Android开发使用自定义View将圆角矩形绘制在Canvas上的方法

 /**
   * Call this to create a new shader that will draw with a bitmap.
   *
   * @param bitmap      The bitmap to use inside the shader
   * @param tileX       The tiling mode for x to draw the bitmap in.
   * @param tileY       The tiling mode for y to draw the bitmap in.
   */
  public BitmapShader(Bitmap bitmap, TileMode tileX, TileMode tileY) {
......
}

package com.example.test;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapShader;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.RectF;
import android.graphics.Shader;
import android.util.AttributeSet;
import android.view.View;
public class RounderCornerImageView extends View {
  private Bitmap mImage;// source bitmap
  private Paint mBitmapPaint;//paint
  private RectF mBrounds;//rect
  private float mRadius=20.0f;//round
  public RounderCornerImageView(Context context) {
    this(context, null);
  }
  public RounderCornerImageView(Context context, AttributeSet attrs) {
    this(context, attrs, 0);
  }
  public RounderCornerImageView(Context context, AttributeSet attrs,
      int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    init();
  }
  private void init() {
    mBitmapPaint=new Paint(Paint.ANTI_ALIAS_FLAG);
    mBrounds=new RectF();
  }
  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    // TODO Auto-generated method stub
    int height,width;
    height=width=0;
    //obtain bitmap size
    int imageHeight,imageWidth;
    if (null!=mImage) {
      imageHeight=imageWidth=0;
    }else
    {
      imageHeight=mImage.getHeight();
      imageWidth=mImage.getWidth();
    }
    //obtain best measure data and set on View
    width=getMeasurement(widthMeasureSpec,imageWidth);
    height=getMeasurement(heightMeasureSpec, imageHeight);
    //set View last size
    setMeasuredDimension(width, height);
  }
  /**
   * measure width and height by specMode
   **/
  private int getMeasurement(int measureSpec, int contentSize) {
    int specSize=MeasureSpec.getSize(measureSpec);
    switch (MeasureSpec.getMode(measureSpec)) {
    case MeasureSpec.AT_MOST:
      return Math.min(specSize, contentSize);
    case MeasureSpec.UNSPECIFIED:
      return contentSize;
    case MeasureSpec.EXACTLY:
      return specSize;
    default:
      return 0;
    }//switch
  }
  @Override
  protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    if (w!=oldw || h!=oldh) {
      int imageWidth,imageHeight;
      if (null==mImage) {
        imageWidth=imageHeight=0;
      }else
      {
        imageWidth=mImage.getWidth();
        imageHeight=mImage.getHeight();
      }
      //center point
      int left=(w-imageWidth)/2;
      int top=(h-imageHeight)/2;
      mBrounds.set(left, top, left+imageWidth, top+imageHeight);
      if (null!=mBitmapPaint.getShader()) {
        Matrix m=new Matrix();
        m.setTranslate(left, top);
        mBitmapPaint.getShader().setLocalMatrix(m);
      }
    }
  }
  public void setImage(Bitmap bitmap) {
    if (mImage!=bitmap) {
      mImage=bitmap;
      if (null!=mImage) {
        BitmapShader shader=new BitmapShader(bitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
        mBitmapPaint.setShader(shader);
      }else {
        mBitmapPaint.setShader(null);
      }
      requestLayout();//invalidated the layout of this view by onDraw()
    }
  }
  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    if (null!=mBitmapPaint) {
      //draw Round Rect
      canvas.drawRoundRect(mBrounds, mRadius, mRadius, mBitmapPaint);
    }
  }
}

package com.example.test;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
public class RoundActivity extends Activity{
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    RounderCornerImageView view=new RounderCornerImageView(this);
    Bitmap souBitmap=BitmapFactory.decodeResource(getResources(), R.drawable.sun);
    view.setImage(souBitmap);
    setContentView(view);
  }
}