android zxing自定义界面，点击按钮开关闪光灯

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 =8;
    /** * 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 = 14;
    /** * 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 = 70;

    /** * 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) (TEXT_SIZE * 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，你要修改扫描框的大小，去CameraManager里面修改
        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-10, 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 = "请将充电桩表面或者液晶屏幕上的二维码放入框内即可自动扫描";
            // float textWidthTop = paint.measureText(textTop);
            if (layoutTop == null) {
                layoutTop = new StaticLayout(textTop, textPaint, frame.right - frame.left-(int)(20* density), 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+(int)(10* density), (float) (frame.top) - (int)( 50 * 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 = "成功扫码后可以为相应车位解开地锁或者开启充电设备";
            // float textWidthTop = paint.measureText(textTop);
            if (layoutBottom == null) {
                layoutBottom = new StaticLayout(textBottom, textPaint, frame.right - frame.left-(int)(20* density), 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,相对偏移
            canvas.translate(frame.left+(int)(10* density), (float) (frame.bottom) + (int)(10* density));
            layoutBottom.draw(canvas);
            canvas.restore();


            Collection<ResultPoint> currentPossible = possibleResultPoints;
            Collection<ResultPoint> currentLast = lastPossibleResultPoints;
            if (currentPossible.isEmpty()) {
                lastPossibleResultPoints = null;
            } else {
                possibleResultPoints = new HashSet<>(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);

        //要绘制的bitmap 区域
        try {
            if(isOpen){
                mBitmap =  BitmapFactory.decodeResource(getResources(), R.mipmap.openlight);
            }else{
                mBitmap =  BitmapFactory.decodeResource(getResources(), R.mipmap.closelight);

            }

        }catch (Exception e){
            e.printStackTrace();
        }
        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
        int left =frame.left+(frame.right-frame.left)/2- mBitmap.getWidth() / 2;
        // 计算上边位置
        int top = frame.bottom +  (int)(50 * density)+(int)(20* density);

        drawableLeft = left;
        drawableRight = left+mBitmap.getWidth();
        drawableTop = top;
        drawableBottom = top+mBitmap.getHeight();


        if(mDestRect == null){
            mDestRect = new Rect(drawableLeft,drawableTop, drawableRight,drawableBottom);
        }

        invalidate(drawableLeft,drawableTop, drawableRight,drawableBottom);
        try {
            if(isOpen){
                drawBitmapCanvas.drawText("关灯",left+(mBitmap.getWidth()/2)-TEXT_SIZE * density,drawableBottom+(int)(20* density),textPaint);
            }else{
                drawBitmapCanvas.drawText("开灯", left+(mBitmap.getWidth()/2)-TEXT_SIZE * density,drawableBottom+(int)(20* density),textPaint);
            }

        }catch (Exception e){
            e.printStackTrace();
        }
        //刷新文字区域
        invalidate(drawableLeft,drawableBottom+(int)(20* density), drawableRight,drawableBottom+(int)(45* density));
        drawBitmapCanvas.drawBitmap(mBitmap, mSrcRect, mDestRect, mBitPaint);


        isDraw = true;
    }

    public void drawViewfinder() {
        resultBitmap = null;
        invalidate();
    }

    /** * Draw a bitmap with the result points highlighted instead of the live * scanning display. * * @param barcode An image of the decoded barcode. */
    public void drawResultBitmap(Bitmap barcode) {
        resultBitmap = barcode;
        invalidate();
    }

    public void addPossibleResultPoint(ResultPoint point) {
        possibleResultPoints.add(point);
    }
}

适配各种尺寸屏幕
只要在CameraManager.java中修改尺寸：

  public Rect getFramingRect() {
   /* Point screenResolution = configManager.getScreenResolution();
    if (framingRect == null) {
      if (camera == null) {
        return null;
      }
      int width = screenResolution.x * 3 / 4;
      if (width < MIN_FRAME_WIDTH) {
        width = MIN_FRAME_WIDTH;
      } else if (width > MAX_FRAME_WIDTH) {
        width = MAX_FRAME_WIDTH;
      }
      int height = screenResolution.y * 3 / 4;
      if (height < MIN_FRAME_HEIGHT) {
        height = MIN_FRAME_HEIGHT;
      } else if (height > MAX_FRAME_HEIGHT) {
        height = MAX_FRAME_HEIGHT;
      }
      int leftOffset = (screenResolution.x - width) / 2;
      int topOffset = (screenResolution.y - height) / 2;
      framingRect = new Rect(leftOffset, topOffset, leftOffset + width, topOffset + height);
      Log.d(TAG, "Calculated framing rect: " + framingRect);
    }*/
    if (framingRect == null) {
      if (camera == null) {
        return null;
      }
      Point screenResolution = configManager.getScreenResolution();
      if (screenResolution == null) {
        // Called early, before init even finished
        return null;
      }

      // int width = findDesiredDimensionInRange(screenResolution.x,
      // MIN_FRAME_WIDTH, MAX_FRAME_WIDTH);
      // int height = findDesiredDimensionInRange(screenResolution.y,
      // MIN_FRAME_HEIGHT, MAX_FRAME_HEIGHT);

            /* 扫描框修改 */
      DisplayMetrics metrics = context.getResources().getDisplayMetrics();
      int width = (int) (metrics.widthPixels * 0.7);
      int height = (int) (width );

      int leftOffset = (screenResolution.x - width) / 2;
      int topOffset = (screenResolution.y - height) / 2;
      framingRect = new Rect(leftOffset, topOffset, leftOffset + width,
              topOffset + height);
      Log.d(TAG, "Calculated framing rect: " + framingRect);
    }

    return framingRect;
  }