大家好,又见面了,我是全栈君,今天给大家准备了Idea注册码。
2014.6.12
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。
ImageView也是直接继承于View类。基本的结构图例如以下:
public ImageView(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); initImageView(); TypedArray a = context.obtainStyledAttributes(attrs, com.android.internal.R.styleable.ImageView, defStyle, 0); Drawable d = a.getDrawable(com.android.internal.R.styleable.ImageView_src); if (d != null) { setImageDrawable(d); } mBaselineAlignBottom = a.getBoolean( com.android.internal.R.styleable.ImageView_baselineAlignBottom, false); mBaseline = a.getDimensionPixelSize( com.android.internal.R.styleable.ImageView_baseline, -1); setAdjustViewBounds( a.getBoolean(com.android.internal.R.styleable.ImageView_adjustViewBounds, false)); setMaxWidth(a.getDimensionPixelSize( com.android.internal.R.styleable.ImageView_maxWidth, Integer.MAX_VALUE)); setMaxHeight(a.getDimensionPixelSize( com.android.internal.R.styleable.ImageView_maxHeight, Integer.MAX_VALUE)); int index = a.getInt(com.android.internal.R.styleable.ImageView_scaleType, -1); if (index >= 0) { setScaleType(sScaleTypeArray[index]); } int tint = a.getInt(com.android.internal.R.styleable.ImageView_tint, 0); if (tint != 0) { setColorFilter(tint); } int alpha = a.getInt(com.android.internal.R.styleable.ImageView_drawableAlpha, 255); if (alpha != 255) { setAlpha(alpha); } mCropToPadding = a.getBoolean( com.android.internal.R.styleable.ImageView_cropToPadding, false); a.recycle(); //need inflate syntax/reader for matrix } private void initImageView() { mMatrix = new Matrix(); mScaleType = ScaleType.FIT_CENTER; mAdjustViewBoundsCompat = mContext.getApplicationInfo().targetSdkVersion <= Build.VERSION_CODES.JELLY_BEAN_MR1; }
是FIT_CENTER。说到
ScaleType。它是一个枚举类型,用于设置。寻常使用的ScaleType就是在这里定义的。
/** * Options for scaling the bounds of an image to the bounds of this view. */ public enum ScaleType { /** * Scale using the image matrix when drawing. The image matrix can be set using * {@link ImageView#setImageMatrix(Matrix)}. From XML, use this syntax: * <code>android:scaleType="matrix"</code>. */ MATRIX (0), /** * Scale the image using {@link Matrix.ScaleToFit#FILL}. * From XML, use this syntax: <code>android:scaleType="fitXY"</code>. */ FIT_XY (1), /** * Scale the image using {@link Matrix.ScaleToFit#START}. * From XML, use this syntax: <code>android:scaleType="fitStart"</code>. */ FIT_START (2), /** * Scale the image using {@link Matrix.ScaleToFit#CENTER}. * From XML, use this syntax: * <code>android:scaleType="fitCenter"</code>. */ FIT_CENTER (3), /** * Scale the image using {@link Matrix.ScaleToFit#END}. * From XML, use this syntax: <code>android:scaleType="fitEnd"</code>. */ FIT_END (4), /** * Center the image in the view, but perform no scaling. * From XML, use this syntax: <code>android:scaleType="center"</code>. */ CENTER (5), /** * Scale the image uniformly (maintain the image's aspect ratio) so * that both dimensions (width and height) of the image will be equal * to or larger than the corresponding dimension of the view * (minus padding). The image is then centered in the view. * From XML, use this syntax: <code>android:scaleType="centerCrop"</code>. */ CENTER_CROP (6), /** * Scale the image uniformly (maintain the image's aspect ratio) so * that both dimensions (width and height) of the image will be equal * to or less than the corresponding dimension of the view * (minus padding). The image is then centered in the view. * From XML, use this syntax: <code>android:scaleType="centerInside"</code>. */ CENTER_INSIDE (7); ScaleType(int ni) { nativeInt = ni; } final int nativeInt; }
接着就是onMeasure()方法了,它用于设置ImageView的大小。我们在xml文件里设置ImageView的时候,假设指定了固定的宽高,那么onMeasur()方法中測量的大小就是固定的宽高大小;假设是包裹内容,那么就须要进一步的计算。
@Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { resolveUri();//获取图片Drawable int w; int h; // Desired aspect ratio of the view's contents (not including padding) float desiredAspect = 0.0f; // We are allowed to change the view's width boolean resizeWidth = false; // We are allowed to change the view's height boolean resizeHeight = false; final int widthSpecMode = MeasureSpec.getMode(widthMeasureSpec); final int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec); if (mDrawable == null) { // If no drawable, its intrinsic size is 0. mDrawableWidth = -1; mDrawableHeight = -1; w = h = 0; } else { w = mDrawableWidth;在updateDrawable(Drawable d)方法赋值的。 h = mDrawableHeight; if (w <= 0) w = 1; if (h <= 0) h = 1; // We are supposed to adjust view bounds to match the aspect // ratio of our drawable. See if that is possible. if (mAdjustViewBounds) { resizeWidth = widthSpecMode != MeasureSpec.EXACTLY; resizeHeight = heightSpecMode != MeasureSpec.EXACTLY; desiredAspect = (float) w / (float) h; } } int pleft = mPaddingLeft; int pright = mPaddingRight; int ptop = mPaddingTop; int pbottom = mPaddingBottom; int widthSize; int heightSize; if (resizeWidth || resizeHeight) { /* If we get here, it means we want to resize to match the drawables aspect ratio, and we have the freedom to change at least one dimension. */ // Get the max possible width given our constraints widthSize = resolveAdjustedSize(w + pleft + pright, mMaxWidth, widthMeasureSpec); // Get the max possible height given our constraints heightSize = resolveAdjustedSize(h + ptop + pbottom, mMaxHeight, heightMeasureSpec); if (desiredAspect != 0.0f) { // See what our actual aspect ratio is float actualAspect = (float)(widthSize - pleft - pright) / (heightSize - ptop - pbottom); if (Math.abs(actualAspect - desiredAspect) > 0.0000001) { boolean done = false; // Try adjusting width to be proportional to height if (resizeWidth) { int newWidth = (int)(desiredAspect * (heightSize - ptop - pbottom)) + pleft + pright; // Allow the width to outgrow its original estimate if height is fixed. if (!resizeHeight && !mAdjustViewBoundsCompat) { widthSize = resolveAdjustedSize(newWidth, mMaxWidth, widthMeasureSpec); } if (newWidth <= widthSize) { widthSize = newWidth; done = true; } } // Try adjusting height to be proportional to width if (!done && resizeHeight) { int newHeight = (int)((widthSize - pleft - pright) / desiredAspect) + ptop + pbottom; // Allow the height to outgrow its original estimate if width is fixed. if (!resizeWidth && !mAdjustViewBoundsCompat) { heightSize = resolveAdjustedSize(newHeight, mMaxHeight, heightMeasureSpec); } if (newHeight <= heightSize) { heightSize = newHeight; } } } } } else { /* We are either don't want to preserve the drawables aspect ratio, or we are not allowed to change view dimensions. Just measure in the normal way. */ 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); }
在onMeasure方法中,首先调用了resolveUri()这种方法。目的就是为了确定Drawable。
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; } }
那这种方法是做什么用的呢?设置View的最大高度,单独使用无效,须要与setAdjustViewBounds一起使用。假设想设置图片固定大小,又想保持图片宽高比,须要例如以下设置:
1) 设置setAdjustViewBounds为true;
2) 设置maxWidth、MaxHeight;
3) 设置设置layout_width和layout_height为wrap_content。
if (mAdjustViewBounds) { resizeWidth = widthSpecMode != MeasureSpec.EXACTLY; resizeHeight = heightSpecMode != MeasureSpec.EXACTLY; desiredAspect = (float) w / (float) h; }
然后接下来的推断也是基于 resizeWidth和resizeHeight 的值,假设不为true的情况下,会运行例如以下代码:
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); } }
这个是在configureBounds()方法中设置的,
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)); } } }
可是这样直接使用会有一个隐形的弊端,假设显示的图片过多或者单张显示的图片像素过大,就easy出现OOM问题。因此就应该依据需求对图片进行预处理,经常用法有下面几种:
关于图片压缩有非常多方法,这里仅仅是列举一个简单的样例,实际使用价值不大。如有需求能够自行參考其它资料。
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);
因此,改用先通过BitmapFactory.decodeStream方法,创建出一个bitmap。再将其设为ImageView的 source,decodeStream最大的秘密在于其直接调用JNI>>nativeDecodeAsset()来完毕decode。无需再使用java层的createBitmap,从而节省了java层的空间。
假设在读取时加上图片的Config參数,能够跟有效降低载入的内存。从而跟有效阻止抛out of Memory异常。
另外,须要特别注意:decodeStream是直接读取图片资料的字节码了, 不会依据机器的各种分辨率来自己主动适应。使用了decodeStream之后。须要在hdpi和mdpi,ldpi中配置对应的图片资源,否则在不同分辨率机器上都是相同大小(像素点数量)。显示出来的大小就不正确了。
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;
在程序onCreate时就能够调用
VMRuntime.getRuntime().setTargetHeapUtilization(TARGET_HEAP_UTILIZATION);
Android为每一个程序分配的内存能够通过Runtime类的 totalMemory() 、freeMemory() 两个方法获取VM的一些内存信息。
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。
CircleButton为例,这是github上一个项目,实现一个圆形有点击效果的按钮。例如以下:
最后在按下的时候启动一个属性动画,将圆环放大显示,关于具体的分析能够看android-circlebutton介绍 这篇文章。
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