Develop Reference

Android: How do I separate it into 2 class?

I read a tutorial online about drawing a Circle (1st part of tutorial):
Introduction to 2D drawing in Android with example
I got it worked. Now I want to separate them into 2 classes:
MainActivity.java
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(new SimpleView(this));
}
}
SimpleView.java
public class SimpleView extends SurfaceView {
public SimpleView(Context context) {
super(context);
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
int x = getWidth();
int y = getHeight();
int radius;
radius = 100;
Paint paint = new Paint();
paint.setStyle(Paint.Style.FILL);
paint.setColor(Color.GREEN);
canvas.drawPaint(paint);
// Use Color.parseColor to define HTML colors
paint.setColor(Color.parseColor("#CD5C5C"));
canvas.drawCircle(x / 2, y / 2, radius, paint);
}
}
However, I wasn't able to get them work: it never draws anything.
What did I do wrong here?

If you want to use a SurfaceView you can, all you need to do is to call setWillNotDraw(false) on the constructor so the class will look like this:
public class SimpleView extends SurfaceView {
public SimpleView(Context ctx) {
super(ctx);
setWillNotDraw(false); //notice this method call IMPORTANT
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
int x = getWidth();
int y = getHeight();
int radius;
radius = 100;
Paint paint = new Paint();
paint.setStyle(Paint.Style.FILL);
paint.setColor(Color.GREEN);
canvas.drawPaint(paint);
// Use Color.parseColor to define HTML colors
paint.setColor(Color.parseColor("#CD5C5C"));
canvas.drawCircle(x / 2, y / 2, radius, paint);
}
}

Draw multiple rectangles android canvas

I'm trying to draw 4 rectangles on the canvas so that the canvas is divided in 4 equal rectangles. With the code I now have, only the last rectangle in my code is drawn.
This is the code in my Activity:
protected void onCreate(Bundle savedInstanceState) {
...
setContentView(new MyView(this));
}
public class MyView extends View {
public MyView(Context context) {
super(context);
// TODO Auto-generated constructor stub
setFocusableInTouchMode(true);
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
int x = getWidth();
int y = getHeight();
Paint paintTopLeft = new Paint();
paintTopLeft.setStyle(Paint.Style.FILL);
paintTopLeft.setColor(Color.WHITE);
canvas.drawPaint(paintTopLeft);
// Use Color.parseColor to define HTML colors
paintTopLeft.setColor(Color.parseColor("#F44336"));
canvas.drawRect(0,0,x / 2,y / 2,paintTopLeft);
Paint paintTopRight = new Paint();
paintTopRight.setStyle(Paint.Style.FILL);
paintTopRight.setColor(Color.WHITE);
canvas.drawPaint(paintTopRight);
// Use Color.parseColor to define HTML colors
paintTopRight.setColor(Color.parseColor("#2196F3"));
canvas.drawRect(x / 2, 0, x, y / 2, paintTopRight);
}
}
What am I doing wrong?

Actually I see only two rectangles that are drawn with your code. But anyway, the problem is that you are calling canvas.drawPaint which clears/fills the complete canvas with that color. So you are erasing all rectangles that have been drawn already just before you draw the last one.
This code should work:
protected void onCreate(Bundle savedInstanceState) {
...
setContentView(new MyView(this));
}
public class MyView extends View {
public MyView(Context context) {
super(context);
// TODO Auto-generated constructor stub
setFocusableInTouchMode(true);
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
int x = getWidth();
int y = getHeight();
Paint paintTopLeft = new Paint();
paintTopLeft.setStyle(Paint.Style.FILL);
paintTopLeft.setColor(Color.WHITE);
//canvas.drawPaint(paintTopLeft); // don't do that
// Use Color.parseColor to define HTML colors
paintTopLeft.setColor(Color.parseColor("#F44336"));
canvas.drawRect(0,0,x / 2,y / 2,paintTopLeft);
Paint paintTopRight = new Paint();
paintTopRight.setStyle(Paint.Style.FILL);
paintTopRight.setColor(Color.WHITE);
// canvas.drawPaint(paintTopRight); // don't do that
// Use Color.parseColor to define HTML colors
paintTopRight.setColor(Color.parseColor("#2196F3"));
canvas.drawRect(x / 2, 0, x, y / 2, paintTopRight);
}
}

Drawing animate line on Canvas of a View

I simply need to draw a line which moves from one coordinate of a canvas to another. I am having troubles with synchronizing my drawing code with time.\
public class CustomMYChart extends View {
float x=0,y=0;
Canvas canvas;
Paint paint;
public CustomMYChart(Context context) {
super(context);
// TODO Auto-generated constructor stub
paint = new Paint();
paint.setColor(Color.GREEN);
}
#Override
protected void onDraw(final Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
this.canvas=canvas;
for(int i=0; i<1000; i++){
canvas.drawCircle(x, y, 5, paint);
x+=1;
y+=1;
invalidate();
}
}
}

Just remove the for statement in onDraw, with just one for iteration you call 1000 times invalidate() and then you get x and y out of the screen.
#Override
protected void onDraw(final Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
this.canvas=canvas;
canvas.drawCircle(x, y, 5, paint);
x+=1;
y+=1;
invalidate();
}

How to set android xml layout to custom view and be able to draw on it

I want to add xml layout to custom view. It is done in commented section of code. But I am not able to draw after doing that. This Code paint red circle in center of screen. After uncommenting commented lines circle is not painted.
public class Main extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(new MyView(this));
}
public class MyView extends View {
Paint paint;
public MyView(Context context) {
super(context);
// View view = inflate(context, R.layout.activity_main_zadanie, null);
// view.setFocusable(true);
// addView(view);
paint = new Paint();
}
#Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
int x = getWidth();
int y = getHeight();
int radius;
radius = 100;
paint.setStyle(Paint.Style.FILL);
paint.setColor(Color.WHITE);
canvas.drawPaint(paint);
// Use Color.parseColor to define HTML colors
paint.setColor(Color.parseColor("#CD5C5C"));
canvas.drawCircle(x / 2, y / 2, radius, paint);
}
}
}

Your new view is probably covering the canvas on your custom view. Try setting the background to translucent in R.layout.activity_main_zadanie.

Use of constant in Canvas.drawLine()

I have this code.
Only the first drawLine gets drawn and the rest 2 are not. Can anyone explain why the other two drawlines do not work in the present case?
They work if I replace "factor" with "1/2" in the drawLine() statements.
Thanks
public class RenderView extends View {
Paint paint;
private float factor = 1/2;
public RenderView(Context context) {
// TODO Auto-generated constructor stub
super(context);
paint = new Paint(Paint.ANTI_ALIAS_FLAG);
}
#Override
protected void onDraw(Canvas canvas) {
int screenWidth = canvas.getWidth();
int screenHeight = canvas.getHeight();
paint.setColor(Color.RED);
canvas.drawLine(0, 0, screenWidth, screenHeight, paint);
canvas.drawLine(factor*screenWidth, 0, factor*screenWidth, screenHeight, paint);
canvas.drawLine(0, factor*screenHeight, screenWidth, factor*screenHeight, paint);
invalidate();
}
}

1/2 is 0 (by integer division). Try 1f/2 or just 0.5f.

I think the problem is that 1/2 is integer division, and so 1/2 = 0. Try 0.5f instead.