Android ImageView分析并展开

对于它的使用。除了注意ScaleType的理解和设置外，还须要注意其它一些问题，比方设置一张大的背景图片内存占用和释放等。

还有它的拓展性方面，像圆角图片、圆形图片、图片边框等等。因此，假设想熟练使用这个控件，就须要对事实上现的机制有一个基本的了解。

假设设置了drawableResource。那么Drawable就是其值；假设没有。那么就从ContentResolver获取一个Drawable。

 private void resolveUri() {
        if (mDrawable != null) {
            return;
        }

        Resources rsrc = getResources();
        if (rsrc == null) {
            return;
        }

        Drawable d = null;

        if (mResource != 0) {
            try {
                d = rsrc.getDrawable(mResource);
            } catch (Exception e) {
                Log.w("ImageView", "Unable to find resource: " + mResource, e);
                // Don‘t try again.
                mUri = null;
            }
        } else if (mUri != null) {
            String scheme = mUri.getScheme();
            if (ContentResolver.SCHEME_ANDROID_RESOURCE.equals(scheme)) {
                try {
                    // Load drawable through Resources, to get the source density information
                    ContentResolver.OpenResourceIdResult r =
                            mContext.getContentResolver().getResourceId(mUri);
                    d = r.r.getDrawable(r.id);
                } catch (Exception e) {
                    Log.w("ImageView", "Unable to open content: " + mUri, e);
                }
            } else if (ContentResolver.SCHEME_CONTENT.equals(scheme)
                    || ContentResolver.SCHEME_FILE.equals(scheme)) {
                InputStream stream = null;
                try {
                    stream = mContext.getContentResolver().openInputStream(mUri);
                    d = Drawable.createFromStream(stream, null);
                } catch (Exception e) {
                    Log.w("ImageView", "Unable to open content: " + mUri, e);
                } finally {
                    if (stream != null) {
                        try {
                            stream.close();
                        } catch (IOException e) {
                            Log.w("ImageView", "Unable to close content: " + mUri, e);
                        }
                    }
                }
        } else {
                d = Drawable.createFromPath(mUri.toString());
            }
   
            if (d == null) {
                System.out.println("resolveUri failed on bad bitmap uri: " + mUri);
                // Don‘t try again.
                mUri = null;
            }
        } else {
            return;
        }

        updateDrawable(d);
    }

 private void updateDrawable(Drawable d) {
        if (mDrawable != null) {
            mDrawable.setCallback(null);
            unscheduleDrawable(mDrawable);
        }
        mDrawable = d;
        if (d != null) {
            d.setCallback(this);
            if (d.isStateful()) {
                d.setState(getDrawableState());
            }
            d.setLevel(mLevel);
            d.setLayoutDirection(getLayoutDirection());
            d.setVisible(getVisibility() == VISIBLE, true);
            mDrawableWidth = d.getIntrinsicWidth();
            mDrawableHeight = d.getIntrinsicHeight();
            applyColorMod();
            configureBounds();
        } else {
            mDrawableWidth = mDrawableHeight = -1;
        }
    }

if (mAdjustViewBounds) {
                resizeWidth = widthSpecMode != MeasureSpec.EXACTLY;
                resizeHeight = heightSpecMode != MeasureSpec.EXACTLY;
               
                desiredAspect = (float) w / (float) h;
            }

 w += pleft + pright;
            h += ptop + pbottom;
            w = Math.max(w, getSuggestedMinimumWidth());
            h = Math.max(h, getSuggestedMinimumHeight());
            widthSize = resolveSizeAndState(w, widthMeasureSpec, 0);
            heightSize = resolveSizeAndState(h, heightMeasureSpec, 0);
        }
        setMeasuredDimension(widthSize, heightSize);

  @Override
 protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        if (mDrawable == null) {
            return; // couldn‘t resolve the URI
        }

        if (mDrawableWidth == 0 || mDrawableHeight == 0) {
            return;     // nothing to draw (empty bounds)
        }

        if (mDrawMatrix == null && mPaddingTop == 0 && mPaddingLeft == 0) {
            mDrawable.draw(canvas);
        } else {
            int saveCount = canvas.getSaveCount();
            canvas.save();
           
            if (mCropToPadding) {
                final int scrollX = mScrollX;
                final int scrollY = mScrollY;
                canvas.clipRect(scrollX + mPaddingLeft, scrollY + mPaddingTop,
                        scrollX + mRight - mLeft - mPaddingRight,
                        scrollY + mBottom - mTop - mPaddingBottom);
            }
           
            canvas.translate(mPaddingLeft, mPaddingTop);

            if (mDrawMatrix != null) {
                canvas.concat(mDrawMatrix);
            }
            mDrawable.draw(canvas);
            canvas.restoreToCount(saveCount);
        }
    }

