Android TextWatcher三个回调以及监听EditText的输入案例详解

    EditText et = (EditText) findViewById(R.id.et);
    TextWatcher watcher = new TextWatcher() {
        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {
            Log.d(TAG, "beforeTextChanged: s = " + s + ", start = " + start +
                    ", count = " + count + ", after = " + after);
        }

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
            Log.d(TAG, "onTextChanged: s = " + s + ", start = " + start +
                    ", before = " + before + ", count = " + count);
        }

        @Override
        public void afterTextChanged(Editable s) {
            Log.d(TAG, "afterTextChanged: " + s);
        }
    };
    et.addTextChangedListener(watcher);

    // 用于屏蔽空格输入的TextWatcher
    TextWatcher watcher = new TextWatcher() {
        private String mBefore;// 用于记录变化前的文字
        private int mCursor;// 用于记录变化时光标的位置

        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {
            mBefore = s.toString();
            mCursor = start;
            Log.d(TAG, "beforeTextChanged: " + s + ", " + mCursor);
        }

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
            Log.d(TAG, "onTextChanged: " + s);
        }

        @Override
        public void afterTextChanged(Editable s) {
            Log.d(TAG, "afterTextChanged: " + s);
            // 这里图方便，是在afterTextChanged判断是否输入之后含有空格，并不是最好的方案
            // 理论上应该在onTextChanged中判断输入内容
            if (s.toString().contains(" ")) {
                Log.i(TAG, "onTextChanged: 包含空格, 设置" + mBefore);
                et.removeTextChangedListener(this);
                et.setText(mBefore);
                et.addTextChangedListener(this);
                et.setSelection(mCursor);
            }
        }
    };
    et.addTextChangedListener(watcher);