How To Change A View From A Different Activity.

Right now my goal is to have the Colors activity allow users to hit a button to change the color they are drawing with. How do I get the instance of the canvas in my activity_main.

Solution 1:

My understanding is that, you want to change the color of DrawingView view on any event (ex: button click).

For that please follow the below code :

Firstly, create the attribute styles in attrs.xml

<declare-styleable name="DrawingView">

    <!-- drawing view color attributes -->
    <attr name="dv_background_color" format="color" />
    <attr name="dv_foreground_color" format="color" />

    <!-- You can add other custom attributes also -->
    <attr name="dv_padding" format="dimension" />
    <attr name="dv_width" format="dimension" />
</declare-styleable>

Now write the below code in your java class file :

public class DrawingView extends View {

 //Default colors
 private int mDrawingViewBackgroundColor = 0xFF0000FF;
 private int mDrawingViewForegroundColor = 0xFF0000FF;

 //Default padding
 private int mViewPadding = 5;
 private int mViewWidth = 10;

private Paint mForeGroundColorPaint = new Paint();
private Path mBackGroundColorPaint = new Path();

public DrawingView(Context context, AttributeSet attrs) {
    super(context, attrs);

    TypedArray typeArr = context.obtainStyledAttributes(attrs, R.styleable.DrawingView);
  try {

    //Inflate all the attributes of DrawingView from xml that are initialize in activity_main.xml layout file.
    mDrawingViewBackgroundColor = typeArr.getColor(R.styleable.DrawingView_dv_background_color, mDrawingViewBackgroundColor);
    mDrawingViewForegroundColor = (R.styleable.DrawingView_dv_background_color, mDrawingViewForegroundColor);

    mViewPadding = (int)typeArr.getDimension(R.styleable.DrawingView_dv_padding, mViewPadding);

    mViewWidth = (int)typeArr.getDimension(R.styleable.DrawingView_dv_width, mViewWidth);
   }finally {
        typeArr.recycle();
    }

    setupPaints();
}

setupPaints() {
   //Render DrawingView colors - Foreground color
   mForeGroundColorPaint.setColor(mDrawingViewForegroundColor);
   mForeGroundColorPaint.setAntiAlias(true);
   mForeGroundColorPaint.setStrokeWidth(5f);
   mForeGroundColorPaint.setStyle(Paint.Style.STROKE);
   mForeGroundColorPaint.setStrokeJoin(Paint.Join.ROUND);

   //Render DrawingView colors - Background color
   mBackGroundColorPaint.setColor(mDrawingViewBackgroundColor);
   mBackGroundColorPaint.setAntiAlias(true);
   mBackGroundColorPaint.setStrokeWidth(5f);
   mBackGroundColorPaint.setStyle(Paint.Style.STROKE);
   mBackGroundColorPaint.setStrokeJoin(Paint.Join.ROUND);
}

@Override
public void invalidate() {
    setupPaints();
    super.invalidate();
}

@Override
protected void onDraw(Canvas canvas) {
    canvas.drawPath(path, paint);
}

}