限制EditText最多输入n位，设置EditText最大输入长度；

1、比较笨的方法：

/**
 * 设置edittext最大的输入限制
 * @param editText
 * @param length
 */
private void setMaxLength(EditText editText , int length){
    editText.addTextChangedListener(new TextWatcher() {
        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {

        }

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
            String str = s.toString();
            if (str.length()>length){
                editText.setText(str.substring(0,length)); //截取前x位
                editText.requestFocus();
                editText.setSelection(editText.getText().length()); //光标移动到最后
            }
        }

        @Override
        public void afterTextChanged(Editable s) {

        }
    });
}

如果重复设置，需要清空前一个；这是edittext的源码；

    /**
     * Adds a TextWatcher to the list of those whose methods are called
     * whenever this TextView's text changes.
     * <p>
     * In 1.0, the {@link TextWatcher#afterTextChanged} method was erroneously
     * not called after {@link #setText} calls.  Now, doing {@link #setText}
     * if there are any text changed listeners forces the buffer type to
     * Editable if it would not otherwise be and does call this method.
     */
    public void addTextChangedListener(TextWatcher watcher) {
        if (mListeners == null) {
            mListeners = new ArrayList<TextWatcher>();
        }

        mListeners.add(watcher);
    }

    /**
     * Removes the specified TextWatcher from the list of those whose
     * methods are called
     * whenever this TextView's text changes.
     */
    public void removeTextChangedListener(TextWatcher watcher) {
        if (mListeners != null) {
            int i = mListeners.indexOf(watcher);

            if (i >= 0) {
                mListeners.remove(i);
            }
        }
    }

2、简单实用：

 et.setFilters(new InputFilter[]{new NotChineseFilter(), new InputFilter.LengthFilter(4)}); //限制输入4位