Draw text inside a filled rectangle using Canvas A

问题:

How to draw a filled rectangle with specified bounds and inside that rectangle text to be drawn using Canvas Android ?? I tried

mPaint.setColor(Color.GREEN);
canvas.drawText(mText, x, y, mPaint);
mPaint.setColor(Color.BLACK);
canvas.drawRect(x, y, x + w, y + h, mPaint);

but text is not inside of that rectangle. Can any buddy tell me how to draw a rectangle surrounding specified text with consideration of text size ??

回答1:

Here i have hardcoded x and y values. You can change them

        mpaint= new Paint();
        mpaint.setColor(Color.RED);
        mpaint.setStyle(Style.FILL);
        paint2= new Paint();
        paint2.setColor(Color.GREEN);
        paint2.setTextSize(50);  //set text size
        float w = paint2.measureText(s)/2;
        float textSize = paint2.getTextSize();


        @Override
        protected void onDraw(Canvas canvas) {
            paint2.setTextAlign(Paint.Align.CENTER);
            canvas.drawRect(300-w, 300 - textsize, 300 + w, 300, mpaint);
            canvas.drawText(s, 300, 300 ,paint2); //x=300,y=300    
        }

Edit :

Its bad a idea to call measureText in onDraw. You can do that outside of onDraw.

There is a video on also about performance and why you should avoid allocations in onDraw. https://www.youtube.com/watch?v=HAK5acHQ53E

Resulting snap shot

回答2:

This might be very late for this particular query but I think many will find this answer useful. So, the problem with the Canvas for any CustomView is that, you can get the width for a particular text, but it's not that easy to get the height of the text. Also if you are using canvas.drawText(....) with simple Paint object, you can not draw multi line text. So, use the below code within your onDraw() method.

String displayText = "Hello World";
int mainTextPositionX = getWidth() / 2 ;
int mainTextPositionY = getHeight() / 2;

StaticLayout textStaticLayout;
TextPaint textPaint;
textPaint = new TextPaint();
textPaint.setTextAlign(Paint.Align.CENTER);
textPaint.setColor(Color.BLUE);
textPaint.setAntiAlias(true);
textPaint.setTextSize(convertDpToPixel(30, context));
textPaint.setTextAlign(Paint.Align.CENTER);
highlightedRectPaint = new Paint();

highlightedRectPaint.setStrokeWidth(12);
highlightedRectPaint.setStyle(Paint.Style.STROKE);
highlightedRectPaint.setColor(Color.RED);
highlightedRectPaint.setAntiAlias(true);

if(android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.M) {
        textStaticLayout = StaticLayout
                .Builder
                .obtain(displayText, 0, displayText.length(), textPaint, (int) textPaint.measureText(displayText))
                .build();
    }else{
        textStaticLayout = new StaticLayout(
                displayText, textPaint, (int)textPaint.measureText(displayText), Layout.Alignment.ALIGN_CENTER, 1.0f, 0.0f, false);
    }

    Rect highlightedTextBorderRect = new Rect();
    highlightedTextBorderRect.top = mainTextPositionY-20;
    highlightedTextBorderRect.left = mainTextPositionX- 
    ((int)textPaint.measureText(displayText)/2)-20;
    highlightedTextBorderRect.right = mainTextPositionX+ 
    ((int)textPaint.measureText(displayText)/2) + 20;
    highlightedTextBorderRect.bottom = mainTextPositionY+ 
    (int)textStaticLayout.getHeight()+20;

    canvas.save();
    canvas.translate(mainTextPositionX, mainTextPositionY);
    textStaticLayout.draw(canvas);
    canvas.restore();

    canvas.drawRect(highlightedTextBorderRect,highlightedRectPaint);

just make sure that, you declare all the objects and variable outside of the draw() method. And this will draw a rectangle outline around the text with multi line support. If you want the rectangle to have a fill, then just use the highlightedRectPaint and change the setStyle(Paint.Style.FILL). Hope that helps.