折腾了一天,今天基本把自定义扫描二维码界面实现了,主要碰到的问题是文本过长,要居中并换行,绘制图片,点击切换不同图片,打开或关闭闪关灯,结果发现在一些机型上出现空指针异常,又牵扯到硬件加速问题。。。参考了网上一下解决办法,记录一下
先上一张效果图
开发者遇到的问题以及知识点
1.长文本换行与居中
处理文字可以使用StaticLayout,本例中用到的构造方法是
public StaticLayout(CharSequence source, TextPaint paint,
int width,
Alignment align, float spacingmult, float spacingadd,
boolean includepad)
1).需要填写的字符串
2) .画笔
3).layout的宽度,字符串超出宽度时,自动换行。
4).对齐方式,有ALIGN_CENTER, ALIGN_NORMAL, ALIGN_OPPOSITE 三种。使用ALIGN_CENTER可居中
5).相对行间距,相对字体大小,1.5f表示行间距为1.5倍的字体高度。
6).相对行间距,0表示0个像素。
实际行间距等于这两者的和。
7).没查到这个参数表示的意思
默认是从画布的(0,0)坐标开始,如果需要在指定位置绘画,在draw之前移Canvas的起始坐标canvas.translate(x,y);
在canvas.translate(x,y)操作中,可以使用canvas的一些方法进行处理
canvas.save();//锁画布(为了保存之前的画布状态)
canvas.translate(x, y);//把当前画布的原点移到(x,y),后面的操作都以(x,y)作为参照点,默认原点为(0,0)
canvas.restore();//把当前画布返回(调整)到上一个save()状态之前
如果不进行处理也可以,再重新绘制其他View的时候,坐标就需要相应的调整了
2.第二个问题是在界面上绘制图片
绘制图片有两种方法
1)、基本
drawBitmap(Bitmap bitmap, float left, float top, Paint paint)
//Bitmap:图片,left:图片左边位置,top:图片顶部的位置
2)、对图片裁剪以及限定显示区域
drawBitmap(Bitmap bitmap, Rect src, RectF dst, Paint paint);
bitmap的默认坐标是0,0.矩形src为我们所剪辑的图片的包围框,即你所剪的图片,为空,就是整张图片。
矩形dst容纳裁剪的图片,然后根据此矩形的位置设置图片的位置。此参数不能为空。
当你剪的图片大小大于dst时,多余的部分将不会显示。
也就是说src是裁减区,对原始图的裁减区域,而dst是代表图片显示位置.
3.drawBitmap()方法空指针异常
在小米手机上测试,竟然提示
java.lang.NullPointerException
at android.view.GLES20RecordingCanvas.drawBitmap
在网上查了一下,这个是和硬件加速有关系,在AndroidManifest.xml application下设定:
android:hardwareAccelerated=”false”
测试没发现问题
下边记录一下在网上找到的关于硬件加速的资料
硬件加速可以在一下四个级别开启或关闭:
Application
Activity
Window
View
Application级别
往您的应用程序AndroidManifest.xml文件为application标签添加application android:hardwareAccelerated=”true”属性即可为整个应用程序开启硬件加速
Activity级别
控制每个activity是否开启硬件加速,只需在activity元素中添加android:hardwareAccelerated属性
Window级别
使用如下代码开启某个window的硬件加速:
getWindow().setFlags( WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED, WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED);
View级别
用以下的代码关闭单个view的硬件加速:
myView.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
在这四个层次中,应用和Activity是可以选择的,Window只能打开,View只能关闭。
检查是否开启硬件加速
/ 方法一
// 返回true,如果myView挂在一个开启了硬件加速的Window之下
myView.isHardwareAccelerated();
// 方法二
// 返回true,如果canvas在绘制的时候启用了硬件加速
// 尽量采用此方法来判断是否开启了硬件加速
canvas.isHardwareAccelerated();
4.zxing二维码扫描开启或关闭闪光灯
不要忘记在onDestroy方法里关闭闪光灯
public void enableFlash(){
FlashlightManager.enableFlashlight(); try { if (context.getPackageManager().hasSystemFeature( PackageManager.FEATURE_CAMERA_FLASH)) { Parameters p = camera.getParameters(); p.setFlashMode(Parameters.FLASH_MODE_TORCH); camera.setParameters(p); } } catch (Exception e) { e.printStackTrace(); } } public void disableFlash(){ FlashlightManager.enableFlashlight(); try { if (context.getPackageManager().hasSystemFeature( PackageManager.FEATURE_CAMERA_FLASH)) { Parameters p = camera.getParameters(); p.setFlashMode(Parameters.FLASH_MODE_OFF); camera.setParameters(p); } } catch (Exception e) { e.printStackTrace(); } }
5.点击canvas绘制的图片
思路:在onTouchEvent中获取手指点击坐标,判断坐标是否在图片范围之内,如果在,进行点击操作
@Override
public boolean onTouchEvent(MotionEvent event) { // 获取点击屏幕时的点的坐标 float x = event.getX(); float y = event.getY(); if((x>drawableLeft&&x<drawableRight) ||(y>drawableTop&&y<drawableBottom)){ if(isOpen){ CameraManager.get().enableFlash(); }else{ CameraManager.get().disableFlash(); } drawBitMap(isOpen); isOpen=!isOpen; } return super.onTouchEvent(event); }
上完整代码
