Android：如何在后退按钮操作栏和设备的后退按钮上保留对象的状态

Question

I have ActivityA and ActivityB. ActivityB is called from ActivityA.

I wanted to retain the object of ActivityA, when I press back button of ActionBar or back button of device.

I have created a Singleton object to save my object and to get my object.

onPause() I am saving the object and onResume() method I am getting the object.

My problem here is the behaviour is different, the object that I get when back button of Action (in ActivityB) is different from the object that I get when back button of back button is clicked.

Here is the code:

protected void onPause() {
    //resetSort();
    super.onPause();
    MySingleton.getInstance().setMyObject(myObject);
}

@Override
protected void onResume() {
    super.onResume();
    myObject = MySingleton.getInstance().getMyObject();
}

Here is my manifest file.

    <activity
        android:name=".ActivityA"
        android:configChanges="orientation|keyboardHidden|screenSize"
        android:label="@string/app_name"
        >
    </activity>
    <activity
        android:name=".ActivityB"
        android:configChanges="orientation|keyboardHidden|screenSize"
        android:label="@string/app_name" >
    </activity>

Code from ActivityB:

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case android.R.id.home:
            NavUtils.navigateUpFromSameTask(this);
            return true;
    }
    return super.onOptionsItemSelected(item);
}

Any solution is appreciated. Thanks

Answer 1

The most reliable way is to use SharedPreferences . It's both thread safe and remains even if your app is killed off.

Google's Storage Options guide is also definitely worth a look if you haven't had a chance to review it yet.

To save a String you would use:

String str = "abc";
getSharedPreferences("filename", Context.MODE_PRIVATE).edit().putString("String Name", str).commit();

And then to retrieve it:

String str = getSharedPreferences("filename", Context.MODE_PRIVATE).getString("String Name", "default string")