Android: Enable Scrollbars on Canvas-Based View

Question

I have a custom view that extends View. It displays drawn shapes, and allows the user to add to those drawings via drawing touch events to the View via onDraw.

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Answer 1

If you are creating your custom view programatically, then the answer is the following: in order to show scrollbars on custom view class, the method "initializeScrollbars" should be called during initialization (in constructor for example).

This method takes one very obscure parameter of type TypedArray. To get suitable TypedArray instance you need to create custom styleable entry - just create file "attrs.xml" in your "res\values" directory with the following content:

Also the complete scrollbars initialization code is (place it on your custom view constructor):

setHorizontalScrollBarEnabled(true);
setVerticalScrollBarEnabled(true);

TypedArray a = context.obtainStyledAttributes(R.styleable.View);
initializeScrollbars(a);
a.recycle();

P.S. the solution was tested on Android 2.0

I have forgot to add: also "computeVerticalScrollRange" and "computeHorizontalScrollRange" methods should be overridden. They should just return imaginary width and height of the canvas.