Android ImageView繪制圓角效果

前言

Android 開發中，我們經常需要實現圖片的圓形/圓角的效果，我們可以使用兩種方式來實現這樣的效果。一種是使用Xfermode，另一種是BitmapShader來實現。下面我將分別介紹這兩種用法。

使用Xfermode的方式實現
使用該方式的關鍵代碼，如下：

  private Bitmap creataBitmap(Bitmap bitmap) {

    //用指定的一個Bitmap來構建一個畫布
    Bitmap target = Bitmap.createBitmap(1000,1000, Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(target);
    final Paint paint = new Paint();
    paint.setColor(Color.GREEN);
    paint.setAntiAlias(true);
    //在剛才的畫布上繪制一個圓形區域
    canvas.drawCircle(500,500,500,paint);
    //設置Xfermode，使用SRC_IN模式,這樣可以取到第二張圖片重疊後的區域
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    //在畫布上繪制第二個需要顯示的bitmap
    canvas.drawBitmap(bitmap,0,0,paint);
    return target;
  }

上面代碼中看出在指定的畫布上繪制了兩層圖像，一個是半徑為500像素的圓形，一個是將目標Bitmap繪制在上面。之間還調用了paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));作用是這兩個繪制的效果圖疊加後，取得第二個圖的交集圖。所以，我們先繪制一個圓形，然後繪制Bitmap，交集為圓形，取出的就是圓形區域的Bitmap了。
PorterDuff.Mode中一共有16種效果顯示，如下：

可以根據不同的Mode，控制顯示的效果圖。

開始應用

1.自定義屬性在attrs.xml中

<?xml version="1.0" encoding="utf-8"?>
<resources>

  <attr name="borderRadius" format="dimension" />
  <attr name="type">
    <enum name="circle" value="0"/>
    <enum name="round" value="1"/>
  </attr>
  <attr name="src" format="reference"/>
  <declare-styleable name="RoundImageView">
    <attr name="borderRadius"/>
    <attr name="type"/>
    <attr name="src"/>
  </declare-styleable>

</resources>

2.自定義View

public class RoundImageView extends View {

  private int type;
  private static final int TYPE_CIRCLE = 0;
  private static final int TYPE_ROUND = 1;
  //圖片
  private Bitmap mSrc;
  //圓角大小
  private int mRadius;
  //高度
  private int mWidth;
  //寬度
  private int mHeight;

  public RoundImageView(Context context, AttributeSet attrs) {
    super(context, attrs);
    //獲取自定義的屬性
    TypedArray a = context.obtainStyledAttributes(attrs,R.styleable.RoundImageView);
    //獲取自定以屬性的數目
    int count = a.getIndexCount();
    for (int i=0 ; i<count ; i++){
      int attr = a.getIndex(i);
      switch (attr){
        case R.styleable.RoundImageView_borderRadius:
          int defValue = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,10f,getResources().getDisplayMetrics());
          mRadius = a.getDimensionPixelSize(attr, defValue);
          break;
        case R.styleable.RoundImageView_type:
          type = a.getInt(attr,0);
          break;
        case R.styleable.RoundImageView_src:
          mSrc = BitmapFactory.decodeResource(getResources(),a.getResourceId(attr,0));
          break;
      }
    }

    a.recycle();
  }

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    //設置寬度
    int specMode = MeasureSpec.getMode(widthMeasureSpec);
    int specSize = MeasureSpec.getSize(widthMeasureSpec);
    if (specMode == MeasureSpec.EXACTLY){
      mWidth = specSize;
    }else {
      int desireByImg = getPaddingLeft() + getPaddingRight() + mSrc.getWidth();
      if (specMode == MeasureSpec.AT_MOST)// wrap_content
      {
        mWidth = Math.min(desireByImg, specSize);
      } else
        mWidth = desireByImg;
    }

    //設置高度
    specMode = MeasureSpec.getMode(heightMeasureSpec);
    specSize = MeasureSpec.getSize(heightMeasureSpec);
    if (specMode == MeasureSpec.EXACTLY){
      mHeight = specSize;
    }else {
      int desire = getPaddingTop() + getPaddingBottom() + mSrc.getHeight();
      if (specMode == MeasureSpec.AT_MOST)// wrap_content
      {
        mHeight = Math.min(desire, specSize);
      } else
        mHeight = desire;
    }

    setMeasuredDimension(mWidth,mHeight);
  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    switch (type){
      case TYPE_CIRCLE:
        int min = Math.min(mWidth,mHeight);
        //從當前存在的Bitmap，按一定的比例創建一個新的Bitmap。
        mSrc = Bitmap.createScaledBitmap(mSrc, min, min, false);
        canvas.drawBitmap(createCircleImage(mSrc, min), 0, 0, null);

        break;
      case TYPE_ROUND:
        mSrc = Bitmap.createScaledBitmap(mSrc, mWidth, mHeight, false);
        canvas.drawBitmap(createRoundConerImage(mSrc), 0, 0, null);

        break;
    }
  }

  /**
   * 繪制圓角
   * @param source
   * @return
   */
  private Bitmap createRoundConerImage(Bitmap source) {
    final Paint paint = new Paint();
    paint.setAntiAlias(true);
    Bitmap target = Bitmap.createBitmap(mWidth, mHeight, Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(target);
    RectF rect = new RectF(0, 0, mWidth, mHeight);
    canvas.drawRoundRect(rect, mRadius, mRadius, paint);
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    canvas.drawBitmap(source, 0, 0, paint);
    return target;
  }

