How to programmatically set custom attributes of custom components?

Question

I have a custom component called CircleView, and I want to change a custom attribute called fillColor defined in attrs.xml:

<declare-styleable name="CircleView">
    <attr name="radius" format="integer" />
    <attr name="fillColor" format="color" />
</declare-styleable>

I have set it initially in my layout XML, which currently looks like this (namespace circleview is defined as xmlns:circleview="http://schemas.android.com/apk/res-auto"; it works fine when I define it in the XML, so this shouldn't be an issue):

<com.mz496.toolkit.CircleView
     ...
     circleview:fillColor="#33ffffff"/>

I can get the fillColor attribute just fine in my CircleView, which extends View, but I don't know how to set its value.

I've investigated things like setBackgroundColor and looked for other "set" methods, but I couldn't find any. I imagined a method like

circle.setAttribute(R.styleable.CircleView_fillColor, "#33ff0000")

Janis

You might also find answers here : #56561157 – Gerrygerrymander

Answer 1

A CircleView in the layout is nothing more than an instance of the CircleView class, so simply add a function into CircleView.java:

public void setFillColor(int newColor) {
    fillColor = newColor;
}

And then call it whenever needed:

CircleView circle_view = (CircleView) findViewById(R.id.circle_view);
circle_view.setFillColor(0x33ffffff);
circle_view.invalidate();

Also note that this just changes an internal variable, but you still need to redraw the custom component using the invalidate() method of the View class, since the custom component is only redrawn automatically if the entire view is redrawn, e.g. when switching fragments (see: Force a View to redraw itself).

(I figured this out at the very end when I was just about to ask, "Would I need to define this myself?" And I tried defining it myself, and it worked.)

Janis

Yeah, there's nothing in the stock Android tooling that automagically adds accessors corresponding to attributes, in part because that might not be the right answer for all use cases. I'm not aware of any third-party libraries that offer this, but I could certainly seem somebody rolling an annotation processor that tried to do this sort of code generation. – Apograph

Right, Android Studio silently tries to help by autocompleting method names (after typing public void set, it suggests set<member-variable-CamelCase-name>, but I think that's all that happens for now. – Janis

@Janis the above doesnt work for attribites defined in the xml – Warram