private void configureBounds() {
        if (mDrawable == null || !mHaveFrame) {
            return;
        }

        int dwidth = mDrawableWidth;
        int dheight = mDrawableHeight;

        int vwidth = getWidth() - mPaddingLeft - mPaddingRight;
        int vheight = getHeight() - mPaddingTop - mPaddingBottom;

        boolean fits = (dwidth < 0 || vwidth == dwidth) &&
                       (dheight < 0 || vheight == dheight);

        if (dwidth <= 0 || dheight <= 0 || ScaleType.FIT_XY == mScaleType) {
            /* If the drawable has no intrinsic size, or we‘re told to
                scaletofit, then we just fill our entire view.
            */
            mDrawable.setBounds(0, 0, vwidth, vheight);
            mDrawMatrix = null;
        } else {
            // We need to do the scaling ourself, so have the drawable
            // use its native size.
            mDrawable.setBounds(0, 0, dwidth, dheight);

            if (ScaleType.MATRIX == mScaleType) {
                // Use the specified matrix as-is.
                if (mMatrix.isIdentity()) {
                    mDrawMatrix = null;
                } else {
                    mDrawMatrix = mMatrix;
                }
            } else if (fits) {
                // The bitmap fits exactly, no transform needed.
                mDrawMatrix = null;
            } else if (ScaleType.CENTER == mScaleType) {
                // Center bitmap in view, no scaling.
                mDrawMatrix = mMatrix;
                mDrawMatrix.setTranslate((int) ((vwidth - dwidth) * 0.5f + 0.5f),
                                         (int) ((vheight - dheight) * 0.5f + 0.5f));
            } else if (ScaleType.CENTER_CROP == mScaleType) {
                mDrawMatrix = mMatrix;

                float scale;
                float dx = 0, dy = 0;

                if (dwidth * vheight > vwidth * dheight) {
                    scale = (float) vheight / (float) dheight;
                    dx = (vwidth - dwidth * scale) * 0.5f;
                } else {
                    scale = (float) vwidth / (float) dwidth;
                    dy = (vheight - dheight * scale) * 0.5f;
                }

                mDrawMatrix.setScale(scale, scale);
                mDrawMatrix.postTranslate((int) (dx + 0.5f), (int) (dy + 0.5f));
            } else if (ScaleType.CENTER_INSIDE == mScaleType) {
                mDrawMatrix = mMatrix;
                float scale;
                float dx;
                float dy;
               
                if (dwidth <= vwidth && dheight <= vheight) {
                    scale = 1.0f;
                } else {
                    scale = Math.min((float) vwidth / (float) dwidth,
                            (float) vheight / (float) dheight);
                }
               
                dx = (int) ((vwidth - dwidth * scale) * 0.5f + 0.5f);
                dy = (int) ((vheight - dheight * scale) * 0.5f + 0.5f);

                mDrawMatrix.setScale(scale, scale);
                mDrawMatrix.postTranslate(dx, dy);
            } else {
                // Generate the required transform.
                mTempSrc.set(0, 0, dwidth, dheight);
                mTempDst.set(0, 0, vwidth, vheight);
               
                mDrawMatrix = mMatrix;
                mDrawMatrix.setRectToRect(mTempSrc, mTempDst, scaleTypeToScaleToFit(mScaleType));
            }
        }
    }

  InputStream is = this.getResources().openRawResource(R.drawable.xx); 
     BitmapFactory.Options options=new BitmapFactory.Options(); 
     options.inJustDecodeBounds = false; 
     options.inSampleSize = 10;   //width。hight设为原来的十分一 
     Bitmap btp =BitmapFactory.decodeStream(is,null,options); 

  public static Bitmap readBitMap(Context context, int resId){  
     BitmapFactory.Options opt = new BitmapFactory.Options();  
         opt.inPreferredConfig = Bitmap.Config.RGB_565;   
       opt.inPurgeable = true;  
       opt.inInputShareable = true;   
      InputStream is = context.getResources().openRawResource(resId);  
        return BitmapFactory.decodeStream(is,null,opt);  
      }

   if(!bmp.isRecycle() ){ 
         bmp.recycle()   //回收图片所占的内存 
         system.gc()  //提醒系统及时回收 
     } 

  private final static float TARGET_HEAP_UTILIZATION = 0.75f; 

 VMRuntime.getRuntime().setTargetHeapUtilization(TARGET_HEAP_UTILIZATION);

private final static int CWJ_HEAP_SIZE = 6* 1024* 1024 ;
VMRuntime.getRuntime().setMinimumHeapSize(CWJ_HEAP_SIZE); //设置最小heap内存为6MB大小。