  /**
   * 繪制圓形
   * @param source
   * @param min
   * @return
   */
  private Bitmap createCircleImage(Bitmap source, int min) {
    final Paint paint = new Paint();
    paint.setAntiAlias(true);
    Bitmap target = Bitmap.createBitmap(min, min, Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(target);
    canvas.drawCircle(min/2,min/2,min/2,paint);
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    canvas.drawBitmap(source, 0, 0, paint);
    return target;
  }
}

3.布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
       xmlns:roundview="http://schemas.android.com/apk/res-auto"
       xmlns:tools="http://schemas.android.com/tools"
       android:id="@+id/activity_main"
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       android:orientation="vertical"
       android:padding="10dp"
       tools:context="mo.yumf.com.myviews.MainActivity">


  <mo.yumf.com.myviews.RoundImageView
    android:layout_width="200dp"
    android:layout_height="200dp"
    android:layout_marginTop="20dp"
    roundview:borderRadius="10dp"
    roundview:src="@drawable/ac_default_icon"
    roundview:type="round"/>

  <mo.yumf.com.myviews.RoundImageView
    android:layout_width="200dp"
    android:layout_height="200dp"
    android:layout_marginTop="20dp"
    roundview:src="@drawable/ac_default_icon"
    roundview:type="circle"/>
</LinearLayout>

上面的自定義View中，存在一個局限，那就是只能在布局中設置要加載的圖片資源，不能在代碼中設置圖片。下面我們使用同樣的方式，選擇自定義ImageView來實現。

public class RoundImageView extends ImageView {

  private int type;
  private static final int TYPE_CIRCLE = 0;
  private static final int TYPE_ROUND = 1;
  //圖片
  private Bitmap mSrc;
  //圓角大小
  private int mRadius;

  public RoundImageView(Context context, AttributeSet attrs) {
    super(context, attrs);
    //獲取自定義的屬性
    TypedArray a = context.obtainStyledAttributes(attrs,R.styleable.RoundImageView);
    //獲取自定以屬性的數目
    int count = a.getIndexCount();
    for (int i=0 ; i<count ; i++){
      int attr = a.getIndex(i);
      switch (attr){
        case R.styleable.RoundImageView_borderRadius:
          int defValue = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,10f,getResources().getDisplayMetrics());
          mRadius = a.getDimensionPixelSize(attr, defValue);
          break;
        case R.styleable.RoundImageView_type:
          type = a.getInt(attr,0);
          break;
      }
    }

    a.recycle();
  }

  @Override
  protected void onDraw(Canvas canvas) {
    if (getDrawable() != null){
      Bitmap bitmap = getBitmap(getDrawable());
      if (bitmap != null){
        switch (type){
          case TYPE_CIRCLE:
            //獲取ImageView中的寬高，取最小值
            int min = Math.min(getMeasuredWidth(),getMeasuredHeight());
            //從當前存在的Bitmap，按一定的比例創建一個新的Bitmap。
            mSrc = Bitmap.createScaledBitmap(bitmap, min, min, false);
            canvas.drawBitmap(createCircleImage(mSrc, min), 0, 0, null);

            break;
          case TYPE_ROUND:
            mSrc = Bitmap.createScaledBitmap(bitmap, getMeasuredWidth(), getMeasuredHeight(), false);
            canvas.drawBitmap(createRoundConerImage(mSrc), 0, 0, null);

            break;
        }
      }
    }else {

      super.onDraw(canvas);
    }
  }

  private Bitmap getBitmap(Drawable drawable) {
    if (drawable instanceof BitmapDrawable){
      return ((BitmapDrawable)drawable).getBitmap();
    }else if (drawable instanceof ColorDrawable){
      Rect rect = drawable.getBounds();
      int width = rect.right - rect.left;
      int height = rect.bottom - rect.top;
      int color = ((ColorDrawable)drawable).getColor();
      Bitmap bitmap = Bitmap.createBitmap(width,height, Bitmap.Config.ARGB_8888);
      Canvas canvas = new Canvas(bitmap);
      canvas.drawARGB(Color.alpha(color),Color.red(color), Color.green(color), Color.blue(color));
      return bitmap;
    }else {
      return null;
    }
  }


  /**
   * 繪制圓角
   * @param source
   * @return
   */
  private Bitmap createRoundConerImage(Bitmap source) {
    final Paint paint = new Paint();
    paint.setAntiAlias(true);
    Bitmap target = Bitmap.createBitmap(getMeasuredWidth(), getMeasuredHeight(), Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(target);
    RectF rect = new RectF(0, 0, getMeasuredWidth(), getMeasuredHeight());
    canvas.drawRoundRect(rect, mRadius, mRadius, paint);
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    canvas.drawBitmap(source, 0, 0, paint);
    return target;
  }

  /**
   * 繪制圓形
   * @param source
   * @param min
   * @return
   */
  private Bitmap createCircleImage(Bitmap source, int min) {
    final Paint paint = new Paint();
    paint.setAntiAlias(true);
    Bitmap target = Bitmap.createBitmap(min, min, Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(target);
    canvas.drawCircle(min/2,min/2,min/2,paint);
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    canvas.drawBitmap(source, 0, 0, paint);
    return target;
  }
}

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