Android ApiDemos示例解析(11)：App->Activity->Receive Result

startActivity可以启动一个新的Activity，这个新的Activity与启动它Activity之间相对独立，不会返回给调用它的Activity如何结果。在写应用时，有时需要从其它Activity返回结果。Receive Result显示了这个用法。
startActivityForResult 使用方法和startActivity类似，重要的是startActivityForResult可以从被调用的Activity返回结果。GET_CODE为Request code，当子Activity返回结果时可以根据这个Request Code来处理Activity返回的结果。

// Definition of the one requestCode we use for receiving resuls.static final private int GET_CODE = 0; private OnClickListener mGetListener = new OnClickListener() {    public void onClick(View v) {        // Start the activity whose result we want to retrieve.  The        // result will come back with request code GET_CODE.        Intent intent = new Intent(ReceiveResult.this, SendResult.class);        startActivityForResult(intent, GET_CODE);    }};

当子Activity结束时，调用setResult 来设置返回结果。Receive Result例子中涉及了两个Activity， ReceiveResult为父Activity，SendResult为子Activity返回用户选项，返回的结果在ReceiveResult中显示。
SendResult 返回结果的代码如下：

private OnClickListener mCorkyListener = new OnClickListener(){    public void onClick(View v)    {        // To send a result, simply call setResult() before your        // activity is finished.        setResult(RESULT_OK, (new Intent()).setAction("Corky!"));        finish();    }}; private OnClickListener mVioletListener = new OnClickListener(){    public void onClick(View v)    {        // To send a result, simply call setResult() before your        // activity is finished.        setResult(RESULT_OK, (new Intent()).setAction("Violet!"));        finish();    }};

当从子Activity返回结果后，父Activity通过定义onActivityResult来处理子Activity返回的结果。

protected void onActivityResult(int requestCode, int resultCode,        Intent data) {        // You can use the requestCode to select between multiple child        // activities you may have started.  Here there is only one thing        // we launch.        if (requestCode == GET_CODE) {             // We will be adding to our text.           ...        }    }

onActivityResult中的三个参数:
requestCode: 就是在调用startActivityForResult 时的request code,可以使用request code 来区分多个子Acitivity。
resultCode：为子Activity的返回值，一般为RESULT_OK (正常）,RESULT_CANCELLED(取消）。
Data: Activity的返回结果。例子中为用户选择的Corky或是Violet。