我一直在安卓SDK平台上工作，现在还不清楚如何保存应用程序的状态。因此，考虑到“你好，Android”示例的这个小的重新设计：
package com.android.hello;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
public class HelloAndroid extends Activity {
private TextView mTextView = null;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mTextView = new TextView(this);
if (savedInstanceState == null) {
mTextView.setText("Welcome to HelloAndroid!");
} else {
mTextView.setText("Welcome back.");
}
setContentView(mTextView);
}
}
我认为这对于最简单的情况来说已经足够了，但无论我如何离开应用程序，它总是以第一条消息来响应。
我确信解决方案就像重写onPause之类的东西一样简单，但我已经在文档中翻了大约30分钟，没有发现任何明显的东西。
Kotlin代码：
保存：
override fun onSaveInstanceState(outState: Bundle) {
super.onSaveInstanceState(outState.apply {
putInt("intKey", 1)
putString("stringKey", "String Value")
putParcelable("parcelableKey", parcelableObject)
})
}
然后在onCreate（）或onRestoreInstanceState（）中
val restoredInt = savedInstanceState?.getInt("intKey") ?: 1 //default int
val restoredString = savedInstanceState?.getString("stringKey") ?: "default string"
val restoredParcelable = savedInstanceState?.getParcelable<ParcelableClass>("parcelableKey") ?: ParcelableClass() //default parcelable
如果不想有Optionals，请添加默认值
我的问题是，我只在应用程序生命周期内需要持久性（即一次执行，包括在同一应用程序内启动其他子活动和旋转设备等）。我尝试了以上答案的各种组合，但在所有情况下都没有得到我想要的答案。最后，对我有用的是在onCreate期间获取savedInstanceState的引用：
mySavedInstanceState=savedInstanceState;
并在需要时使用它来获取变量的内容，如下所示：
if (mySavedInstanceState !=null) {
boolean myVariable = mySavedInstanceState.getBoolean("MyVariable");
}
如上所述，我使用了onSaveInstanceState和onRestoreInstanceState，但我想我也可以或替代地使用我的方法在变量更改时保存变量（例如，使用putBoolean）
使用Android ViewModel和SavedStateHandle持久化可序列化数据
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ActivityMainBinding binding = ActivityMainBinding.inflate(getLayoutInflater());
binding.setViewModel(new ViewModelProvider(this).get(ViewModel.class));
binding.setLifecycleOwner(this);
setContentView(binding.getRoot());
}
public static class ViewModel extends AndroidViewModel {
//This field SURVIVE the background process reclaim/killing & the configuration change
public final SavedStateHandle savedStateHandle;
//This field NOT SURVIVE the background process reclaim/killing but SURVIVE the configuration change
public final MutableLiveData<String> inputText2 = new MutableLiveData<>();
public ViewModel(@NonNull Application application, SavedStateHandle savedStateHandle) {
super(application);
this.savedStateHandle = savedStateHandle;
}
}
}
在布局文件中
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">
<data>
<variable
name="viewModel"
type="com.xxx.viewmodelsavedstatetest.MainActivity.ViewModel" />
</data>
<LinearLayout xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".MainActivity">
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:autofillHints=""
android:hint="This field SURVIVE the background process reclaim/killing & the configuration change"
android:text='@={(String)viewModel.savedStateHandle.getLiveData("activity_main/inputText", "")}' />
<SeekBar
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:max="100"
android:progress='@={(Integer)viewModel.savedStateHandle.getLiveData("activity_main/progress", 50)}' />
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="This field SURVIVE the background process reclaim/killing & the configuration change"
android:text='@={(String)viewModel.savedStateHandle.getLiveData("activity_main/inputText", "")}' />
<SeekBar
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:max="100"
android:progress='@={(Integer)viewModel.savedStateHandle.getLiveData("activity_main/progress", 50)}' />
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="This field NOT SURVIVE the background process reclaim/killing but SURVIVE the configuration change"
android:text='@={viewModel.inputText2}' />
</LinearLayout>
</layout>
测试：
1. start the test activity
2. press home key to go home
3. adb shell kill <the test activity process>
4. open recent app list and restart the test activity
