Develop Reference

Drawing line programmatically on a Layout

The red Margin represents an AbsoluteLayout, I have and arbitrary number of 'Board' objects placed on the screen. All I want is to draw a line on the screen using the coordinates of the Board object and the center of the screen. Each board object is responsible to draw this line.
Also I want the line to be behind the Board objects I'm guessing I have to change the z-index, or maybe draw the line on the AbsoluteLayout?
I have something like this:
public class Board {
ImageView line; //Imageview to draw line on
Point displayCenter; //Coordinates to the center of the screen
int x;
int y;
Activity activity;
Board(Point p, Point c, Activity activity) // Point c is the coordinates of the Board object
{
x = c.x
y = c.y
displayCenter.x = p.x;
displayCenter.y = p.y;
this.activity = activity;
updateLine();
}
public void updateLine(){
int w=activity.getWindowManager().getDefaultDisplay().getWidth();
int h=activity.getWindowManager().getDefaultDisplay().getHeight();
Bitmap bitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
line.setImageBitmap(bitmap);
Paint paint = new Paint();
paint.setColor(0xFF979797);
paint.setStrokeWidth(10);
int startx = this.x;
int starty = this.y;
int endx = displayCenter.x;
int endy = displayCenter.y;
canvas.drawLine(startx, starty, endx, endy, paint);
}
}

first af all,
you should never ever use the absolute layout, it is deprecated for a good reason.
With that said you have two options. For both options you need to implement your own Layout.
For option no. 1 you can override the dispatchDraw(final Canvas canvas) see below.
public class CustomLayout extends AbsoluteLayout {
...
#Override
protected void dispatchDraw(final Canvas canvas) {
// put your code to draw behind children here.
super.dispatchDraw(canvas);
// put your code to draw on top of children here.
}
...
}
Option no. 2 If you like the drawing to occur in the onDraw me you need to set setWillNotDraw(false); since by default the onDraw method on ViewGroups won't be called.
public class CustomLayout extends AbsoluteLayout {
public CustomLayout(final Context context) {
super(context);
setWillNotDraw(false);
}
...
#Override
protected void onDraw(final Canvas canvas) {
super.onDraw(canvas);
// put your code to draw behind children here.
}
}

How to create graph with edges and vertices in Android

I want to create graph (with edges and vertices), to implement a problem called 3-color. I just need a little guidance on how to start, should i use a multiple views and draw each view as a circle, and then how can i connect lines (edges) between the views? should i work with pixels all the time or there is another way, more simple one because calculate pixels when dealing with big graphs (more than 10 vertices) is complicated.
thanks.

What you want is called drawing on Canvas.
As a basic example you can see this code, which will create 2 vertices and an edge connecting them:
public class MyView extends View {
private final Paint p;
private final Path path;
private final Point point1;
private final Point point2;
public MyView(Context context) {
super(context);
p = new Paint(Paint.ANTI_ALIAS_FLAG);
p.setStrokeWidth(10);
path = new Path();
point1 = new Point(200, 300);
point2 = new Point(700, 800);
}
#Override
protected void onDraw(Canvas canvas) {
// draw first vertex
p.setStyle(Paint.Style.FILL);
p.setColor(Color.GREEN);
canvas.drawCircle(point1.x, point1.y, 15, p);
// draw the edge
path.reset();
path.moveTo(point1.x, point1.y);
path.lineTo(point2.x, point2.y);
p.setStyle(Paint.Style.STROKE);
p.setColor(Color.CYAN);
canvas.drawPath(path, p);
// draw second vertex
p.setStyle(Paint.Style.FILL);
p.setColor(Color.BLUE);
canvas.drawCircle(point2.x, point2.y, 15, p);
}
}
Which will result in this:

I found this library which is a good source:
https://github.com/LordVulkan/Graphs

Connect the dots of an imageview

It is a difficult task to create an app for kids and i am given a task of creating an connect the dots app.
example
https://play.google.com/store/apps/details?id=zok.android.dots
i have done some tutorials of onTouchEvent.
i know how to paint on screen Draw in Canvas by finger, Android
i am getting the dot coordinates using this Android: How do I get the x y coordinates within an image / ImageView? example
but I really don't know how to achieve this target.
I'd really appreciate a solution to this! Thanks!
input image is http://imgur.com/Z24yQUx,t6nL71r
EDIT
#Override
protected void onDraw(Canvas canvas) {
//backgroundBitmap is the image i want to show in background
if(DISPLAY_ALPHABET==0)
{
canvas.drawBitmap(backgroundBitmap, 0f, 0f, null);
DISPLAY_ALPHABET=1;
}
show(canvas);
}
public void show(Canvas canvas)
{
Paint paint = new Paint();
int cnt=1;
canvas.drawPaint(paint);
//color of numbers
paint.setColor(Color.BLUE);
paint.setTextSize(16);
canvas.drawColor(BACKGROUND);
** canvas.drawBitmap(mBitmap, 0, 0, null);**
canvas.drawPath(mPath, mPaint);
mPaint.setColor(Color.BLACK);
//Drawing points on canvas
for (Point point : mPoints) {
canvas.drawPoint(point.x, point.y, mPaint);
canvas.drawText(""+cnt++, point.x-7, point.y-7, paint);
}
mPaint.setColor(Color.RED);
}

I don't have much idea about this but still felt like worth thinking
You can save the next dot coordinates in a arraylist or a vector.
when you are drawing the line using canvas, check whether the Motion-Event x and y coordinates matches to that of the next point in the vector.
Once a coordinate is touched search for the next one in the vector
You can use a counter to increase the vector position, once the dot touched increment the counter.
EDIT: Check out my Demo App in this Link and check what you might need.

