Saving state through the Bundle when you rotate the screen
Processing screen orientation changes in Android is one of the not yet automated tasks, developers need to manually save data, in some cases, change the markup and adapt the interface for tablets.
To begin with, let’s see where so many problems come from:
When the device orientation changes, the system terminates our activity and starts it again with the landscape version of the markup.
Accordingly, all the data displayed in the interface and the objects of our activity, as well as streaming processes (let’s talk about this in the second part of the article) are re-created.
Helping us not to become entangled in these seemingly simple-looking things will be helped by the already-implemented InstanceState method construction (onSave / onRestore) in the system.
1. Saving data
When creating any activity, your main method has a similar look:
protected void onCreate (Bundle savedInstanceState) {
super.onCreate (savedInstanceState);
setContentView (R.layout.activity_main);
}
The method signature already contains a savedInstanceState object of type Bundle and a call to a superclass.
In order to check how the default state saving works, let’s redefine the necessary methods:
@Override
protected void onRestoreInstanceState (Bundle savedInstanceState) {
super.onRestoreInstanceState (savedInstanceState);
}
@Override
protected void onSaveInstanceState (Bundle outState) {
super.onSaveInstanceState (outState);
}
Also, data recovery from forms is supported only for markup elements whose id is explicitly specified. Create an xml file, add a text field, a button and EditText to it:
<? xml version = “1.0” encoding = “utf-8”?>
<LinearLayout
xmlns: android = “http://schemas.android.com/apk/res/android"
xmlns: tools = “http://schemas.android.com/tools"
android: layout_width = “match_parent”
android: layout_height = “match_parent”
android: orientation = “vertical”
android: weightSum = “3”
android: padding = “10dp”
tools: context = “. MainActivity”>
<Textview
android: id = “@ + id / textView”
android: gravity = “center”
android: textSize = “20sp”
android: layout_weight = “1”
android: layout_width = “match_parent”
android: layout_height = “wrap_content”
android: text = “Hello World!” />
<Edittext
android: layout_width = “match_parent”
android: layout_height = “wrap_content”
android: ems = “10”
android: layout_marginTop = “10dp”
android: layout_marginBottom = “10dp”
android: layout_weight = “1”
android: inputType = “textPersonName”
android: text = “Example” />
<Button
android: id = “@ + id / button”
android: layout_weight = “1”
android: layout_width = “match_parent”
android: layout_height = “wrap_content”
android: text = “Button” />
</ LinearLayout>
By default, if you enter something in EditText and change the orientation of the device, the text will be saved, but this does not apply to the variables that we ourselves create in our activites. For example, add the function to increase the variable in our class by pressing the button
// counter variable
private int count;
@Override
protected void onCreate (Bundle savedInstanceState) {
super.onCreate (savedInstanceState);
setContentView (R.layout.activity_main);
// Set the click handler and call the counter method
Button btnCount = findViewById (R.id.button);
btnCount.setOnClickListener (new View.OnClickListener () {
@Override
public void onClick (View v) {
getCount ();
}
});
}
// Increment the variable by one and print its value.
private void getCount () {
++ count;
Toast.makeText (MainActivity.this, “Our count is” + count, Toast.LENGTH_SHORT) .show ();
}
@Override
protected void onRestoreInstanceState (Bundle savedInstanceState) {
super.onRestoreInstanceState (savedInstanceState);
}
@Override
protected void onSaveInstanceState (Bundle outState) {
super.onSaveInstanceState (outState);
}
}
Now, so that the value is saved when the screen is rotated, we need to edit the methods (onSave / onRestore) of the InstanceState as follows:
// Method of recovering values
@Override
protected void onRestoreInstanceState (Bundle savedInstanceState) {
super.onRestoreInstanceState (savedInstanceState);
// Restore our variable by key
count = savedInstanceState.getInt (“Count”);
// We can also set the default value after the key, separated by commas
}
// Save the variable before completing the activity
@Override
protected void onSaveInstanceState (Bundle outState) {
super.onSaveInstanceState (outState);
// Write the variable with the key in the Bundle
outState.putInt (“Count”, count);
}
Now we ourselves save the value of our variable and the user can rotate the device as he pleases, the information will still be saved and restored.
It is important, do not use the Bundle as a permanent repository for complex or large data, for this there is a SharedPerferences or database.