public final class ViewfinderView extends View { private static final String TAG = "log"; /** * 刷新界面的时间 */ private static final long ANIMATION_DELAY = 10L; private static final int OPAQUE = 0xFF; /** * 四个绿色边角对应的长度 */ private int ScreenRate; /** * 四个绿色边角对应的宽度 */ private static final int CORNER_WIDTH = 10; /** * 扫描框中的中间线的宽度 */ private static final int MIDDLE_LINE_WIDTH = 6; /** * 扫描框中的中间线的与扫描框左右的间隙 */ private static final int MIDDLE_LINE_PADDING = 5; /** * 中间那条线每次刷新移动的距离 */ private static final int SPEEN_DISTANCE = 5; /** * 手机的屏幕密度 */ private static float density; /** * 字体大小 */ private static final int TEXT_SIZE = 16; /** * 字体距离扫描框下边的距离 */ private static final int TEXT_PADDING_BOTTOM = 50; /** * 字体距离扫描框上边的距离 */ private static final int TEXT_PADDING_TOP = 50; /** * 画笔对象的引用 */ private Paint paint; /** * 中间滑动线的最顶端位置 */ private int slideTop; /** * 中间滑动线的最底端位置 */ private int slideBottom; private Bitmap resultBitmap; private final int maskColor; private final int resultColor; private final int resultPointColor; private Collection<ResultPoint> possibleResultPoints; private Collection<ResultPoint> lastPossibleResultPoints; boolean isFirst; StaticLayout layoutTop;//绘制扫描框上边字体 StaticLayout layoutBottom;//绘制扫描框下字体 TextPaint textPaint;//绘制字体 //绘制显示的开灯关灯图片 private Resources mResources; private Paint mBitPaint; private Bitmap mBitmap; private Rect mSrcRect, mDestRect; private Rect frame; private Canvas drawBitmapCanvas;//绘制图片 //绘制图片的上下左右坐标 private int drawableLeft; private int drawableTop; private int drawableBottom; private int drawableRight; //是否点击开灯图片 private boolean isOpen=false; //是否绘画图片 private boolean isDraw = false; public ViewfinderView(Context context, AttributeSet attrs) { super(context, attrs); density = context.getResources().getDisplayMetrics().density; //将像素转换成dp ScreenRate = (int) (20 * density); paint = new Paint(); Resources resources = getResources(); maskColor = resources.getColor(R.color.viewfinder_mask); resultColor = resources.getColor(R.color.result_view); resultPointColor = resources.getColor(R.color.possible_result_points); possibleResultPoints = new HashSet<ResultPoint>(5); } @Override public void onDraw(Canvas canvas) { //中间的扫描框 frame = CameraManager.get().getFramingRect(); if (frame == null) { return; } drawBitmapCanvas = canvas; //初始化中间线滑动的最上边和最下边 if (!isFirst) { isFirst = true; slideTop = frame.top; slideBottom = frame.bottom; } //获取屏幕的宽和高 int width = canvas.getWidth(); int height = canvas.getHeight(); paint.setColor(resultBitmap != null ? resultColor : maskColor); //画出扫描框外面的阴影部分,共四个部分,扫描框的上面到屏幕上面,扫描框的下面到屏幕下面 //扫描框的左边面到屏幕左边,扫描框的右边到屏幕右边 canvas.drawRect(0, 0, width, frame.top, paint); canvas.drawRect(0, frame.top, frame.left, frame.bottom + 1, paint); canvas.drawRect(frame.right + 1, frame.top, width, frame.bottom + 1, paint); canvas.drawRect(0, frame.bottom + 1, width, height, paint); if (resultBitmap != null) { // Draw the opaque result bitmap over the scanning rectangle paint.setAlpha(OPAQUE); canvas.drawBitmap(resultBitmap, frame.left, frame.top, paint); } else { //画扫描框边上的角,总共8个部分 paint.setColor(Color.GREEN); canvas.drawRect(frame.left, frame.top, frame.left + ScreenRate, frame.top + CORNER_WIDTH, paint); canvas.drawRect(frame.left, frame.top, frame.left + CORNER_WIDTH, frame.top + ScreenRate, paint); canvas.drawRect(frame.right - ScreenRate, frame.top, frame.right, frame.top + CORNER_WIDTH, paint); canvas.drawRect(frame.right - CORNER_WIDTH, frame.top, frame.right, frame.top + ScreenRate, paint); canvas.drawRect(frame.left, frame.bottom - CORNER_WIDTH, frame.left + ScreenRate, frame.bottom, paint); canvas.drawRect(frame.left, frame.bottom - ScreenRate, frame.left + CORNER_WIDTH, frame.bottom, paint); canvas.drawRect(frame.right - ScreenRate, frame.bottom - CORNER_WIDTH, frame.right, frame.bottom, paint); canvas.drawRect(frame.right - CORNER_WIDTH, frame.bottom - ScreenRate, frame.right, frame.bottom, paint); //绘制中间的线,每次刷新界面,中间的线往下移动SPEEN_DISTANCE