启动页：

btnButton.setOnClickListener(new OnClickListener() {

            @Override

            public void onClick(View v) {

                Intent intent = new Intent(MainActivity.this, SecondActivity.class);

                String str=txtEditText.getText().toString();

                intent.putExtra("fromMain", str);

                // startActivity(intent);

                // 启动需要监听返回值的Activity，并设置请求码：requestCode

                startActivityForResult(intent, 1);

            }

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
// 当otherActivity中返回数据的时候，会响应此方法
// requestCode和resultCode必须与请求startActivityForResult()和返回setResult()的时候传入的值一致。
if (requestCode == 1 && resultCode == SecondActivity.RESULT_CODE) {
Bundle bundle=data.getExtras();
String strResult = bundle.getString("result");
Log.i(TAG,"onActivityResult: "+ strResult);
Toast.makeText(MainActivity.this, strResult, Toast.LENGTH_LONG).show();
}
}

btnBack.setOnClickListener(new OnClickListener() {

            @Override

            public void onClick(View arg0) {

                Intent intent = new Intent();

                intent.putExtra("result", txtContent.getText().toString());

                setResult(RESULT_CODE, intent);// 设置resultCode，onActivityResult()中能获取到

                finish();

            }

        });