How to move a bitmap from one coordinate to another - Android development

I want to move a bitmap image along consecutive coordinates in SurfaceView. I have a bitmap myBall drawn in the coordinate (x1, y1) on a SurfaceView as follows (partial code)(
public class MainSurfaceView extends SurfaceView implements Runnable {...
...
#Override
public void run() {
while (isRunning) {
if (!myHolder.getSurface().isValid())
continue;
Canvas canvas;// Define canvas to paint on it
canvas = myHolder.lockCanvas();
//Draw full screen rectangle to hold the floor map.
Rect dest = new Rect(0, 0, getWidth(), getHeight());
Paint paint = new Paint();
paint.setFilterBitmap(true);
canvas.drawBitmap(bgImage, null, dest, paint);
//This is the ball I want to move
canvas.drawBitmap(myBall, x1, y1, null);
myHolder.unlockCanvasAndPost(canvas);
}
}
Now I want to move it to (x2, y2) then (x3, y3) and ... as many as needed and one after the other. I have tried to use TranslateAnimation but couldn't do it.

I have figured out how to animate using a coordinates. I will explain what I did hopping that it will be helpful to others:
First I saved the coordinates as Point object
List<Point> point_list = new ArrayList<Point>();
point_list.add(new Point(x_value, y_value));//Add the x and y coordinates to the Point\
Leave implementing Runnable and use onDraw() method instead of run() method as follows:
public class MainSurfaceView extends SurfaceView {...
....
#Override
protected void onDraw(Canvas canvas) {
// Draw full screen rectangle to hold the floor map.
Rect fArea = new Rect(0, 0, getWidth(), getHeight());
Paint paint = new Paint();
paint.setFilterBitmap(true);
// draw the paint on the rectangle with the floor map
canvas.drawBitmap(bgImage, null, fArea, paint);
// Get the coordinates of x & y as Point object
List<Point> myPoints = point_list;
// Start printing myBall on the floor (view)
try {
if (index < myPoints.size()) {
// Increment the value of index and use it as index for the point_list
index++;
}
// Print myBall in each coordinates of x & y using the index
canvas.drawBitmap(myBall, myPoints.get(index).x, myPoints.get(index).y, null);
} catch (IndexOutOfBoundsException e) {
// TODO: handle exception
}
}
I use try and catch to avoid IndexOutOfBoundryExeption
Cheers!

I think this might be what you're after. What you're trying to do is tween the bitmap and there are a few ways you can do that. There is also the ViewPropertyAnimator, which can animate an entire view.

Draw Circle at Center of Canvas

I'm just getting into basic drawing with Android. I'm starting off with a few simple shapes but I'm having a few issues. I'd like to draw a circle at the center of a canvas. I looked at a few examples but can't seem to make it work. I think it's because I don't really understand what variables go where.
Could someone please explain the proper way to draw my circle at the center of my screen. Here is my code:
public class Circle extends View{
int width = this.getWidth();
int height = this.getHeight();
public Circle(Context context) {
super(context);
setFocusable(true);
}
protected void onDraw(Canvas canvas){
canvas.drawColor(Color.CYAN);
Paint paint = new Paint();
paint.setStyle(Paint.Style.FILL);
//canvas.drawCircle(100, 100, 50, paint);
canvas.drawCircle(width/2, height/2, 100, paint);
Display disp = ((WindowManager)this.getContext().getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay();
float radius = 0;//Radius caused an error so I initialized this variable
canvas.drawCircle(disp.getWidth()/2, disp.getHeight()/2, radius, paint);
}
}

width and height of the view have not been yet initialized when getWidth() and getHeight() are called, just use getWidth() and getHeight() in onDraw:
canvas.drawCircle(getWidth()/2, getHeight()/2, 100, paint);
You can also override onSizeChanged and get view width and height.
PS: do not create anything in onDraw, create the paint object in the constructor.

public void drawCircle(Graphics2D g, int x, int y, int radius) {
x = x-(radius/2);
y = y-(radius/2);
g.fillOval(x,y,radius,radius);
}
here x,y is the position of canvas where you want to draw circle and you can find it with motion listener if you want to set x,y position dynamically hope this will help you

There are some links which are very useful for us and I hope they will work for you and other.
https://github.com/swapgo20/Android-Hand-Drawing
https://github.com/codepath/android_guides/wiki/Basic-Painting-with-Views
https://github.com/Korilakkuma/CanvasView
I hope above links are very useful to draw shapes on canvas.
I suggest you use third link and use only Path class (http://developer.android.com/reference/android/graphics/Path.html) of android to draw shapes.