Android完美实现EditText换行自动缩进
package club.andnext.text;
import android.text.Editable;
import android.text.TextUtils;
import android.text.TextWatcher;
public class IndentTextWatcher implements TextWatcher {
int markStart = -1;
int changeCount = -1;
@Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
this.markStart = -1;
this.changeCount = -1;
}
@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
this.markStart = start;
this.changeCount = count;
}
@Override
public void afterTextChanged(Editable s) {
int start = this.markStart;
int count = this.changeCount;
if (count == 1 && s.charAt(start) == '\n') {
indent(s, start);
}
this.markStart = -1;
this.changeCount = -1;
}
static void indent(Editable s, int start) {
CharSequence value = getIndent(s, start);
if (!TextUtils.isEmpty(value)) {
s.insert(start + 1, value);
}
}
static CharSequence getIndent(Editable s, int start) {
int begin = lastIndexOf(s, '\n', start - 1);
begin = (begin < 0)? 0: (begin + 1);
int end = begin;
for (int i = begin, length = start + 1; i < length; i++) {
char c = s.charAt(i);
if (!isWhitespace(c)) {
end = i;
break;
}
}
if (end > begin) {
return s.subSequence(begin, end).toString();
}
return null;
}
static boolean isWhitespace(char c) {
return (c == ' ')
|| (c == '\t')
|| (c == '\u3000');
}
private static int lastIndexOf(Editable s, char ch, int fromIndex) {
if (ch < Character.MIN_SUPPLEMENTARY_CODE_POINT) {
// handle most cases here (ch is a BMP code point or a
// negative value (invalid code point))
int i = Math.min(fromIndex, s.length() - 1);
for (; i >= 0; i--) {
if (s.charAt(i) == ch) {
return i;
}
}
return -1;
} else {
return lastIndexOfSupplementary(s, ch, fromIndex);
}
}
private static int lastIndexOfSupplementary(Editable s, int ch, int fromIndex) {
if (Character.isValidCodePoint(ch)) {
char hi = Character.highSurrogate(ch);
char lo = Character.lowSurrogate(ch);
int i = Math.min(fromIndex, s.length() - 2);
for (; i >= 0; i--) {
if (s.charAt(i) == hi && s.charAt(i + 1) == lo) {
return i;
}
}
}
return -1;
}
}