String[] mTitles = new String[] { "简介", "评价", "相关" }; 
 private ViewPager mViewPager; 
 private FragmentPagerAdapter mAdapter; 
 private TabFragment[] mFragments = new TabFragment[mTitles.length]; 
 private List<ColorTrackView> mTabs = new ArrayList<ColorTrackView>(); 
 
 @Override 
 protected void onCreate(Bundle savedInstanceState) 
 { 
  super.onCreate(savedInstanceState); 
  setContentView(R.layout.activity_vp_main); 
 
  initViews(); 
  initDatas(); 
  initEvents(); 
 } 
 
 private void initEvents() 
 { 
  mViewPager.setOnPageChangeListener(new OnPageChangeListener() 
  { 
   @Override 
   public void onPageSelected(int position) 
   { 
   } 
 
   @Override 
   public void onPageScrolled(int position, float positionOffset, 
     int positionOffsetPixels) 
   { 
    if (positionOffset > 0) 
    { 
     ColorTrackView left = mTabs.get(position); 
     ColorTrackView right = mTabs.get(position + 1); 
      
     left.setDirection(1); 
     right.setDirection(0); 
     Log.e("TAG", positionOffset+""); 
     left.setProgress( 1-positionOffset); 
     right.setProgress(positionOffset); 
    } 
   } 
 
   @Override 
   public void onPageScrollStateChanged(int state) 
   { 
 
   } 
  }); 
 
 } 
 
 private void initDatas() 
 { 
 
  for (int i = 0; i < mTitles.length; i++) 
  { 
   mFragments[i] = (TabFragment) TabFragment.newInstance(mTitles[i]); 
  } 
 
  mAdapter = new FragmentPagerAdapter(getSupportFragmentManager()) 
  { 
   @Override 
   public int getCount() 
   { 
    return mTitles.length; 
   } 
 
   @Override 
   public Fragment getItem(int position) 
   { 
    return mFragments[position]; 
   } 
 
  }; 
 
  mViewPager.setAdapter(mAdapter); 
  mViewPager.setCurrentItem(0); 
 } 
 
 private void initViews() 
 { 
  mViewPager = (ViewPager) findViewById(R.id.id_viewpager); 
   
  mTabs.add((ColorTrackView) findViewById(R.id.id_tab_01)); 
  mTabs.add((ColorTrackView) findViewById(R.id.id_tab_02)); 
  mTabs.add((ColorTrackView) findViewById(R.id.id_tab_03)); 
 } 
 
}

TabFragment

package com.zhy.viewpagerIndicator; 
 
import java.util.Random; 
 
import android.graphics.Color; 
import android.os.Bundle; 
import android.support.v4.app.Fragment; 
import android.view.Gravity; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.TextView; 
 
public class TabFragment extends Fragment 
{ 
 public static final String TITLE = "title"; 
 private String mTitle = "Defaut Value"; 
 
 @Override 
 public void onCreate(Bundle savedInstanceState) 
 { 
  super.onCreate(savedInstanceState); 
  if (getArguments() != null) 
  { 
   mTitle = getArguments().getString(TITLE); 
  } 
 } 
 
 @Override 
 public View onCreateView(LayoutInflater inflater, ViewGroup container, 
   Bundle savedInstanceState) 
 { 
  TextView tv = new TextView(getActivity()); 
  tv.setTextSize(60); 
  Random r = new Random(); 
  tv.setBackgroundColor(Color.argb(r.nextInt(120), r.nextInt(255), 
    r.nextInt(255), r.nextInt(255))); 
  tv.setText(mTitle); 
  tv.setGravity(Gravity.CENTER); 
  return tv; 
 
 } 
 
 public static TabFragment newInstance(String title) 
 { 
  TabFragment tabFragment = new TabFragment(); 
  Bundle bundle = new Bundle(); 
  bundle.putString(TITLE, title); 
  tabFragment.setArguments(bundle); 
  return tabFragment; 
 } 
 
}

效果图就是上面“结合ViewPager使用”的那张。

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