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Android Activity Lifecycle

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Saving and Retrieving Data with SharedPreferences

4:24 with Ben Deitch

What good are SharedPreferences if we don't use them? In this video we'll see how to save and retrieve the data we store in SharedPreferences as well as briefly touch on a couple of other important methods.

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    Now that we have our editor we can start saving our values. 0:00
    We learned in a previous video that the on pause life cycle method 0:04
    is a good place to save any unsaved changes. 0:07
    Let's make some space at the bottom of our file and 0:11
    use the Ctrl+O shortcut to override the on pause method. 0:14
    Then, we can store our string using the putString method of our editor. 0:23
    It takes two parameters, the key and the value. 0:28
    Let's type mEditor.putString and 0:32
    I'll call my key KEY_EDITTEXT. 0:39
    And for the value, we'll do mEditText.getText, 0:45
    which returns an editable. 0:51
    Then .toString, to make it a string. 0:54
    Then we can use Alt+Enter on the key to create it. 1:02
    I'll name mine similar to the variable, key_edittext. 1:09
    Now that we've saved our string to the editor, 1:16
    we just need to add mEditor.apply 1:19
    to save our changes to our shared preferences object. 1:24
    We've now saved the value of our edit text in the on pause method. 1:31
    All that's left is to retrieve that value in the on create method and 1:35
    set the text of our edit text to that value. 1:40
    We can retrieve the value by using the get string method 1:44
    on a shared preference object. 1:47
    When retrieving a value from a shared preference we need to provide the key for 1:50
    the value and a default value to use in case that key isn't found. 1:54
    In the bottom of our on create, let's retrieve our string by calling 2:00
    MSharedPreferences.getString and 2:05
    passing in our KEY_EDITTEXT string for 2:13
    the key parameter and an empty string for the default value. 2:17
    Next, let's save this value into a string called editTextString. 2:24
    Lastly, let's update our edit text by typing mEditText.setText. 2:37
    And we'll set it to editTextString. 2:48
    The last step is to test the app to make sure it works as expected. 2:53
    I'll type in some text. 3:00
    And close the app by hitting the back button. 3:07
    And when we reopen the app, our text is still here, perfect. 3:20
    Before we go on, let's talk about removing shared preference values. 3:25
    This is especially useful for 3:31
    testing, or if your users want to reset an app to it's default values. 3:32
    This can be done by using the clear method of a shared preference editor object. 3:38
    Also, we can use the remove method, and pass in a key, to remove just one value. 3:43
    Once you're done removing values, 3:51
    don't forget to use the apply method to save your changes. 3:53
    Shared preferences is the easiest way to store data in Android, but 3:57
    only if that data can easily fit into a key value pair. 4:01
    If you're interested in how to store more complicated data, like a picture or 4:05
    a Java file, please check out our videos on data persistence in Android, 4:08
    which are linked in the teacher's notes. 4:13
    They also cover shared preferences in a little more detail. 4:15
    For now, we're going to move onto a practice project 4:18
    to test everything that you've learned so far. 4:21

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