当方向改变android时保存活动状态

Question

I have an aacplayer app and I want to save the state of my activity when orientation changes from portrait to landscape. The TextViews do not appear to be empty, I tried to freeze my textview using this:

android:freezesText="true"

my manifest:

android:configChanges="orientation"

I also tried this:

@Override
    public void onConfigurationChanged(Configuration newConfig){
        super.onConfigurationChanged(newConfig);
        setContentView(R.layout.main2);

So when orientation changes to landscape I can see my layout-land main2.xml, that works but my textview goes out and appears empty. Streaming music works great. I can listen to it when orientation changes, but the text inside textviews are gone each time I change the orientation of my device.

What should I do to fix this so I can save the state?

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
....
....

Thank you very much.

Answer 1

When your orientation changes, you don't have to manually change to the landscape layout file. Android does this automatically for you. When orientation changes, Android destroys your current activity and creates a new activity again, this is why you are losing the text.

There are 2 parts you need to do, assuming you want a separate layout for portrait and landscape.

1. Assuming you have 2 XML layout files for portrait and landscape, put your main.xml layout file in the following folders:

   res/layout/main.xml <-- this will be your portrait layout
   res/layout-land/main.xml <-- this will be your landscape layout

   That's all you need to do, you don't have to touch the manifest file to modify android:configChanges="orientation" or override the onConfigurationChanged() . Actually, it's recommended you do not touch this for what you are trying to achieve.

2. Now to save your text from the text view =) Lets assume your textview is named as MyTextView in your layout xml file. Your activity will need the following:

    private TextView mTextView; private static final String KEY_TEXT_VALUE = "textValue"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); mTextView = (TextView) findViewById(R.id.main); if (savedInstanceState != null) { CharSequence savedText = savedInstanceState.getCharSequence(KEY_TEXT_VALUE); mTextView.setText(savedText); } } @Override protected void onSaveInstanceState (Bundle outState) { super.onSaveInstanceState(outState); outState.putCharSequence(KEY_TEXT_VALUE, mTextView.getText()); }

Basically, whenever Android destroys and recreates your Activity for orientation change, it calls onSaveInstanceState() before destroying and calls onCreate() after recreating. Whatever you save in the bundle in onSaveInstanceState, you can get back from the onCreate() parameter.

So you want to save the value of the text view in the onSaveInstanceState() , and read it and populate your textview in the onCreate(). If the activity is being created for the first time (not due to rotation change), the savedInstanceState will be null in onCreate() . You also probably don't need the android:freezesText="true"

You can also try saving other variables if you need to, since you'll lose all the variables you stored when the activity is destroyed and recreated.

Answer 2

static CharSequence savedText;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    if(savedText != null) {
        TextView mTextView = (TextView) findViewById(R.id.main);
        mTextView.setText(savedText);
    }
}

// Another function in activity, when you change text
public void actionButton(View view) {
    // Change and save text in textView
    savedText = "Change text";
    mTextView.setText(savedText);
}

Its work for me. But I think its not good code style and architecture for android.

Answer 3

There are two ways of doing this, the first one is in the AndroidManifest.xml file. You can add this to your activity's tag

android:configChanges="keyboardHidden|orientation|screenSize|screenLayout"

Or you can override two methods that will take care of this. This method requires some more effort, but arguably is much better. onSaveInstanceState saves the state of the activity before it's killed, and onRestoreInstanceState restores that information after onStart() Refer to the official documentation for a more in depth look.

In my sample code below, I am saving 2 int values, the current selection from the spinner as well as a radio button.

 @Override
    public void onSaveInstanceState(@NonNull Bundle savedInstanceState) {
        spinPosition = options.getSelectedItemPosition();
        savedInstanceState.putInt(Constants.KEY, spinPosition);
        savedInstanceState.putInt(Constants.KEY_RADIO, radioPosition);
        super.onSaveInstanceState(savedInstanceState);

    }

    // And I am restoring those values with `getInt`, then I can pass those stored values into the spinner and radio button group to select the same values that we saved earlier. 

    @Override
    public void onRestoreInstanceState(@NotNull Bundle savedInstanceState) {
        spinPosition = savedInstanceState.getInt(Constants.KEY);
        radioPosition = savedInstanceState.getInt(Constants.KEY_RADIO);
        options.setSelection(spinPosition, true);
        type.check(radioPosition);
        super.onRestoreInstanceState(savedInstanceState);
    }

Answer 4

I use in KOTLIN static var / val :

class MyFragment : Fragment()
{
     //all my code
     //access to static vars -> MyStaticClass.hello
}

class MyStaticClass 
{
    companion object {
        var hello: String = "Static text"
        var number_static: Int = 0
    }
}