布局中EditText在android布局中经常用到，对EditText中输入的内容也经常需要进行限制，我们可以通过TextWatcher去观察输入框中输入的内容，作个笔记。

主布局：

java代码：

package com.android.text;import android.app.Activity;import android.os.Bundle;import android.text.Editable;import android.text.TextWatcher;import android.util.Log;import android.widget.EditText;import android.widget.TextView;import android.widget.Toast;public class TextWatcherDemo extends Activity {    private TextView mTextView;    private EditText mEditText;    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        mTextView = (TextView)findViewById(R.id.tv);        mEditText = (EditText)findViewById(R.id.ET);        mEditText.addTextChangedListener(mTextWatcher);    }    TextWatcher mTextWatcher = new TextWatcher() {        private CharSequence temp;        private int editStart ;        private int editEnd ;        @Override        public void beforeTextChanged(CharSequence s, int arg1, int arg2,                int arg3) {            temp = s;        }               @Override        public void onTextChanged(CharSequence s, int arg1, int arg2,                int arg3) {            mTextView.setText(s);        }               @Override        public void afterTextChanged(Editable s) {            editStart = mEditText.getSelectionStart();            editEnd = mEditText.getSelectionEnd();            if (temp.length() > 10) {                Toast.makeText(TextWatcherDemo.this,                        "你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);            }        }    };}