采用Bitmap的extractAlpha产生图片边缘光晕效果
前几天使用一款android手机测试的时候，
发现了应用的 shortcut 九宫格页面有一个点击效果，
就是当点击一个应用的icon图标的时候，会在icon的周围有荧光效果，
无论icon的形状是什么样子的都会有这样的效果,然后又想到Apidemo里面有个alphaDrawable例子
大家可以去在回顾一下，之后我就想到了会不会是使用这个extractAlpha实现的，自己就动手写了个例子
发现效果确实不错，分享给大家
主要关键点
1、设置imageview的src drawable
2、从src drawable中抽取 bitmap的alpha（只有透明度没有颜色）
3、使用bitmap的alpha填充一种颜色后生产新的bitmap
4、使用新生成的bitmap做一个statelistdrawable作为imageview的backgroud
5、这需要注意的是要跟imageview设置几个像素的padding这样才不会让src和backgroud重合
主要的代码：
/* * Copyright (C) 2009 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package com.study;import android.content.Context;import android.content.res.TypedArray;import android.graphics.Bitmap;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.graphics.Bitmap.Config;import android.graphics.drawable.BitmapDrawable;import android.graphics.drawable.StateListDrawable;import android.util.AttributeSet;import android.view.View;import android.view.ViewGroup;import android.widget.ImageView;/** * A layout that arranges its children in a grid. The size of the * cells is set by the {@link #setCellSize} method and the * android:cell_width and android:cell_height attributes in XML. * The number of rows and columns is determined at runtime. Each * cell contains exactly one view, and they flow in the natural * child order (the order in which they were added, or the index * in {@link #addViewAt}. Views can not span multiple cells. */public class FixedGridLayout extends ViewGroup { int mCellWidth; int mCellHeight; public FixedGridLayout(Context context) { super(context); } public FixedGridLayout(Context context, AttributeSet attrs) { super(context, attrs); // Read the resource attributes. TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.FixedGridLayout); mCellWidth = a.getDimensionPixelSize(R.styleable.FixedGridLayout_cellWidth, -1); mCellHeight = a.getDimensionPixelSize(R.styleable.FixedGridLayout_cellHeight, -1); a.recycle(); } public void setCellWidth(int px) { mCellWidth = px; requestLayout(); } public void setCellHeight(int px) { mCellHeight = px; requestLayout(); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { int cellWidthSpec = MeasureSpec.makeMeasureSpec(mCellWidth, MeasureSpec.AT_MOST); int cellHeightSpec = MeasureSpec.makeMeasureSpec(mCellHeight, MeasureSpec.AT_MOST); int count = getChildCount(); for (int index=0; index<count; index++) { final View child = getChildAt(index); child.measure(cellWidthSpec, cellHeightSpec); } // Use the size our parents gave us setMeasuredDimension(resolveSize(mCellWidth*count, widthMeasureSpec), resolveSize(mCellHeight*count, heightMeasureSpec)); } @Override protected void onLayout(boolean changed, int l, int t, int r, int b) { int cellWidth = mCellWidth; int cellHeight = mCellHeight; int columns = (r - l) / cellWidth; if (columns < 0) { columns = 1; } int x = 0; int y = 0; int i = 0; int count = getChildCount(); for (int index=0; index<count; index++) { final View child = getChildAt(index); int w = child.getMeasuredWidth(); int h = child.getMeasuredHeight(); int left = x + ((cellWidth-w)/2); int top = y + ((cellHeight-h)/2); child.layout(left, top, left+w, top+h); if (i >= (columns-1)) { // advance to next row i = 0; x = 0; y += cellHeight; } else { i++; x += cellWidth; } } } @Override protected void onFinishInflate() { super.onFinishInflate(); int cnt = getChildCount(); Paint p = new Paint(); p.setColor(Color.CYAN); for (int i=0; i<cnt; i++) { View v = getChildAt(i); setStateDrawable((ImageView)v, p); } }private void setStateDrawable(ImageView v, Paint p) {BitmapDrawable bd = (BitmapDrawable) v.getDrawable();Bitmap b = bd.getBitmap();Bitmap bitmap = Bitmap.createBitmap(bd.getIntrinsicWidth(), bd.getIntrinsicHeight(), Config.ARGB_8888);Canvas canvas = new Canvas(bitmap);canvas.drawBitmap(b.extractAlpha(), 0, 0, p);StateListDrawable sld = new StateListDrawable();sld.addState(new int[]{android.R.attr.state_pressed}, new BitmapDrawable(bitmap));v.setBackgroundDrawable(sld);}}