Android入门之EditText（纯java）

import android.app.Activity;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.widget.*;

public class EditTextTest extends Activity {

private LinearLayout mainLayout=null;

private RelativeLayout layout=null;
private TextView tv1=null;		//标题
private TextView tv2=null;		//可输入剩余字符数
private EditText et=null;		//输入框

public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mainLayout_init();
setContentView(mainLayout);
}
/*mainLayout初始化*/
void mainLayout_init(){
mainLayout=new LinearLayout(this);
LinearLayout.LayoutParams lp=new LinearLayout.LayoutParams(-1, -1);
mainLayout.setLayoutParams(lp);
mainLayout.setOrientation(LinearLayout.VERTICAL);
layout_init();
mainLayout.addView(layout);
et_init();
mainLayout.addView(et);
}
/*layout1初始化*/
void layout_init(){
layout=new RelativeLayout(this);
RelativeLayout.LayoutParams lp=new RelativeLayout.LayoutParams(-1, -2);
layout.setLayoutParams(lp);
tv1_init();
layout.addView(tv1);
tv2_init();
layout.addView(tv2);
}
/*tv11初始化*/
void tv1_init(){
tv1=new TextView(this);
RelativeLayout.LayoutParams lp=new RelativeLayout.LayoutParams(-2, -2);
lp.addRule(RelativeLayout.ALIGN_PARENT_LEFT);
tv1.setLayoutParams(lp);
tv1.setTextSize(30);
tv1.setText("请输入账号:");
}
/*tv12初始化*/
void tv2_init(){
tv2=new TextView(this);
RelativeLayout.LayoutParams lp=new RelativeLayout.LayoutParams(-2, -2);
lp.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);
tv2.setLayoutParams(lp);
tv2.setTextSize(30);
tv2.setText("12");
}
/*et1初始化*/
void et_init(){
et=new EditText(this);
LinearLayout.LayoutParams lp=new LinearLayout.LayoutParams(-1,-2);
et.setLayoutParams(lp);
et.setSingleLine(true);
//字符变化监听
TextWatcher tw=new TextWatcher(){
public void afterTextChanged(Editable s) {
//限制输入，最多允许输入12个
if(et.length()>12){
//截取字符串，舍弃最后一个
et.setText((et.getText()).subSequence(0, 12));
//设置光标。由于用setText函数会导致光标复位，所以重新设置光标到末尾
et.setSelection(12);
}
//显示剩余可输入字符数
tv2.setText(String.valueOf(12-et.length()));
}
public void beforeTextChanged(CharSequence s, int start, int count,int after) {}
public void onTextChanged(CharSequence s, int start, int before,int count) {}
};
et.addTextChangedListener(tw);
}
}