如何在Canvas ..上设置图像？ 然后在图像上绘制

Question

i want to set image on white canvas and want to draw on that image i don't know how to do that. i tried all possible method, but not work. this is my code help me if u want any other code then tell me. and please help me......

 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

Through the code, I didn't see which line loads an image.

In your code, Bitmap is set for Canvas in method onSizeChanged, but the bitmap is an empty bitmap, you may try the code to load image

@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
}

In addition, drawPath.reset() is called before invalidate(), do not reset path before onDraw(),

    @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
        ...
    }