Casting between SpannableStringBuilder and CharSequence

Question

TextView tv = (TextView) findViewById(R.id.abc);
String rawString = "abcdefg";
SpannableStringBuilder ssb = new SpannableStringBuilder(rawString);
ssb.setSpan(new StyleSpan(android.graphics.Typeface.BOLD), 0, rawString.length(), Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
tv.setText(ssb);
CharSequence cs = tv.getText();
System.out.println(cs.getClass());

The output is "class android.text.SpannedString"

Why? I expect it to be "SpannableStringBuilder", my casting (SpannableStringBuilder ssb_2 = (SpannableStringBuilder)cs;) will give error for the example above.

Some more, the output will change to "SpannableString" if I set the buffer type of the text view to be android:bufferType="spannable"

Anyone know why?

Answer 1

1. Well the reason (SpannableStringBuilder ssb_2 = (SpannableStringBuilder)cs;) doesn't work is because SpannableStringBuilder implements CharSequence, meaning CharSequence does not know it can be casted to that. You can however do it the other way around. Does that make sense?

CharSequence is a nothing/itself

SpannableStringBuilder is a: CharSequence, Spannable, Editable, etc...

2. As for why android:bufferType="spannable" works, you are doing what I said above, the opposite. Since SpannableString implements CharSequence, it is now a child of it and therefore can be placed in CharSequence.

But anyways, the correct way to put your CharSequence in SpannableStringBuilder is by doing:

SpannableStringBuilder ssb_2 = SpannableStringBuilder(cs);

You might want to brush up on some polymorphism :) but you can see this in the Android docs on SpannableStringBuilder's constructor, or one of them at least.

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Update:

From what I notice on what you are doing, what is the need to use CharSequence? Just leave the TextView as is, meaning its returned as a String. So doing something like this would be easier:

SpannableStringBuilder ssb_2 = SpannableStringBuilder(tv.getText());

Reason that works is because String implements CharSequence as well, meaning that it as well can be passed into the SpannableStringBuilder constructor as a CharSequence. Java does automatic casting in certain cases, including in that code right above.