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

这篇文章主要介绍了Android TextWatcher三个回调以及监听EditText的输入案例详解,本篇文章通过简要的案例,讲解了该项技术的了解与使用,以下就是详细内容,需要的朋友可以参考下

TextWatcher是一个监听字符变化的类。当我们调用EditText的addTextChangedListener(TextWatcher)方法之后，就可以监听EditText的输入了。
在new出一个TextWatcher之后，我们需要实现三个抽象方法：

beforeTextChanged
onTextChanged
afterTextChanged

看下beforeTextChanged的注释：

This method is called to notify you that, within s, the count characters beginning at start are about to be replaced by new text with length after. It is an error to attempt to make changes to s from this callback.

不知道你看懂没有，可能是因为英文水平的问题，我反正是看的很含糊不清。
既然这样，那最好的办法就是自己打个log试一下了。


    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);

首先输入abc123


    // 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);

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