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 = 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
        int left =frame.left+(frame.right-frame.left)/2- mBitmap.getWidth() / 2;
        // 计算上边位置
        int top = frame.bottom +  (int)(TEXT_PADDING_TOP * 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);
        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);
    }
}