Develop Reference

Is it possible to invalidate Text only, but not background image on a custom View on android?

My CustomView draws some polygons and the title text is located at the centre of a view. As the application runs, I need to change the title text of these views frequently. Of course, I can invalidate after setting a new text so that the application will redraw everything - polygons, colors, and finally the new text - but I am just wondering if there is a clever way that only invalidates the title text, leaving all background polygons untouched. The current code looks like this:
public CustomView extends View {
private Path mPolygon1;
private Path mPolygon2;
// .. more polygons
private String mTitleText;
#Override
protected void onDraw(Canvas canvas) {
// Draws all images
canvas.drawPath(mPolygon1, mPaint);
canvas.drawPath(mPolygon2, mPaint);
// ... more polygon drawing
canvas.drawText(mTitleText, 0, mTitleText.length(), mTextPaint);
}
public void setTitle(String title) {
mTitleText = title;
invalidate(); // more clever way????
}
}

You can use invalidate(Rect) or invalidate(left, top, right, bottom)
Here is a link for more details

onDraw method not drawing everything I put in to it

I have created a custom view class to use in a project I'm working on. To put is simply, I'm displaying an image, then adding images on top of the original image (currently by clicking on the image, but that's not final).
I have these 2 methods in my custom view:
protected void onDraw(Canvas canvas)
{
super.onDraw(canvas);
for (Drawable d : drawableList)
{
d.draw(canvas);
}
}
public void AddPoint(float x, float y)
{
Drawable tempDrawable = pin;
tempDrawable.setBounds((int)x, (int)y, (int)x + 50, (int)y + 50);
drawableList.add(tempDrawable);
invalidate();
}
The AddPoint() method is called in an OnTouchListener and is passes the coordinates of the touch event.
The way it currently works is it displays the main image, but will only display the most recent images where I clicked, previous ones just disappear.
Does anybody know what I am doing wrong here?

I've figured out what I was doing wrong.
The line of code:
Drawable tempDrawable = pin;
I changed to:
Drawable tempDrawable = mainRes.getDrawable(R.drawable.pin);
I got mainRes from the init(Context context) method I wrote in the custom View class.

Applying a BitmapShader using relative coordinates when using canvas.drawBitmap

I'm trying to Use a BitmapShader to draw on a Canvas. I have 2 images of the same dimensions (one for the alfa channel and one for RGB), that I want to draw on a canvas that was created with the same size. The problem is that it seem as though canvas.drawBitmap users absolute coordinates for the paint. is there a way to draw with relative coordinates.
public class MaskedImageDrawable extends Drawable {
private final Bitmap mMask;
private final Paint mPaint = new Paint();
public MaskedImageDrawable(Bitmap mask, Bitmap image) {
mMask = mask;
Shader targetShader =
new BitmapShader(image, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
mPaint.setShader(targetShader);
}
#Override
public void draw(Canvas canvas) {
canvas.drawBitmap(mMask, 0.0f, 0.0f, mPaint);
}
#Override
public int getOpacity() {
return PixelFormat.TRANSLUCENT;
}
#Override
public void setAlpha(int alpha) {
mPaint.setAlpha(alpha);
}
#Override
public void setColorFilter(ColorFilter cf) {
mPaint.setColorFilter(cf);
}
}
I can't seem to be able to get the drawable's absolute coordinates on the screen. I know I can use getLocationOnScreen/InWindow from the view that holds the drawable but that doesn't take animations into account.
I tried tried applying relative coordinates by applying a translation on the shader in onBoundsChange but the coordinates here seems to be relative as well.
Matrix mTranslationMatrix = new Matrix()
#Override
protected void onBoundsChange(Rect bounds) {
super.onBoundsChange(bounds);
mTranslationMatrix.setTranslate(bounds.left, bounds.top);
mPaint.getShader().setLocalMatrix(mTranslationMatrix);
}
As a reference - it seems drawRect with the same paint will use relative coordinates. so replacing the draw method with the following will render the RGB image on the drawable correctly (but not the mask)
#Override
public void draw(Canvas canvas) {
// getBounds returns the relative coordinates as well
canvas.drawRect(getBounds, mPaint);
}

