我一直在做Android SDK平台,对如何保存应用程序的状态有点不清楚。因此,考虑到“Hello, Android”示例的这个小的重新工具:
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就足够了,但无论我如何离开应用程序,它总是以第一条消息响应。
我确信解决方案就像覆盖 onPause
或类似的东西一样简单,但我已经在文档中查找了 30 分钟左右,但没有发现任何明显的东西。
最佳答案
您需要覆盖 onSaveInstanceState(Bundle savedInstanceState)
并将要更改的应用程序状态值写入 Bundle
参数,如下所示:
@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
super.onSaveInstanceState(savedInstanceState);
// Save UI state changes to the savedInstanceState.
// This bundle will be passed to onCreate if the process is
// killed and restarted.
savedInstanceState.putBoolean("MyBoolean", true);
savedInstanceState.putDouble("myDouble", 1.9);
savedInstanceState.putInt("MyInt", 1);
savedInstanceState.putString("MyString", "Welcome back to Android");
// etc.
}
Bundle 本质上是一种存储 NVP(“名称-值对”)映射的方法,它将被传递到 onCreate()
和 onRestoreInstanceState()
然后你可以从这样的 Activity 中提取值:
@Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
// Restore UI state from the savedInstanceState.
// This bundle has also been passed to onCreate.
boolean myBoolean = savedInstanceState.getBoolean("MyBoolean");
double myDouble = savedInstanceState.getDouble("myDouble");
int myInt = savedInstanceState.getInt("MyInt");
String myString = savedInstanceState.getString("MyString");
}
或者来自 fragment 。
@Override
public void onViewStateRestored(@Nullable Bundle savedInstanceState) {
super.onViewStateRestored(savedInstanceState);
// Restore UI state from the savedInstanceState.
// This bundle has also been passed to onCreate.
boolean myBoolean = savedInstanceState.getBoolean("MyBoolean");
double myDouble = savedInstanceState.getDouble("myDouble");
int myInt = savedInstanceState.getInt("MyInt");
String myString = savedInstanceState.getString("MyString");
}
您通常会使用这种技术来存储应用程序的实例值(选择、未保存的文本等)。
关于android - 如何使用保存实例状态保存 Activity 状态?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/9805175/