绘制到 ImageView

Question

我已经研究了几个小时的 Androidreference，但并没有真正了解如何在 ImageView 上绘制一些东西（文本、位图、路径 ....）。

我应该扩展 View 并使用onDraw()-方法吗？如果是，我如何在 ImageView 上绘图？

或者还有其他方法可以实现我的目标吗？

Answer 1

如果您只想在 ImageView 上绘制另一个位图并且它不应该是动态的，那么请使用 AbsoluteLayout 并将它们放在彼此之上。

如果它应该更加动态，我建议使用 SurfaceView。教程可以在这里找到：http://www.droidnova.com/playing-with-graphics-in-android-part-i,147.html

（目前仅通过网络存档在线：http://web.archive.org/web/20121005111921/http://www.droidnova.com/2d-tutorial-series）

Answer 2

是的，您可以使用 onDraw 方法。有一个 Canvas 对象传递到该方法中，您将使用它在视图上绘制。这是一个如何做到这一点的示例...取自斑马线条形码扫描仪应用程序。它是显示深色外框、红色扫描线和黄色扫描结果点的视图。

@Override
public void onDraw(Canvas canvas) {
    Rect frame = CameraManager.get().getFramingRect();
    if (frame == null) {
      return;
    }
    int width = canvas.getWidth();
    int height = canvas.getHeight();
    Log.v("ViewfinderView", "Canvas size: " + width + ", " + height);

    // Draw the exterior (i.e. outside the framing rect) darkened
    paint.setColor(resultBitmap != null ? resultColor : maskColor);
    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 {

      // Draw a two pixel solid black border inside the framing rect
      paint.setColor(frameColor);
      canvas.drawRect(frame.left, frame.top, frame.right + 1, frame.top + 2, paint);
      canvas.drawRect(frame.left, frame.top + 2, frame.left + 2, frame.bottom - 1, paint);
      canvas.drawRect(frame.right - 1, frame.top, frame.right + 1, frame.bottom - 1, paint);
      canvas.drawRect(frame.left, frame.bottom - 1, frame.right + 1, frame.bottom + 1, paint);

      // Draw a red "laser scanner" line through the middle to show decoding is active
      paint.setColor(laserColor);
      paint.setAlpha(SCANNER_ALPHA[scannerAlpha]);
      scannerAlpha = (scannerAlpha + 1) % SCANNER_ALPHA.length;
      int middle = frame.height() / 2 + frame.top;
      canvas.drawRect(frame.left + 2, middle - 1, frame.right - 1, middle + 2, paint);

      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);
        }
      }

      // Request another update at the animation interval, but only repaint the laser line,
      // not the entire viewfinder mask.
      postInvalidateDelayed(ANIMATION_DELAY, frame.left, frame.top, frame.right, frame.bottom);
    }
  }

Answer 3

SurfaceView 是你想要的。它会给你一个Canvas 对象，你可以使用canvas.drawCircle(...)、canvas.drawText(...)、canvas.drawBitamp(...) 在其上绘图。