Android EditText输入最大值提示功能

public class LengthFilter implements InputFilter {
public LengthFilter(int max) {
mMax = max;
}

@Override
public CharSequence filter(CharSequence source, int start, int end,
Spanned dest, int dstart, int dend) {
int keep = mMax - (dest.length() - (dend - dstart));

if (keep <= 0) {
if (mErrorToast == null) {
mErrorToast = Toast.makeText(ShowDetailCommentActivity.this, R.string.comment_input_overflow,
Toast.LENGTH_SHORT);
}
mErrorToast.show();
return "";
} else if (keep >= end - start) {
return null; // keep original
} else {
keep += start;
if (mErrorToast == null) {
mErrorToast = Toast.makeText(ShowDetailCommentActivity.this, R.string.comment_input_overflow,
Toast.LENGTH_SHORT);
}
mErrorToast.show();
if (Character.isHighSurrogate(source.charAt(keep - 1))) {
--keep;
if (keep == start) {
return "";
}
}
return source.subSequence(start, keep);
}
}

private int mMax;
}

mEditText.setFilters(new InputFilter[] { new LengthFilter(mMaxTextNum) });