Edittext设置过inputFilter后，再设置maxLength无效

原因

maxLength作为一个属性，也是用inputFilter实现的。如果自定义了inputFilter，就会覆盖掉原本maxLength的这个inputFilter，所以无效。

探究

EditText控件里没有maxLength这个属性
EditText继承TextView
TextView里有maxLength这个属性
设置maxLength的代码

if (maxlength >= 0) {
            setFilters(new InputFilter[] { new InputFilter.LengthFilter(maxlength) });
        } else {
            setFilters(NO_FILTERS);
        }

看看LengthFilter的代码

 public static class LengthFilter implements InputFilter {
        private final int mMax；`

        public LengthFilter(int max) {
            mMax = max;
        }


        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) {
                return "";
            } else if (keep >= end - start) {
                return null; // keep original
            } else {
                keep += start;
                if (Character.isHighSurrogate(source.charAt(keep - 1))) {
                    --keep;
                    if (keep == start) {
                        return "";
                    }
                }
                return source.subSequence(start, keep);
            }
        }

        /**
         * @return the maximum length enforced by this input filter
         */
        public int getMax() {
            return mMax;
        }
    }

int keep = mMax - (dest.length() - (dend - dstart));

这一行是计算还留有多少字符可以输入的
逻辑不复杂
**不过dend-dstart 我不明白，这两个值我测试在大部分情况下是一样的，删除字符情况下，dend-dstart = 1; **

参考的文章 http://blog.csdn.net/dw610/article/details/51586339