在位图上绘制文本失败

Question

我想在图像的顶部显示一个点和一个文本。我已经尝试过几个关于叠加位图的教程，但它似乎不起作用。这是显示背景图像的代码。

mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.roomplan);
mIV = (ImageView)findViewById(R.id.ImageView01);
mIV.setImageBitmap(mBitmap); 
mIV.invalidate();

btnDraw = (Button)findViewById(R.id.Button01);
btnDraw.setOnClickListener(this);

然后在OnClickListener上定义另一个位图并绘制点和文本。

Bitmap bmOverlay = Bitmap.createBitmap(mBitmap.getWidth(), mBitmap.getHeight(), 
    Bitmap.Config.ARGB_4444);
Canvas canvas = new Canvas(bmOverlay);
Paint paint = new Paint();
paint.setColor(Color.CYAN);
paint.setTextSize(20);
paint.setFlags(Paint.ANTI_ALIAS_FLAG);
canvas.drawText("You are here", 100, 100, paint);
canvas.drawPoint(30.0f, 50.0f, paint);
canvas.drawBitmap(bmOverlay, 0, 0, null);

即使当我删除图像时，也不会在背景图像的顶部显示任何内容。有什么提示吗？

更新：工作代码

// get a reference to the background image
mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.raumplan_isst);

mIV = (ImageView)findViewById(R.id.ImageView01);

// create a mutable bitmap with the same size as the background image
Bitmap bmOverlay = Bitmap.createBitmap(mBitmap.getWidth(), mBitmap.getHeight(), 
    Bitmap.Config.ARGB_4444);
// create a canvas on which to draw
canvas = new Canvas(bmOverlay);

Paint paint = new Paint();
paint.setColor(Color.CYAN);
paint.setTextSize(20);
paint.setFlags(Paint.ANTI_ALIAS_FLAG);

// if the background image is defined in main.xml, omit this line
canvas.drawBitmap(mBitmap, 0, 0, null);
// draw the text and the point
canvas.drawPoint(fKoordX, fKoordY, paint);
canvas.drawText("You are here", fKoordX+3, fKoordY+3, paint);

// set the bitmap into the ImageView
mIV.setImageBitmap(bmOverlay);

Answer 1

你拿帆布做什么？它在哪用的？(发布更多代码.)

此外，绘图顺序是错误的，您正在透支您的文本和点与位图。

编辑：

我有点迷茫，因为我不知道你的哪些图像应该是背景，你已经看到了什么图像.所以我猜mBitmap (房间计划)是你的背景吗？而不是将它作为背景图像添加到您的布局中，只需使用ImageView绘制覆盖层.

如果您的覆盖也需要背景图像，请尝试：

// overlay background
canvas.drawBitmap(myBmp, 0, 0, paint);
// draw the text and the point
canvas.drawText("You are here", 100, 100, paint);
canvas.drawPoint(30.0f, 50.0f, paint);

如果您的ImageView应该以房间计划为背景，请尝试：

// overlay background
canvas.drawBitmap(mBitmap, 0, 0, paint);
// draw the text and the point
canvas.drawText("You are here", 100, 100, paint);
canvas.drawPoint(30.0f, 50.0f, paint);