Android EditText java 设置 maxLength

我们在开发过程，经常会遇到EditText 设置可输入内容长度，但是发现java代码没有set方法，通过源码，我们发现InputFilter的妙用所在。

在TextView中我们发现maxLength默认值为-1，并且当mxLength大于等于0才会设置LengthFilter

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

接下来，我们查看一下 InputFilter.LengthFilter 中代码

/**
     * This filter will constrain edits not to make the length of the text
     * greater than the specified length.
     */
    public static class LengthFilter implements InputFilter {
        @UnsupportedAppUsage
        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;
        }
    }

那么我们EditText可以：

editText.setFilters(new InputFilter[] { new InputFilter.LengthFilter(maxlength) });来实现，java代码设置 最大输入内容长度。

InputFilter可以实现很多功能。