接收Activity返回的结果

> 编写:[kesenhoo](https://github.com/kesenhoo) - 原文:[http://developer.android.com/training/basics/intents/result.html](http://developer.android.com/training/basics/intents/result.html) 启动另外一个[activity](# "An activity represents a single screen with a user interface.")并不一定是单向的。我们也可以启动另外一个[activity](# "An activity represents a single screen with a user interface.")然后接受一个返回的result。为接受result，我们需要使用[startActivityForResult()](http://developer.android.com/reference/android/app/Activity.html#startActivityForResult(android.content.Intent, int)) ，而不是[startActivity()](http://developer.android.com/reference/android/app/Activity.html#startActivity(android.content.Intent))。 例如，我们的app可以启动一个camera程序并接受拍的照片作为result。或者可以启动联系人程序并获取其中联系的人的详情作为result。 当然，被启动的[activity](# "An activity represents a single screen with a user interface.")需要指定返回的result。它需要把这个result作为另外一个intent对象返回，我们的[activity](# "An activity represents a single screen with a user interface.")需要在[onActivityResult()](http://developer.android.com/reference/android/app/Activity.html#onActivityResult(int, int, android.content.Intent))的回调方法里面去接收result。 > **Note:**在执行`startActivityForResult()`时，可以使用explicit 或者 implicit 的intent。当启动另外一个位于的程序中的[activity](# "An activity represents a single screen with a user interface.")时，我们应该使用explicit intent来确保可以接收到期待的结果。 ### 启动[Activity](# "An activity represents a single screen with a user interface.") 对于startActivityForResult() 方法中的intent与之前介绍的并无太大差异，不过是需要在这个方法里面多添加一个int类型的参数。 该integer参数称为"request code"，用于标识请求。当我们接收到result Intent时，可从回调方法里面的参数去判断这个result是否是我们想要的。 例如，下面是一个启动[activity](# "An activity represents a single screen with a user interface.")来选择联系人的例子： ~~~ static final int PICK_CONTACT_REQUEST = 1; // The request code ... private void pickContact() { Intent pickContactIntent = new Intent(Intent.ACTION_PICK, Uri.parse("content://contacts")); pickContactIntent.setType(Phone.CONTENT_TYPE); // Show user only contacts w/ phone numbers startActivityForResult(pickContactIntent, PICK_CONTACT_REQUEST); } ~~~ ### 接收Result 当用户完成了启动之后[activity](# "An activity represents a single screen with a user interface.")操作之后，系统会调用我们[activity](# "An activity represents a single screen with a user interface.")中的onActivityResult() 回调方法。该方法有三个参数： - 通过startActivityForResult()传递的request code。 - 第二个[activity](# "An activity represents a single screen with a user interface.")指定的result code。如果操作成功则是`RESULT_OK` ，如果用户没有操作成功，而是直接点击回退或者其他什么原因，那么则是`RESULT_CANCELED` - 第它包含了返回的result数据的intent。 例如，下面显示了如何处理pick a contact的result： ~~~ @Override protected void onActivityResult(int requestCode, int resultCode, Intent data) { // Check which request we're responding to if (requestCode == PICK_CONTACT_REQUEST) { // Make sure the request was successful if (resultCode == RESULT_OK) { // The user picked a contact. // The Intent's data Uri identifies which contact was selected. // Do something with the contact here (bigger example below) } } } ~~~ 本例中被返回的Intent使用Uri的形式来表示返回的联系人。 为正确处理这些result，我们必须了解那些result intent的格式。对于自己程序里面的返回result是比较简单的。Apps都会有一些自己的api来指定特定的数据。例如，People app (Contacts app on some older versions) 总是返回一个URI来指定选择的contact，Camera app 则是在`data`数据区返回一个 Bitmap （see the class about [Capturing Photos](http://developer.android.com/training/camera/index.html)). ### 读取联系人数据 上面的代码展示了如何获取联系人的返回结果，但没有说清楚如何从结果中读取数据，因为这需要更多关于[content providers](http://developer.android.com/guide/topics/providers/content-providers.html)的知识。但如果想知道的话，下面是一段代码，展示如何从被选的联系人中读出电话号码。 ~~~ @Override protected void onActivityResult(int requestCode, int resultCode, Intent data) { // Check which request it is that we're responding to if (requestCode == PICK_CONTACT_REQUEST) { // Make sure the request was successful if (resultCode == RESULT_OK) { // Get the URI that points to the selected contact Uri contactUri = data.getData(); // We only need the NUMBER column, because there will be only one row in the result String[] projection = {Phone.NUMBER}; // Perform the query on the contact to get the NUMBER column // We don't need a selection or sort order (there's only one result for the given URI) // CAUTION: The query() method should be called from a separate thread to avoid blocking // your app's UI thread. (For simplicity of the sample, this code doesn't do that.) // Consider using CursorLoader to perform the query. Cursor cursor = getContentResolver() .query(contactUri, projection, null, null, null); cursor.moveToFirst(); // Retrieve the phone number from the NUMBER column int column = cursor.getColumnIndex(Phone.NUMBER); String number = cursor.getString(column); // Do something with the phone number... } } } ~~~ > **Note**:在Android 2.3 (API level 9)之前对`Contacts Provider`的请求(比如上面的代码)，需要声明`READ_CONTACTS`权限(更多详见[Security and Permissions](http://developer.android.com/guide/topics/security/security.html))。但如果是Android 2.3以上的系统就不需要这么做。但这种临时权限也仅限于特定的请求，所以仍无法获取除返回的Intent以外的联系人信息，除非声明了`READ_CONTACTS`权限。