How to make any view to draw to canvas?

Question

I have a short question:

Suppose I have a (mutable) bitmap that I need to modify (add images, texts, etc...) .

Instead of messing around with many special classes for drawing to the canvas (paint, canvas, matrices and so on), I was thinking why not use the built in classes of Android for this task and only if i need really customized operations i could still use the canvas ?

So, for example, in order to show any kind of view (that has no parent, of course) on the bitmap, I could call the next function :

public void drawViewToBitmap(Bitmap b, View v, Rect rect) {     Canvas c = new Canvas(b);     // <= use rect to let the view to draw only into this boundary inside the bitmap     view.draw(c); } 

Is such a thing possible? maybe that's even the way that it works behind the scenes?

what should i write in the part between the drawing and the creation of the canvas?

---

EDIT: i've tried the next code , but it didn't work:

public void drawFromViewToCanvas(final View view, final Rect rect, final Canvas canvas) {     final int widthSpec = View.MeasureSpec.makeMeasureSpec(rect.width(), View.MeasureSpec.EXACTLY);     final int heightSpec = View.MeasureSpec.makeMeasureSpec(rect.height(), View.MeasureSpec.EXACTLY);     view.measure(widthSpec, heightSpec);     // Lay the view out with the known dimensions     view.layout(0, 0, rect.width(), rect.height());     // Translate the canvas so the view is drawn at the proper coordinates     canvas.save();     canvas.translate(rect.left, rect.top);     // Draw the View and clear the translation     view.draw(canvas);     canvas.restore(); } 

example of usage:

final int imageSize = 50; rect = new Rect(35, 344 , 35 + imageSize, 344  + imageSize); final ImageView imageView = new ImageView(mContext); imageView.setImageBitmap(bitmap); imageView.setScaleType(ScaleType.CENTER_CROP); drawFromViewToCanvas(imageView, getRect(), canvas); 

---

EDIT: there is a sample on sony's website:

int measureWidth = View.MeasureSpec.makeMeasureSpec(bitmapWidth, View.MeasureSpec.EXACTLY); int measuredHeight = View.MeasureSpec.makeMeasureSpec(bitmapHeight, View.MeasureSpec.EXACTLY); view.measure(measureWidth, measuredHeight); view.layout(0, 0, bitmapWidth, bitmapHeight); view.draw(canvas); 

wonder if it works.

Answer 1

Yeah, you can do this. Keep in mind, since you're not attaching it to a layout, you'll need to lay it out manually before drawing it:

view.layout(0, 0, viewWidth, viewHeight); 

And unless you just know exactly what you want for those width and height parameters, you may also want to measure it first:

int widthSpec = MeasureSpec.makeMeasureSpec (ViewGroup.LayoutParams.WRAP_CONTENT, MeasureSpec.UNSPECIFIED; int heightSpec = MeasureSpec.makeMeasureSpec (400, MeasureSpec.UNSPECIFIED; view.measure(widthSpec, heightSpec); view.layout(0, 0, view.getMeasuredWidth(), view.getMeasuredHeight()); 

EDIT:

If you already know the width and height you need:

//Lay the view out with the known dimensions view.layout (0, 0, rect.width(), rect.height());  //Translate the canvas so the view is drawn at the proper coordinates canvas.save(); canvas.translate(rect.left, rect.top);  //Draw the View and clear the translation view.draw(canvas); canvas.restore(); 

EDIT again:

Yes, tested. You can try this yourself:

public class DrawingActivity extends Activity {     public void onCreate (Bundle savedInstanceState) {         super.onCreate(savedInstanceState);          //Set a Rect for the 200 x 200 px center of a 400 x 400 px area         Rect rect = new Rect();         rect.set(100, 100, 300, 300);          //Allocate a new Bitmap at 400 x 400 px         Bitmap bitmap = Bitmap.createBitmap(400, 400, Bitmap.Config.ARGB_8888);         Canvas canvas = new Canvas(bitmap);          //Make a new view and lay it out at the desired Rect dimensions         TextView view = new TextView(this);         view.setText("This is a custom drawn textview");         view.setBackgroundColor(Color.RED);         view.setGravity(Gravity.CENTER);          //Measure the view at the exact dimensions (otherwise the text won't center correctly)         int widthSpec = View.MeasureSpec.makeMeasureSpec(rect.width(), View.MeasureSpec.EXACTLY);         int heightSpec = View.MeasureSpec.makeMeasureSpec(rect.height(), View.MeasureSpec.EXACTLY);         view.measure(widthSpec, heightSpec);          //Lay the view out at the rect width and height         view.layout(0, 0, rect.width(), rect.height());          //Translate the Canvas into position and draw it         canvas.save();         canvas.translate(rect.left, rect.top);         view.draw(canvas);         canvas.restore();          //To make sure it works, set the bitmap to an ImageView         ImageView imageView = new ImageView(this);         imageView.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));         setContentView(imageView);         imageView.setScaleType(ImageView.ScaleType.CENTER);         imageView.setImageBitmap(bitmap);     } }