如何在画布上设置图像.?然后在图像上绘制

Question

我想在白色画布上设置图像，并想在该图像上绘制，我不知道如何做到这一点。我尝试了所有可能的方法，但没有成功。这是我的代码。如果你想要其他代码，请告诉我。请帮我……

package com.example.drowingdemo;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.BitmapShader;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.Shader;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.MotionEvent;
import android.view.View;
public class DrawingView extends View {
	// drawing path
	private Path drawPath;
	// drawing and canvas paint
	private Paint drawPaint, canvasPaint;
	// initial color
	private int paintColor = 0xFF660000, paintAlpha = 255;
	// canvas
	private Canvas drawCanvas;
	// canvas bitmap
	private Bitmap canvasBitmap;
	// brush sizes
	private float brushSize, lastBrushSize;
	// erase flag
	private boolean erase = false;
	public DrawingView(Context context, AttributeSet attrs) {
		super(context, attrs);
		setupDrawing();
	}
	// setup drawing
	private void setupDrawing() {
		// prepare for drawing and setup paint stroke properties
		brushSize = getResources().getInteger(R.integer.medium_size);
		lastBrushSize = brushSize;
		drawPath = new Path();
		drawPaint = new Paint();
		drawPaint.setColor(paintColor);
		drawPaint.setAntiAlias(true);
		drawPaint.setStrokeWidth(brushSize);
		drawPaint.setStyle(Paint.Style.STROKE);
		drawPaint.setStrokeJoin(Paint.Join.ROUND);
		drawPaint.setStrokeCap(Paint.Cap.ROUND);
		canvasPaint = new Paint(Paint.DITHER_FLAG);
	}
	// draw the view - will be called after touch event
	@Override
	protected void onDraw(Canvas canvas) {
		canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);
		canvas.drawPath(drawPath, drawPaint);
	}
	// size assigned to view
	@Override
	protected void onSizeChanged(int w, int h, int oldw, int oldh) {
		super.onSizeChanged(w, h, oldw, oldh);
		canvasBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
		drawCanvas = new Canvas(canvasBitmap);
	}
	// register user touches as drawing action
	@Override
	public boolean onTouchEvent(MotionEvent event) {
		float touchX = event.getX();
		float touchY = event.getY();
		// respond to down, move and up events
		switch (event.getAction()) {
		case MotionEvent.ACTION_DOWN:
			drawPath.moveTo(touchX, touchY);
			break;
		case MotionEvent.ACTION_MOVE:
			drawPath.lineTo(touchX, touchY);
			break;
		case MotionEvent.ACTION_UP:
			drawPath.lineTo(touchX, touchY);
			drawCanvas.drawPath(drawPath, drawPaint);
			drawPath.reset();
			break;
		default:
			return false;
		}
		// redraw
		invalidate();
		return true;
	}
	// update color
	public void setColor(String newColor) {
		invalidate();
		// check whether color value or pattern name
		if (newColor.startsWith("#")) {
			paintColor = Color.parseColor(newColor);
			drawPaint.setColor(paintColor);
			drawPaint.setShader(null);
		} else {
			// pattern
			int patternID = getResources().getIdentifier(newColor, "drawable",
					"com.example.drowingdemo");
			// decode
			Bitmap patternBMP = BitmapFactory.decodeResource(getResources(),
					patternID);
			// create shader
			BitmapShader patternBMPshader = new BitmapShader(patternBMP,
					Shader.TileMode.REPEAT, Shader.TileMode.REPEAT);
			// color and shader
			drawPaint.setColor(0xFFFFFFFF);
			drawPaint.setShader(patternBMPshader);
		}
	}
	// set brush size
	public void setBrushSize(float newSize) {
		float pixelAmount = TypedValue.applyDimension(
				TypedValue.COMPLEX_UNIT_DIP, newSize, getResources()
						.getDisplayMetrics());
		brushSize = pixelAmount;
		drawPaint.setStrokeWidth(brushSize);
	}
	// get and set last brush size
	public void setLastBrushSize(float lastSize) {
		lastBrushSize = lastSize;
	}
	public float getLastBrushSize() {
		return lastBrushSize;
	}
	// set erase true or false
	public void setErase(boolean isErase) {
		erase = isErase;
		if (erase)
			drawPaint
					.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
		else
			drawPaint.setXfermode(null);
	}
	// start new drawing
	public void startNew() {
		drawCanvas.drawColor(0, PorterDuff.Mode.CLEAR);
		invalidate();
	}
	// return current alpha
	public int getPaintAlpha() {
		return Math.round((float) paintAlpha / 255 * 100);
	}
	// set alpha
	public void setPaintAlpha(int newAlpha) {
		paintAlpha = Math.round((float) newAlpha / 100 * 255);
		drawPaint.setColor(paintColor);
		drawPaint.setAlpha(paintAlpha);
	}
}

Answer 1

通过代码，我没有看到哪一行加载图像。

在您的代码中，Bitmap在方法onSizeChanged中被设置为Canvas，但该位图是一个空位图，您可以尝试使用该代码加载图像

@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    super.onSizeChanged(w, h, oldw, oldh);
    canvasBitmap = BitmapFactory.decodeResource(getResources(),R.drawable.your_image) //-->here load your image
                                .copy(Bitmap.Config.ARGB_8888, true); 
    drawCanvas = new Canvas(canvasBitmap);//-->set bitmap
}

此外，drawPath.reset（）在invalidate（）之前调用，在onDraw（）之前不要重置路径，

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        float touchX = event.getX();
        float touchY = event.getY();
        // respond to down, move and up events
        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            drawPath.moveTo(touchX, touchY);
            break;
        case MotionEvent.ACTION_MOVE:
            drawPath.lineTo(touchX, touchY);
            invalidate();
            break;
        case MotionEvent.ACTION_UP:
            drawPath.lineTo(touchX, touchY);
            drawPath = new Path();//--> use a new path after ACTION_UP
            break;
        default:
            return false;
        }
        // redraw
        drawCanvas.drawPath(drawPath, drawPaint);//--> Draw on canvasBitmap
        invalidate();
        return true;
    }
    @Override
    protected void onDraw(Canvas canvas)
    {
        canvas.drawBitmap(canvasBitmap, 0, 0, null);//--> draw canvasBitmap on canvas
        ...
    }