和其他App分享文件（3）请求一个共享文件

这小节主要是展示一个客户端如何从一个服务端App请求一个文件，接收服务端App文件content URI，最后使用content URI 打开文件。

发送一个文件请求

客户端调用带有action为 ACTION_PICK 和客户端可以处理的MIME类型等的

Intent的startActivityForResult()方法。

例子如下：

public class MainActivity extends Activity {
private Intent mRequestFileIntent;
private ParcelFileDescriptor mInputPFD;
...
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mRequestFileIntent = new Intent(Intent.ACTION_PICK);
mRequestFileIntent.setType("image/jpg");
...
}
...
protected void requestFile() {
/**
* When the user requests a file, send an Intent to the
* server app.
* files.
*/
startActivityForResult(mRequestFileIntent, 0);
...
}
...
}

访问请求文件

下面的小片段代码展示的是客户端App如何处理服务端传递过来的Intent，并且客户端使用content URI 获得

FileDescriptor

/*
* When the Activity of the app that hosts files sets a result and calls
* finish(), this method is invoked. The returned Intent contains the
* content URI of a selected file. The result code indicates if the
* selection worked or not.
*/
@Override
public void onActivityResult(int requestCode, int resultCode,
Intent returnIntent) {
// If the selection didn't work
if (resultCode != RESULT_OK) {
// Exit without doing anything else
return;
} else {
// Get the file's content URI from the incoming Intent
Uri returnUri = returnIntent.getData();
/*
* Try to open the file for "read" access using the
* returned URI. If the file isn't found, write to the
* error log and return.
*/
try {
/*
* Get the content resolver instance for this context, and use it
* to get a ParcelFileDescriptor for the file.
*/
mInputPFD = getContentResolver().openFileDescriptor(returnUri, "r");
} catch (FileNotFoundException e) {
e.printStackTrace();
Log.e("MainActivity", "File not found.");
return;
}
// Get a regular file descriptor for the file
FileDescriptor fd = mInputPFD.getFileDescriptor();
...
}
}

openFileDescriptor() 烦hi一个文件的 ParcelFileDescriptor 对象。客户端通过这个对象得到 FileDescriptor

可以读取文件的对象。