android TextView make invisible span on Kindle Fire

Question

I want to have a portion of my TextView invisible. In detail, I present a math problem to the user:

9 * 9 = 81

and I want 81 to be invisible. As user types correct answer, I make digit "8" and then "1" visible.

I tried to use TextAppearanceSpan and ForegroundColorSpan with transparent color (both #00000000 and Color.TRANSPARENT) and they work perfectly for every device and emulator except KindleFire device and emulator.

On Kindle Fire, "81" appears colored in sort-of-dark-grey. It seems that rasterizer tries to make it invisible against some "sort-of-dark-grey" background, not against background (which looks like grid paper image) that I've set in the root LinearLayout of my Activity.

enter image description here

My question is: how can I make a portion of text in TextView invisible using neither TextAppearanceSpan nor ForegroundColorSpan? Does there exist another "span" that measures text correctly, but does not paint it?

Update

I've discovered that there exist some mysterous RasterizerSpan and MetricAffectingSpan, which could (judging by the title) help.

As I can see, the only meaning of RasterizerSpan is to set a Rasterizer to the TextPaint object:

    public void updateDrawState(TextPaint ds) {
    ds.setRasterizer(mRasterizer);
}

I found it promising: if I were able to set a kind of "void" rasterizer (that just does nothing), it would make this text invisible. Unfortunately

new RasterizerSpan(null); // (set mRasterizer to null)

did not help.

My another idea is to implement a custom ShaderSpan that would set a "void" shader:

    public void updateDrawState(TextPaint ds) {
    ds.setShader(myCustomVoidShader);
}

but I do not understand how to create a shader that produces "nothing".

what happens on kindle fire if you set whole TextViews TextColor transparent? — Yalla T., Sep 27 '12 at 10:27
extend ForegroundColorSpan & override updateDrawState & do not call super method in that — Vishal Pawar, Sep 27 '12 at 10:43
>what happens on kindle fire if you set whole TextViews TextColor transparent it works fine (it is invisible). — Nick, Sep 27 '12 at 11:03
2Satya: super's method is ds.setColor(mColor). If I don't call it, color remains unchanged (=black). It will not be transparent. — Nick, Sep 27 '12 at 11:34

score 3 · Accepted Answer · answered Sep 27 '12 at 15:48

See if overriding updateDrawState() on your ForegroundColorSpan and calling setXferMode() will work:

public class TransparentSpan extends ForegroundColorSpan {
    private final PorterDuffXfermode MODE = new PorterDuffXfermode(PorterDuff.Mode.DST);

    public TransparentSpan(int color) {
        super(color);
    }

    @Override
    public void updateDrawState(TextPaint ds) {
        super.updateDrawState(ds);
        ds.setXfermode(MODE);
    }
}

Sorry, I didn't have a Kindle Fire to test with :)

score 1 · Answer 2 · answered May 20 '20 at 11:12

You can use AbsoluteSizeSpan, set the size to 0. So it will invisible

span = new AbsoluteSizeSpan(0, true); spannableString.setSpan(span, wordPosition.start, wordPosition.end, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);

Notice: The next word of the invisible word will take place the invisible word position.

score 0 · Answer 3 · answered Sep 27 '12 at 15:53

0

Why not using the android visibility (true or false). It will do the same job you need (or there is a specificreason you would lie to use Span) ?

answered Sep 27 '12 at 15:53

Milos Cuculovic

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android TextView make invisible span on Kindle Fire

3 Answers3