startActivityForResult

 1、 startActivityForResult（）和startActivity（）

startActivity()仅仅只是页面的跳转，如果想跳转回到原页面，还需要再使用一次startActivity().

 startActivityForResult（）可以直接完成上述任务，例如从A1 Activity跳转到A2 Activity，当A2 Activity调用了finish()方法以后，程序就会自动跳回A1 Activity并调用A1 Activity中的onActivityResult( )方法

2、主要函数

startActivityForResult(Intent intent, Int requestCode) A1
setResut(int resultCode, Intent intent) A2
onActivityResult(int requestCode, int resultCode, Intent intent) A1

A1 Activity中的startActivityForResult

toSecondButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent();
                intent.setClass(FirstActivity.this, SecondActivity.class);
                intent.putExtra("str", "I'm back");
                startActivityForResult(intent, BACK1);   //此处BACK1为1，也可以为其他值，但一定大于等于0

            }
        });

A1 Activity中重写onActivityResult方法（从A2返回后执行）

 @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        switch (requestCode){
            case BACK1:
                Bundle bundle=data.getExtras();
                String string=bundle.getString("back1");
                Toast.makeText(FirstActivity.this,string,Toast.LENGTH_SHORT).show();
                break;
            case BACK2 :
                Bundle bundle2=data.getExtras();
                String string2=bundle2.getString("back2");
                Toast.makeText(FirstActivity.this,string2,Toast.LENGTH_SHORT).show();
                break;
            case BACK3:
                Bundle bundle3=data.getExtras();
                String string3=bundle3.getString("ID");
                textView.setText(string3);
                Toast.makeText(FirstActivity.this,string3,Toast.LENGTH_SHORT).show();
                break;
            default:
                break;
        }
    }

A2 Activity中的setResut

        back1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent();
                intent.putExtra("back1","back button1");      //back button1"为传递的内容

                setResult(BACK1, intent);               //BACK1为resultcode
                intent.setClass(SecondActivity.this,FirstActivity.class);
                finish();                                //一定要有
            }
        });