如何在画布上绘制文字？

Question

i'm trying to develop a simple pie chart class for android. For now, it can take a map of labels and values and draw the pie chart. I'm yet to add the legends for the pie, which is where i need to place the texts near small rectangles on the screen corner. Any help appreciated, since i'm new to Android dev.

Answer 1

You will have to use the drawText method of the Canvas class.

Paint paint = new Paint(); 
canvas.drawPaint(paint); 
paint.setColor(Color.BLACK); 
paint.setTextSize(16); 
canvas.drawText("My Text", x, y, paint); 

Here's the relevant documentation about it:

http://developer.android.com/reference/android/graphics/Canvas.html#drawText(java.lang.String, float, float, android.graphics.Paint)

Answer 2

There used to be another answer here that got deleted because it was a link only. The original link is here . The code is basically the same, but I took out the non text drawing portions and also scaled up the sizes to work better on modern screen densities.

This just shows a few things you can do with text drawing.

Here is the updated code:

public class MainActivity extends AppCompatActivity {

    DemoView demoview;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        demoview = new DemoView(this);
        setContentView(demoview);
    }

    private class DemoView extends View {
        public DemoView(Context context){
            super(context);
        }

        @Override protected void onDraw(Canvas canvas) {
            super.onDraw(canvas);

            // custom drawing code here
            // remember: y increases from top to bottom
            // x increases from left to right
            int x = 0;
            int y = 0;
            Paint paint = new Paint();
            paint.setStyle(Paint.Style.FILL);

            canvas.save();
            canvas.translate(100, 200);

            // make the entire canvas white
            canvas.drawColor(Color.WHITE);

            // draw some text using STROKE style
            paint.setStyle(Paint.Style.STROKE);
            paint.setStrokeWidth(1);
            paint.setColor(Color.MAGENTA);
            paint.setTextSize(100);
            canvas.drawText("Style.STROKE", 0, 0, paint);

            canvas.translate(0, 200);

            // draw some text using FILL style
            paint.setStyle(Paint.Style.FILL);
            //turn antialiasing on
            paint.setAntiAlias(true);
            //paint.setTextSize(30);
            canvas.drawText("Style.FILL", 0, 0, paint);

            canvas.translate(0, 200);

            // draw some rotated text
            // get text width and height
            // set desired drawing location
            x = 75;
            y = 185;
            paint.setColor(Color.GRAY);
            //paint.setTextSize(25);
            String str2rotate = "Rotated!";

            // draw bounding rect before rotating text
            Rect rect = new Rect();
            paint.getTextBounds(str2rotate, 0, str2rotate.length(), rect);
            canvas.translate(x, y);
            paint.setStyle(Paint.Style.FILL);
            // draw unrotated text
            canvas.drawText("!Rotated", 0, 0, paint);
            paint.setStyle(Paint.Style.STROKE);
            canvas.drawRect(rect, paint);
            // undo the translate
            canvas.translate(-x, -y);

            // rotate the canvas on center of the text to draw
            canvas.rotate(-45, x + rect.exactCenterX(),
                    y + rect.exactCenterY());
            // draw the rotated text
            paint.setStyle(Paint.Style.FILL);
            canvas.drawText(str2rotate, x, y, paint);

            //undo the translation and rotation
            canvas.restore();
        }
    }
}

Something else that I want to try later is drawing text along a path .

See also this fuller answer here that gives the following image.

Answer 3

Another (arguably better) way to draw text on a canvas is to use a StaticLayout . This handles multiline text when needed.

String text = "This is some text.";

TextPaint textPaint = new TextPaint();
textPaint.setAntiAlias(true);
textPaint.setTextSize(16 * getResources().getDisplayMetrics().density);
textPaint.setColor(0xFF000000);

int width = (int) textPaint.measureText(text);
StaticLayout staticLayout = new StaticLayout(text, textPaint, (int) width, Layout.Alignment.ALIGN_NORMAL, 1.0f, 0, false);
staticLayout.draw(canvas);

The TextPaint and StaticLayout were instantiated right before being used here for the sake of illustration. Doing so in onDraw would hurt performance, though. Here is a better example showing them in the context of a custom view that draws it's own text.