EditText设置监听，实现判断输入了多少个字符。

EditText提供了一个方法addTextChangedListener实现对输入文本的监控。在addTextChangedListener这个方法中，需要一个TextWatcher对象，在TextWatcher中提供了三个回调方法：(1)文本改变之前:beforTextChanged,(2)文本改变:onTextChanged,(3)文本改变之后:afterTextChange.

下面是起相关代码：布局文件相对比较简单，不在粘贴

package com.example.edittextchangeddemo;
import android.app.Activity;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {
private EditText ed_content;
private TextView tv_show;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tv_show = (TextView) findViewById(R.id.tv_show);
ed_content = (EditText) findViewById(R.id.ed_content);
ed_content.addTextChangedListener(new TextWatcher() {
private CharSequence temp;
private int editStart;
private int editEnd;

@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
temp = s;
}

@Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
// tv_show.setText(s);// 将输入的内容实时显示
}

@Override
public void afterTextChanged(Editable s) {
editStart = ed_content.getSelectionStart();
editEnd = ed_content.getSelectionEnd();
tv_show.setText("您输入了" + temp.length() + "个字符");
if (temp.length() > 10) {
s.delete(editStart - 1, editEnd);
int tempSelection = editStart;
ed_content.setText(s);
ed_content.setSelection(tempSelection);
Toast.makeText(MainActivity.this, "你输入的字数已经超过了！", Toast.LENGTH_SHORT).show();
}
}
});
}