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。
解决这个问题的简单快捷方法是使用IcePick
首先，在app/build.gradle中设置库
repositories {
maven {url "https://clojars.org/repo/"}
}
dependencies {
compile 'frankiesardo:icepick:3.2.0'
provided 'frankiesardo:icepick-processor:3.2.0'
}
现在，让我们看看下面的示例，如何在“活动”中保存状态
public class ExampleActivity extends Activity {
@State String username; // This will be automatically saved and restored
@Override public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Icepick.restoreInstanceState(this, savedInstanceState);
}
@Override public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
Icepick.saveInstanceState(this, outState);
}
}
它适用于Activities、Fragments或任何需要在Bundle上序列化其状态的对象（例如，迫击炮的ViewPresenter）
Icepick还可以为自定义视图生成实例状态代码：
class CustomView extends View {
@State int selectedPosition; // This will be automatically saved and restored
@Override public Parcelable onSaveInstanceState() {
return Icepick.saveInstanceState(this, super.onSaveInstanceState());
}
@Override public void onRestoreInstanceState(Parcelable state) {
super.onRestoreInstanceState(Icepick.restoreInstanceState(this, state));
}
// You can put the calls to Icepick into a BaseCustomView and inherit from it
// All Views extending this CustomView automatically have state saved/restored
}
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
