Develop Reference

Draw a line in Android without setting it as content

Just a newbie here.
Is it possible to draw a line over a layout?
I have an XML file(activity_main) and it contains a layout which is ImageLayout that I took from github. The layout contains an image and several buttons.
What I want to do is to draw a line between two points on the layout. In order to draw a line, people usually create a Draw class and extends View. On the MainActivity, they would setContent the Draw class. I have already setContent my XML file. How would I draw a line from this point?
EDIT:
I heard about the class Path, I think it is better than using onDraw because I would be connecting(drawing lines between) several points in my layout.
Enlighten me about it if you could

Subclass the container ViewGroup and override its dispatchDraw() method. I am providing example of subclassed LinearLayout, however, this would work with any other ViewGroup.
public class MyLinearLayout extends LinearLayout {
private Paint paint;
public MyLinearLayout(Context context) {
super(context);
initPaint();
}
public MyLinearLayout(Context context, AttributeSet attrs) {
super(context, attrs);
initPaint();
}
public MyLinearLayout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
initPaint();
}
private void initPaint() {
paint = new Paint();
paint.setColor(Color.RED);
paint.setStrokeWidth(10);
}
#Override
protected void dispatchDraw(Canvas canvas) {
super.dispatchDraw(canvas);
canvas.drawLine(0, 0, canvas.getWidth(), canvas.getHeight(), paint);
}
}

Use this in your layout to do an horizontal line:
android:layout_width="fill_parent"
android:layout_height="2dp"
android:background="#c0c0c0"/>

Custom EditText with rectangle drawn around it not compatible with gravity

I am trying to create a custom EditText class with a rectangle drawn around it. I got that to work rather easily. But then I also wanted the text to be centered and therefore I set gravity = center. However that made the rectangle around the box disappear. Is the gravity property changing the bounding box? How can I retrieve the correct bounding box?
The class is as follows:
public static class LetterBox extends EditText {
private Paint mPaint = new Paint();
public LetterBox(Context context) {
super(context);
this.setupPaint();
}
public LetterBox(Context context, AttributeSet attrs) {
super(context,attrs);
this.setupPaint();
super.setGravity(Gravity.CENTER);
}
public LetterBox(Context context, AttributeSet attrs, int defStyle) {
super(context,attrs,defStyle);
this.setupPaint();
super.setGravity(Gravity.CENTER);
}
#Override
protected void onDraw(Canvas canvas) {
canvas.drawRect(0,0,getMeasuredWidth()-1,getMeasuredHeight()-1,mPaint);
super.onDraw(canvas);
}
private void setupPaint() {
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setColor(Color.BLACK);
}
}

I have implemented your code and it is working as expected. The only thing I had to change was remove the static modifier from the class. Did you intend to use static?

Extended LinearLayout not rotating

I'm trying to create a custom LinearLayout that can rotate all children in the layout by a set angle. That is, I want to rotate the entire canvas and the children, not the children individually.
I need to support API Level 10, so android:rotate which was introduced in API Level 11 will not help me here.
I've been looking around and think I need to do something along the lines of this code below, but with this code nothing gets rotated.
Any ideas on what I'm missing here?
public class RotationLayout extends LinearLayout {
public RotationLayout(Context context) {
super(context);
init();
}
public RotationLayout(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public RotationLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init();
}
private void init() {
setWillNotDraw(false);
}
#Override
protected void onDraw(Canvas canvas) {
canvas.save();
canvas.rotate(350,0,0);
super.onDraw(canvas);
canvas.restore();
}
}`

I tried your code with a few changes.
In the onCreate(Bundle) of an activity class, I initialized the RotationLayout:
RotationLayout rl = new RotationLayout(this);
ImageView iv = new ImageView(this);
iv.setImageDrawable(getResources().getDrawable(R.drawable.some_drawable));
rl.addView(iv);
setContentView(rl);
And the view was indeed rotated 350 degrees(or 10 degrees counter-clockwise) around (0,0). This was what I changed:
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.rotate(350,0,0);
}
From notes on Canvas.save() (Link):
Saves the current matrix and clip onto a private stack. Subsequent
calls to translate,scale,rotate,skew,concat or clipRect,clipPath will
all operate as usual, but when the balancing call to restore() is
made, those calls will be forgotten, and the settings that existed
before the save() will be reinstated.

Android canvas issue

I am new to android. Now I generated two ImageView in my Android XML file. I want to use canvas to draw two circles in each view. But the problem is, how can I deal with the coordinates? How can I know the coordinates? And how can I center them? Thanks!

ImageViews are for displaying image files, normally. If you want to draw your view yourself, you create your own View and override the onDraw method. Here is a class that draws a big red circle inside itself:
public class CircleView extends View {
public CircleView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
public CircleView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public CircleView(Context context) {
super(context);
}
#Override
protected void onDraw(Canvas canvas) {
Paint red = new Paint();
red.setColor(0xffff0000);
int height = getHeight();
int width = getWidth();
int radius = width < height ? width/2 : height/2;
canvas.drawCircle(width/2, height/2, radius, red);
}
}

You cannnot draw cirlces in an ImageView. You can only draw a circle in a bitmap and apply that bitmap to an ImageView.
Or you can create custom views and draw directly on their canvas.
In both cases you need to find the size of these views after they are created. Then you will know the coordinates as the 0,0 starts in the top left corner.

How can I add a decorator image on top of my image view

I have an ImageView in my android layout. And I would like to add a 'decorator' image at the lower right corner of my image view.
Can you tell me how can I do it?
I am thinking of doing with a FramLayout with 2 image views as its child, but how can i make one image the lower right corner of another?
<FrameLayout>
<ImageView .../>
<ImageView .../>
</FrameLayout>

You probably want to be using a RelativeLayout (Documentation) instead - it supports stacking views, and all you'd have to do is align the bottom and left of the overlay ImageView with the bottom and left.

You could create your own class that extends ImageView. It will always draw decorator over the ImageView content.
public class MyImage extends ImageView {
static Bitmap decorator;
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
if(decorator==null)
decorator = BitmapFactory.decodeResource(getResources(), R.drawable.decorator);
canvas.drawBitmap(decorator, 0, 0, null);
}
public MyImage(Context context) {
super(context);
}
public MyImage(Context context, AttributeSet attrs) {
super(context, attrs, 0);
}
public MyImage(Context context, AttributeSet attrs, int params) {
super(context, attrs, params);
}
}