Android development Activity status save OnSaveInstanceState Parameter Parsing, saveinstancestate

Android development Activity status save OnSaveInstanceState Parameter Parsing, saveinstancestate

Author:Han shuliang

Repost the famous source: Http://blog.csdn.net/shulianghan/article/details/38297083

1. Related Methods

1. Example of saving status

package com.example.octopus_saveinstance;import android.app.Activity;import android.os.Bundle;public class MainActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);}@Overrideprotected void onRestoreInstanceState(Bundle savedInstanceState) {super.onRestoreInstanceState(savedInstanceState);}@Overrideprotected void onSaveInstanceState(Bundle outState) {super.onSaveInstanceState(outState);}}

2. Related Methods

(1) onCreate (Bundle savedInstanceState) Method

Callback when Activity is created: This method will automatically pass in a Bundle object, which is the data stored in onSaveInstanceState or onRestoreInstanceState during the last destruction by the system;

--Note:: The Bundle object data is saved only when the system automatically recycles the data;

--Bundle object Source: The Bundle object parameter in the onCreate () method is the Bundle object saved in the onSaveInstance () or onRestoreInstanceState () method;

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(2) onSaveInstanceState (Bundle outState) Method

Role of the outState Parameter:

--Data Storage: When the Activity declares that the Activity state needs to be saved at the end of the cycle, the data to be saved is saved in the Bundle object in the form of a key-value pair;

--Restore data: A Bundle object is passed in when the onCreate () method of the Activity creates the Activity. This Bundle object is the outState parameter;

Call time: Called when the Activity is easily destroyed. Note that the Activity is easily destroyed or called if it is not destroyed;

--Press the Home Key.: This method is called when Activity enters the background;

--Press power: The screen is closed. The Activity enters the background;

--Start other activities: The Activity is pushed to the stack bottom of the task stack;

--Horizontal/vertical screen Switching: Destroys the current Activity and creates it again;

Considerations for calling the onSaveInstanceState Method:

--The user actively destroys the data and does not call the data.: This method is not called when you click the rollback key or call the finish () method;

--The call time is not fixed.: This method must be called before the onStop () method, but it is not sure whether it is called before or after the onPause () method;

--Component status storage in Layout: Each component implements the onSaveInstance () method. When calling a function, the status of the component is automatically saved. Note that only the component with an id is saved;

--About the default super. onSaveInstanceState (outState): The default method is to save the component status;

(3) onRestoreInstanceState (Bundle savedInstanceState) Method

Method callback time: After the Activity is destroyed by the SystemRestore ActivityCalled. It is called only when the Activity is destroyed and rebuilt. If the memory is sufficient and the system does not destroy the Activity, you do not need to call it;

--Bundle object transfer: The Bundle object stored in this method will also be passed to the onCreate () method through parameters when the Activity is restored;

--In the lifecycle: This method saves information before the onResume () method;

Sample Code

Activity Code:

package com.example.octopus_saveinstance;import android.app.Activity;import android.os.Bundle;public class MainActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);if(savedInstanceState != null)System.out.println("onCreate() : " + savedInstanceState.getString("octopus"));}@Overrideprotected void onRestoreInstanceState(Bundle savedInstanceState) {super.onRestoreInstanceState(savedInstanceState);System.out.println("onRestoreInstanceState() : " + savedInstanceState.getString("octopus"));}@Overrideprotected void onSaveInstanceState(Bundle outState) {super.onSaveInstanceState(outState);outState.putString("octopus", "www.octopus.org.cn");System.out.println("onSaveInstanceState() : save date www.octopus.org.cn");}}

Running result: Rotate the screen during running;

I/System.out( 8167): onSaveInstanceState() : save date www.octopus.org.cnI/System.out( 8167): onCreate() : www.octopus.org.cnI/System.out( 8167): onRestoreInstanceState() : www.octopus.org.cn

Author:Han shuliang

Repost the famous source: Http://blog.csdn.net/shulianghan/article/details/38297083

Android development and activity storage status issues

You can reload the keyboard response in B to filter out the backkey. In this way, the system cannot return to. Of course, it can also be tricky. You can use the original method, but you can store the data in a local database or file before you finish. Read it in onResume. These are two ideas. I hope the landlord will adopt it. Thank you.

An android example calls the data storage function in both onSaveInstanceState and onPause. Why?

Save it in onPause. An activity must go through onPause as long as it is in the background or destroyed.