一个小型加法计算器，在输入框里输入数据，键入button后进入下一个activity显示了计算结果，这时候按下返回键，输入过的数据还会输入框在里面。请问，如何在按返回的同时，清空原有文本框EditView中输入过的内容，让我在下一次输入的时候，输入框里是空白？

此段为第一个页面package dhu.qq.com;

import android.R.integer;

import android.app.Activity;

import android.content.Intent;

import android.os.Bundle;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.EditText;

import android.widget.TextView;

public class ZuoyeActivity extends Activity {

/** Called when the activity is first created. */

private EditText et1;

private EditText et2;

private Button bt1;

private Float f1, f2;

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

et1 = (EditText) findViewById(R.id.et1);

et2 = (EditText) findViewById(R.id.et2);

bt1 = (Button) findViewById(R.id.bt1);

bt1.setOnClickListener(new OnClickListener() {

@Override

public void onClick(View v) {

// TODO Auto-generated method stub

f1 = Float.parseFloat(et1.getText().toString());

f2 = Float.parseFloat(et2.getText().toString());

Bundle bd1 = new Bundle();

bd1.putFloat("iput1",f1);

bd1.putFloat("iput2",f2);

Intent itt1 = new Intent();

itt1.putExtra("transfer_bundle", bd1);

itt1.setClass(ZuoyeActivity.this, SecondyActivity.class);

startActivity(itt1);

}

});

}

}

此段为第二个页面/**

*

*/

package dhu.qq.com;

import java.security.PublicKey;

import android.R.string;

import android.app.Activity;

import android.content.Intent;

import android.os.Bundle;

import android.widget.TextView;

/**

* @author Administrator

*

*/

public class SecondyActivity extends Activity {

/*

* (non-Javadoc)

*

* @see android.app.Activity#onCreate(android.os.Bundle)

*/

private TextView tv21;

private Float f1, f2, f3;

private String str;

@Override

protected void onCreate(Bundle savedInstanceState) {

// TODO Auto-generated method stub

super.onCreate(savedInstanceState);

setContentView(R.layout.main2);

tv21 = (TextView) findViewById(R.id.tv21);

Intent itt2 = new Intent();

Bundle bd12 = new Bundle();

itt2 = this.getIntent();

bd12 = itt2.getBundleExtra("transfer_bundle");

f1 = bd12.getFloat("iput1");

f2 = bd12.getFloat("iput2");

f3 = f1 + f2;

str = String.valueOf(f3);

tv21.setText(str);

}

}

最终效果如图

零基础入门求教，谢谢各位大神！