android 二维码扫描界面 canvas drawText 换行居中

今天做项目的时候用到了zxing扫描二维码功能，根据美工效果图，需要绘制字体，文字很长，并且要居中，网上搜了资料，终于实现了功能



zxing实现扫描二维码功能，请参考这篇博客

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修改ViewfinderView.java，实现上下扫描以及自定义扫描框

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

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，你要修改扫描框的大小，去CameraManager里面修改
Rect frame = CameraManager.get().getFramingRect();
if (frame == null) {
return;
}

//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 = "请将充电桩表面或者液晶屏幕上的二维码放入扫描框";
// 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 = "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, 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, (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);

}
}

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);
}