It seems that this is a HW acceleration issue. disabling HW acceleration on the view moves the shader back to relative coordinates.
if (android.os.Build.VERSION.SDK_INT >= 11) {
myView.disableHwAcceleration();
}

Rounded corners drawable via code

I have a drawable that will change colors sometimes, but it must ALWAYS have rounded corners. It's for a UI library, so I can't know what colors will it have. XML is not an option, I have to achieve this with pure java.
Is there a way to achieve this programatically WITHOUT using XML?

Create a custom Drawable (i.e. extend Drawable) and in its onDraw use Canvas.drawRoundRect(RectF rect, float rx, float ry, Paint paint), setting the Paint to the desired colour.

If you draw the drawable by yourself, you could set a clip path with Canvas.clipPath. The path would consist of one or more rectangles and some circles, which clip the rounded corners. You probably have to play around with the arrangement of the path components until you get the desired output.

Based on the answer from #nmw, here's some code that works for this:
public class RRDrawable extends Drawable {
private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
public RRDrawable(int color) {
paint.setColor(color);
paint.setStyle(Paint.Style.FILL);
}
#Override
public void draw(Canvas canvas) {
int radius = 10; // note this is actual pixels
canvas.drawRoundRect(new RectF(0,0,canvas.getWidth(), canvas.getHeight()), radius, radius, paint);
}
#Override
public void setAlpha(int i) {
//.. not supported
}
#Override
public void setColorFilter(ColorFilter colorFilter) {
//.. not supported
}
#Override
public int getOpacity() {
return 1;
}
}
EDIT: added anti-aliasing to the edges.
(source)

Android OnTouch events numerous Objects

ok I'm playing w/ ontouch events extending a view.
what I've done is made a circle on touch.. the cirlce will follow as you move. As you move another circle is made and will sit in the postion decrementing the radius until it disappears.. (right now up to like 10 circles). I can also handle multiple fingers touching at one point in time. Here's the problem.. THE CODE IS NASTY!
To create multiple circle This is my paint method:
public void onDraw(Canvas canvas)
{
paint.setColor(Color.RED);
paint.setStyle(Style.STROKE);
paint.setStrokeWidth(stroke);
canvas.drawCircle(x,y,radius,paint);
canvas.drawCircle(x1,y1,radius1,paint);
canvas.drawCircle(x2,y2,radius2,paint);
canvas.drawCircle(x3,y3,radius3,paint);
canvas.drawCircle(x4,y4,radius4,paint);
canvas.drawCircle(x5,y5,radius5,paint);
canvas.drawCircle(x6,y6,radius6,paint);
paint.setColor(Color.BLUE);
canvas.drawCircle(x7,y7,radius7,paint);
canvas.drawCircle(x8,y8,radius8,paint);
paint.setColor(Color.YELLOW);
canvas.drawCircle(x9,y9,radius9,paint);
canvas.drawCircle(x10,y10,radius10,paint);
}
so as you can see this by far inefficient and makes for some long nasty code.. Part of the issue is the fact I'm bound to only being able to change coordinates in Ontouch.. and invalidate. Anyoone know a way I can do this more efficently (in a more object orriented type approach).

First things first, start with this:
public class Circle {
public int x;
public int y;
public double radius;
public Paint paint;
/* constructors, getters & setters if you feel like ...*/
}
And put all your circles in a
ArrayList<Circle> circles = new ArrayList();
public void onDraw(Canvas canvas)
{
/*...*/
Iterator iterator = circles.iterator();
while(iterator.hasNext()) {
drawCircle(iterator.next());
}
}
public void drawCircle(Canvas canvas, Circle circle) {
canvas.drawCircle(circle.x, circle.y, circle.raidus, circle.paint);
}