c# - Xamarin ios：ABAddressbook.Create 始终为空，无法请求访问

Question

我在请求访问地址簿时遇到问题，因为 ABAddressbook.Create 始终为空。

那么如何请求访问权限？

NSError err = new NSError ();
ABAddressBook ab = ABAddressBook.Create(out err)
ab.RequestAccess (delegate {}); //ab always null

感谢帮助。

Answer 1

如果是这样，null那么你NSError应该告诉你它是什么（顺便说一句，不需要初始化out参数）。

一般来说（iOS6+）你的代码应该是这样的：

NSError err; 
var ab = ABAddressBook.Create (out err);
if (err != null) {
    // process error
    return;
}
// if the app was not authorized then we need to ask permission
if (ABAddressBook.GetAuthorizationStatus () != ABAuthorizationStatus.Authorized) { 
    ab.RequestAccess (delegate (bool granted, NSError error) { 
        if (error != null) {
            // process error
        } else if (granted) {
            // permission now granted -> use the address book
        } 
    }); 
} else { 
    // permission already granted -> use the address book
} 

Answer 2

这是我处理这种情况的公式。

private void RequestAddressBookAccess ()
{
    NSError error;
    ABAddressBook addressBook = ABAddressBook.Create (out error);
    if (error != null || addressBook == null)
        ShowAddressBookAccessInstructions ();

    else if (ABAddressBook.GetAuthorizationStatus () != ABAuthorizationStatus.Authorized) {
        addressBook.RequestAccess (delegate(bool granted, NSError err) {
            if (granted && err == null)
                this.InvokeOnMainThread (() => DoStuff (addressBook));
            else 
                ShowAddressBookAccessInstructions ();
        });
    } else
        DoStuff (addressBook);
}

private void ShowAddressBookAccessInstructions ()
{
    UIAlertView alert = new UIAlertView ("Cannot Access Contacts",
        "Go to Settings -> Privacy -> Contacts and allow this app to access your contacts to use this functionality",
        null, "Ok", null);
    alert.Show();
}