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解决方案：对于onSaveInstanceState中的自定义类保存，您可以将类转换为JSON字符串并使用Gson转换进行恢复，对于单字符串、双精度、Int、Long值保存和恢复，如下所示。以下示例适用于片段和活动：
对于活动：
对于将数据放入saveInstanceState：
override fun onSaveInstanceState(outState: Bundle) {
super.onSaveInstanceState(outState)
//for custom class-----
val gson = Gson()
val json = gson.toJson(your_custom_class)
outState.putString("CUSTOM_CLASS", json)
//for single value------
outState.putString("MyString", stringValue)
outState.putBoolean("MyBoolean", true)
outState.putDouble("myDouble", doubleValue)
outState.putInt("MyInt", intValue)
}
还原数据：
override fun onRestoreInstanceState(savedInstanceState: Bundle) {
super.onRestoreInstanceState(savedInstanceState)
//for custom class restore
val json = savedInstanceState?.getString("CUSTOM_CLASS")
if (!json!!.isEmpty()) {
val gson = Gson()
testBundle = gson.fromJson(json, Session::class.java)
}
//for single value restore
val myBoolean: Boolean = savedInstanceState?.getBoolean("MyBoolean")
val myDouble: Double = savedInstanceState?.getDouble("myDouble")
val myInt: Int = savedInstanceState?.getInt("MyInt")
val myString: String = savedInstanceState?.getString("MyString")
}
您也可以在Activity onCreate上恢复它。
对于碎片：
对于saveInstanceState中的put类：
override fun onSaveInstanceState(outState: Bundle) {
super.onSaveInstanceState(outState)
val gson = Gson()
val json = gson.toJson(customClass)
outState.putString("CUSTOM_CLASS", json)
}
还原数据：
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
//for custom class restore
if (savedInstanceState != null) {
val json = savedInstanceState.getString("CUSTOM_CLASS")
if (!json!!.isEmpty()) {
val gson = Gson()
val customClass: CustomClass = gson.fromJson(json, CustomClass::class.java)
}
}
// for single value restore
val myBoolean: Boolean = savedInstanceState.getBoolean("MyBoolean")
val myDouble: Double = savedInstanceState.getDouble("myDouble")
val myInt: Int = savedInstanceState.getInt("MyInt")
val myString: String = savedInstanceState.getString("MyString")
}
Kotlin解决方案：对于onSaveInstanceState中的自定义类保存，您可以将类转换为JSON字符串并使用Gson转换进行恢复，对于单字符串、双精度、Int、Long值保存和恢复，如下所示。以下示例适用于片段和活动：
对于活动：
对于将数据放入saveInstanceState：
override fun onSaveInstanceState(outState: Bundle) {
super.onSaveInstanceState(outState)
//for custom class-----
val gson = Gson()
val json = gson.toJson(your_custom_class)
outState.putString("CUSTOM_CLASS", json)
//for single value------
outState.putString("MyString", stringValue)
outState.putBoolean("MyBoolean", true)
outState.putDouble("myDouble", doubleValue)
outState.putInt("MyInt", intValue)
}
还原数据：
override fun onRestoreInstanceState(savedInstanceState: Bundle) {
super.onRestoreInstanceState(savedInstanceState)
//for custom class restore
val json = savedInstanceState?.getString("CUSTOM_CLASS")
if (!json!!.isEmpty()) {
val gson = Gson()
testBundle = gson.fromJson(json, Session::class.java)
}
//for single value restore
val myBoolean: Boolean = savedInstanceState?.getBoolean("MyBoolean")
val myDouble: Double = savedInstanceState?.getDouble("myDouble")
val myInt: Int = savedInstanceState?.getInt("MyInt")
val myString: String = savedInstanceState?.getString("MyString")
}
您也可以在Activity onCreate上恢复它。
对于碎片：
对于saveInstanceState中的put类：
override fun onSaveInstanceState(outState: Bundle) {
super.onSaveInstanceState(outState)
val gson = Gson()
val json = gson.toJson(customClass)
outState.putString("CUSTOM_CLASS", json)
}
还原数据：
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
//for custom class restore
if (savedInstanceState != null) {
val json = savedInstanceState.getString("CUSTOM_CLASS")
if (!json!!.isEmpty()) {
val gson = Gson()
val customClass: CustomClass = gson.fromJson(json, CustomClass::class.java)
}
}
// for single value restore
val myBoolean: Boolean = savedInstanceState.getBoolean("MyBoolean")
val myDouble: Double = savedInstanceState.getDouble("myDouble")
val myInt: Int = savedInstanceState.getInt("MyInt")
val myString: String = savedInstanceState.getString("MyString")
}
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
}
