android - 在现有图像上画一个圆圈

Question

我正在尝试在放置为res/drawable/schoolboard.png. 图像填充活动背景。以下不起作用：

    Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.schoolboard);
    Paint paint = new Paint();
    paint.setAntiAlias(true);
    paint.setColor(Color.BLUE);

    Canvas canvas = new Canvas(bitmap);
    canvas.drawCircle(60, 50, 25, paint);

    ImageView imageView = (ImageView)findViewById(R.drawable.schoolboard);
    imageView.setAdjustViewBounds(true);
    imageView.setImageBitmap(bitmap);

任何帮助将不胜感激。谢谢。

Answer 1

您的代码中有一些错误：首先，您不能为 drawable 提供参考 ID，findViewById 所以我认为您的意思是这样的

ImageView imageView = (ImageView)findViewById(R.id.schoolboard_image_view);

schoolboard_image_view是您的 xml 布局中的图像 ID（检查您的布局以获取正确的 ID）

BitmapFactory.Options myOptions = new BitmapFactory.Options();
    myOptions.inDither = true;
    myOptions.inScaled = false;
    myOptions.inPreferredConfig = Bitmap.Config.ARGB_8888;// important
    myOptions.inPurgeable = true;

    Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.schoolboard,myOptions);
    Paint paint = new Paint();
    paint.setAntiAlias(true);
    paint.setColor(Color.BLUE);


    Bitmap workingBitmap = Bitmap.createBitmap(bitmap);
    Bitmap mutableBitmap = workingBitmap.copy(Bitmap.Config.ARGB_8888, true);


    Canvas canvas = new Canvas(mutableBitmap);
    canvas.drawCircle(60, 50, 25, paint);

    ImageView imageView = (ImageView)findViewById(R.id.schoolboard_image_view);
    imageView.setAdjustViewBounds(true);
    imageView.setImageBitmap(mutableBitmap);

请确保将正确的图像 ID 用于：

ImageView imageView = (ImageView)findViewById( R.id.schoolboard_image_view );

Answer 2

首先你需要创建一个新的位图，因为来自 BitmapFactory.decodeResource() 方法的位图是不可变的。您可以使用以下代码执行此操作：

Bitmap canvasBitmap = Bitmap.createBitmap([bitmap_width], [bitmap_height], Config.ARGB_8888);

在 Canvas 构造函数中使用此位图。然后在画布上绘制您的位图。

Canvas canvas = new Canvas(canvasBitmap);
canvas.drawBitmap(bitmap, 0, 0, bitmapPaint);
canvas.drawCircle(60, 50, 25, paint);

R.drawable.schoolboard 也不是正确的视图 ID。

ImageView imageView = (ImageView)findViewById(R.drawable.schoolboard);