slideTop += SPEEN_DISTANCE; if (slideTop >= frame.bottom) { slideTop = frame.top; } canvas.drawRect(frame.left + MIDDLE_LINE_PADDING, slideTop - MIDDLE_LINE_WIDTH / 2, frame.right - MIDDLE_LINE_PADDING, slideTop + MIDDLE_LINE_WIDTH / 2, paint); /* Rect lineRect = new Rect(); lineRect.left = frame.left; lineRect.right = frame.right; lineRect.top = slideTop; lineRect.bottom = slideTop + 18; canvas.drawBitmap(((BitmapDrawable)(getResources().getDrawable(R.drawable.qrline))).getBitmap(), null, lineRect, paint); */ //画扫描框上面的字,并且居中 if (textPaint == null) { textPaint = new TextPaint(); } textPaint.setColor(Color.WHITE); textPaint.setTextSize(TEXT_SIZE * density); //textPaint.setAlpha(0x40); textPaint.setTypeface(Typeface.DEFAULT_BOLD); String textTop = "XXXXXXXXXXXXXXXXXXXXX"; // float textWidthTop = paint.measureText(textTop); if (layoutTop == null) { layoutTop = new StaticLayout(textTop, textPaint, frame.right - frame.left, Layout.Alignment.ALIGN_CENTER, 1.0F, 0.0F, true); } canvas.save();//锁画布(为了保存之前的画布状态) //开始绘制的位置 //把当前画布的原点移到(frame.left, (float) (frame.top - (float) TEXT_PADDING_TOP * density)), // 后面的操作都以(frame.left, (float) (frame.top - (float) TEXT_PADDING_TOP * density))作为参照点,默认原点为(0,0) canvas.translate(frame.left, (float) (frame.top - (float) TEXT_PADDING_TOP * density)); layoutTop.draw(canvas); canvas.restore();//把当前画布返回(调整)到上一个save()状态之前 //画扫描框下面的字,并且居中 String textBottom = "XXXXXXXXXXXXXXXXXXXXXXXXXX"; // float textWidthTop = paint.measureText(textTop); if (layoutBottom == null) { layoutBottom = new StaticLayout(textBottom, textPaint, frame.right - frame.left, Layout.Alignment.ALIGN_CENTER, 1.0F, 0.0F, true); } canvas.save();//锁画布(为了保存之前的画布状态) //开始绘制的位置 canvas.translate(frame.left, (float) (frame.bottom) + 18); layoutBottom.draw(canvas); canvas.restore(); Collection<ResultPoint> currentPossible = possibleResultPoints; Collection<ResultPoint> currentLast = lastPossibleResultPoints; if (currentPossible.isEmpty()) { lastPossibleResultPoints = null; } else { possibleResultPoints = new HashSet<ResultPoint>(5); lastPossibleResultPoints = currentPossible; paint.setAlpha(OPAQUE); paint.setColor(resultPointColor); for (ResultPoint point : currentPossible) { canvas.drawCircle(frame.left + point.getX(), frame.top + point.getY(), 6.0f, paint); } } if (currentLast != null) { paint.setAlpha(OPAQUE / 2); paint.setColor(resultPointColor); for (ResultPoint point : currentLast) { canvas.drawCircle(frame.left + point.getX(), frame.top + point.getY(), 3.0f, paint); } } //只刷新扫描框的内容,其他地方不刷新 postInvalidateDelayed(ANIMATION_DELAY, frame.left, frame.top, frame.right, frame.bottom); drawBitMap(isOpen); } } @Override public boolean onTouchEvent(MotionEvent event) { // 获取点击屏幕时的点的坐标 float x = event.getX(); float y = event.getY(); if((x>drawableLeft&&x<drawableRight) ||(y>drawableTop&&y<drawableBottom)){ if(!isOpen){ CameraManager.get().enableFlash(); }else{ CameraManager.get().disableFlash(); } drawBitMap(isOpen); isOpen=!isOpen; } return super.onTouchEvent(event); } //绘制图片,并且根据点击切换不同的图标,切换是否开灯图标 public void drawBitMap(boolean isOpen){ //绘制显示的图片 mResources = getResources(); if(mBitPaint==null){ mBitPaint = new Paint(Paint.ANTI_ALIAS_FLAG); } mBitPaint.setFilterBitmap(true); mBitPaint.setDither(true); try { if(isOpen){ mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.defaultalarm);; }else{ mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.alarm); } }catch (Exception e){ e.printStackTrace(); } //要绘制的bitmap 区域 if(mSrcRect == null){ mSrcRect = new Rect(0, 0, mBitmap.getWidth(), mBitmap.getHeight()); } //要将bitmap 绘制在屏幕的什么地方 // 计算左边位置