3.2学习内容:android图片灰度化，VelocityTracker类

以你之姓@ 2022-08-07 03:39 107阅读 0赞

今日项目出现一个bug：

出现代码：

int width, height;
    				height = bmSrc.getHeight();
    				width = bmSrc.getWidth();
    
    				bmpGray = Bitmap.createBitmap(width, height,
    						Bitmap.Config.RGB_565);// android4.4.2(SM-N9008V),NativeMethod
    				Canvas c = new Canvas(bmpGray);
    				Paint paint = new Paint();
    				ColorMatrix cm = new ColorMatrix();
    				cm.setSaturation(0);
    				ColorMatrixColorFilter f = new ColorMatrixColorFilter(cm);
    				paint.setColorFilter(f);
    				c.drawBitmap(bmSrc, 0, 0, paint);

原因：android sm-n9008v中系统没有这个创建图片的类,包nativmethod方法,网上很流行以上的灰度化方法，其实是有错的！

bmpGray = Bitmap.createBitmap(width, height,
    						Bitmap.Config.RGB_565);// android4.4.2(SM-N9008V),NativeMethod

解决方案：

使用另外一种灰度化方法：

// constant factors
    	          final double GS_RED = 0.299;
    	          final double GS_GREEN = 0.587;
    	          final double GS_BLUE = 0.114;
    	          
    	          // create output bitmap
    	          Bitmap bmOut = Bitmap.createBitmap(bmSrc.getWidth(), bmSrc.getHeight(), bmSrc.getConfig());
    	          // pixel information
    	          int A, R, G, B;
    	          int pixel;
    	          
    	          // get image size
    	          int width = bmSrc.getWidth();
    	          int height = bmSrc.getHeight();
    	          
    	          // scan through every single pixel
    	          for(int x = 0; x < width; ++x) {
    	           for(int y = 0; y < height; ++y) {
    	            // get one pixel color
    	            pixel = bmSrc.getPixel(x, y);
    	            // retrieve color of all channels
    	            A = Color.alpha(pixel);
    	            R = Color.red(pixel);
    	            G = Color.green(pixel);
    	            B = Color.blue(pixel);
    	            // take conversion up to one single value
    	            R = G = B = (int)(GS_RED * R + GS_GREEN * G + GS_BLUE * B);
    	            // set new pixel color to output bitmap
    	            bmOut.setPixel(x, y, Color.argb(A, R, G, B));
    	           }
    	          }
    	          
    	          // return final image
    	          return bmOut;

来源：http://zhidao.baidu.com/link?url=qKdqviboKNQdRW2e\_1NCJKyDArCd3fqgpthYWUpZd9RxKuWJ\_Qdn66wvACJ-gHvdtws7AqWfMnZqtlo96-lLPCfWNeqNGgL0y6pXejrBKPe

安卓复选框对话框：

Builder builder=new android.app.AlertDialog.Builder(this);  
//设置对话框的图标  
builder.setIcon(R.drawable.header);  
//设置对话框的标题  
builder.setTitle("复选框对话框");  
builder.setMultiChoiceItems(R.array.hobby, flags, new DialogInterface.OnMultiChoiceClickL

android.view.VelocityTracker主要用跟踪触摸屏事件（flinging事件和其他gestures手势事件）的速率。用addMovement(MotionEvent)函数将Motion event加入到VelocityTracker类实例中.你可以使用getXVelocity() 或getXVelocity()获得横向和竖向的速率到速率时，但是使用它们之前请先调用computeCurrentVelocity(int)来初始化速率的单位 。

private VelocityTracker mVelocityTracker;//生命变量

//在onTouchEvent(MotionEvent ev)中

if (mVelocityTracker == null) \{

mVelocityTracker = VelocityTracker. obtain () ;//获得VelocityTracker类实例

mVelocityTracker. addMovement (ev); //将事件加入到VelocityTracker类实例中

//判断当ev事件是MotionEvent.ACTION\_UP时：计算速率

final VelocityTracker velocityTracker = mVelocityTracker;

// 1000 provides pixels per second

velocityTracker.computeCurrentVelocity(1, (float)0.01) ;  //设置maxVelocity值为0.1时，速率大于0.01时，显示的速率都是0.01,速率小于0.01时，显示正常

Log.i("test","velocityTraker"+velocityTracker.getXVelocity());

velocityTracker.computeCurrentVelocity(1000);  //设置units的值为1000，意思为一秒时间内运动了多少个像素

Log.i("test","velocityTraker"+velocityTracker.getXVelocity());