TextWatcher提供了3个回调方法：

1.文本改变前：beforeTextChanged

2.文本改变：onTextChanged

3.文本改变之后：afterTextChanged

布局文件：

android:layout_width="fill_parent"

android:layout_height="fill_parent"

android:orientation="vertical">

android:id="@+id/tv"

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:ellipsize="marquee"

android:focusable="true"

android:focusableInTouchMode="true"

android:marqueeRepeatLimit="marquee_forever"

android:scrollHorizontally="true"

android:text="输入的结果为:" />

android:id="@+id/et"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:hint="请输入:"/>

主类：

public class MainActivity extends AppCompatActivity {

private TextView mTextView;

private EditText mEditText;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

mTextView = (TextView) findViewById(R.id.tv);

mEditText = (EditText) findViewById(R.id.et);

/**

* 监听EditText框中的变化

*/

mEditText.addTextChangedListener(new TextWatcher() {

private CharSequence temp;

private int editStart;

private int editEnd;

/**

* 文本变化之前

* @param s

* @param start

* @param count

* @param after

*/

@Override

public void beforeTextChanged(CharSequence s, int start, int count, int after) {

temp = s;

}

/**

* 文本变化中

* @param s

* @param start

* @param before

* @param count

*/

@Override

public void onTextChanged(CharSequence s, int start, int before, int count) {

mTextView.setText("输入的结果为:"+s);

}

/**

* 文本变化之后

* @param s

*/

@Override

public void afterTextChanged(Editable s) {

editStart = mEditText.getSelectionStart();

editEnd = mEditText.getSelectionEnd();

if (temp.length() > 10) {//限制长度

Toast.makeText(MainActivity.this,

"输入的字数已经超过了限制！", Toast.LENGTH_SHORT)

.show();

s.delete(editStart - 1, editEnd);

int tempSelection = editStart;

mEditText.setText(s);

mEditText.setSelection(tempSelection);

}

}

});

}

}

结果：

(责任编辑：最模板)