How to draw directly to LinearLayout's canvas - Android - android-layout

Question

I have a LinearLayout with 3 ImageView s on it. Whenever the user clicks on an ImageView I want to draw a surrounding rectangle on the ImageView. I know how to draw something on a ImageView but I want to draw directly on the LinearLayout.
How can I do this?
I've already written the following code:
setContentView(R.id.anaekran2);
LinearLayout linLayout = (LinearLayout) findViewById(R.id.layout01);
Is there something like linLayout.getCanvas()?
I couldn't find a similiar function, but I've found
linLayout.getDrawingCache(). So,
Bitmap b = linLayout.getDrawingCache();
Canvas c = new Canvas(b); // this line gives an error, why?

Answer 1

You should create a custom linear layout. Overriding onDraw method of linear layout solves your problem. Here is the custom linear layout code.
public class CustomLinearLayout extends LinearLayout {
private Paint mPaint;
private int mClickedChild = -1;
public CustomLinearLayout(Context context) {
super(context);
setWillNotDraw(false);
createPaint();
}
public CustomLinearLayout(Context context, AttributeSet attrs) {
super(context, attrs);
setWillNotDraw(false);
createPaint();
}
public CustomLinearLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
setWillNotDraw(false);
createPaint();
}
#Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
super.onLayout(changed, l, t, r, b);
initializeChildrenClickEvent();
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
if(mClickedChild != -1){
View child = getChildAt(mClickedChild);
canvas.drawRect(child.getLeft(), child.getTop(), child.getRight(), child.getBottom(), mPaint);
}
}
private void initializeChildrenClickEvent(){
final int childCount = getChildCount();
OnClickListener clickListener = new OnClickListener() {
#Override
public void onClick(View view) {
for(int i = 0; i < childCount; i++){
if(getChildAt(i).equals(view)){
mClickedChild = i;
break;
}
}
invalidate();
}
};
for(int i = 0; i < childCount; i++){
getChildAt(i).setOnClickListener(clickListener);
}
}
private void createPaint(){
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setColor(Color.RED);
mPaint.setStrokeWidth(5f);
}
}
And here is the usage of custom layout in xml.
<CustomLinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:orientation="horizontal"
tools:context=".MainActivity">
<ImageView
android:id="#+id/image_view_1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:src="#drawable/ic_launcher" />
<ImageView
android:id="#+id/image_view_2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:src="#drawable/ic_launcher" />
<ImageView
android:id="#+id/image_view_3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:src="#drawable/ic_launcher" />
</CustomLinearLayout>