接收Activity返回的结果
最后更新于:2022-04-01 01:37:56
> 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。