onCreate（）上的Bundle savedInstanceState为null，尽管savedInstanceState已设置为数据

Question

我在获取活动状态时遇到问题。我有两个活动：主要活动和活动2。在MainActivity中，我放置了一个editText和一个按钮name GO。在Activity2中，我有一个按钮namebackmain活动。我想要的是：我把一个文本，例如：“abc”放入EditText，然后单击GO按钮。应用程序将导航到Activity2。之后，我点击按钮BackMainActivity，应用程序将导航到MainActivity，EditText中的数据恢复为“abc”。我已经使用了onSaveInstanceState和onRestoreInstanceState。在转到Activity2之前，应用程序运行onSaveInstanceState。但如果我返回MainActivity，onCreate（），则savedInstanceState为null。你能告诉我原因吗？我想在bundle中存储mainActivity的数据。那我该怎么办呢？非常感谢你！

主要活动

package com.example.demosavedataactivity;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends Activity {

    EditText t;
    Button b;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        t = (EditText) findViewById(R.id.editText1);
        b = (Button) findViewById(R.id.button1);
        b.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                Intent intent = new Intent(MainActivity.this, Activity2.class);
                startActivity(intent);
            }
        });

    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        // TODO Auto-generated method stub
        String a =  t.getText().toString();
        outState.putString("text",a);

        super.onSaveInstanceState(outState);
    }

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        // TODO Auto-generated method stub

        t.setText(savedInstanceState.getString("text"));
        super.onRestoreInstanceState(savedInstanceState);
    }

    @Override
    protected void onDestroy() {
        // TODO Auto-generated method stub
        Log.w("<<<<<<<<<<<<<<<<<<<", "onDestroy");
        super.onDestroy();
    }

    @Override
    protected void onPause() {
        // TODO Auto-generated method stub
        Log.w("<<<<<<<<<<<<<<<<<<<", "onPause");
        super.onPause();
    }

    @Override
    protected void onRestart() {
        // TODO Auto-generated method stub
        Log.w("<<<<<<<<<<<<<<<<<<<", "onRestart");
        super.onRestart();
    }

    @Override
    protected void onResume() {
        // TODO Auto-generated method stub
        Log.w("<<<<<<<<<<<<<<<<<<<", "onResume");
        super.onResume();
    }

    @Override
    protected void onStart() {
        // TODO Auto-generated method stub
        Log.w("<<<<<<<<<<<<<<<<<<<", "onStart");
        super.onStart();
    }

    @Override
    protected void onStop() {
        // TODO Auto-generated method stub
        Log.w("<<<<<<<<<<<<<<<<<<<", "onStop");
        super.onStop();
    }
}

活动2

package com.example.demosavedataactivity;    
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.Button;

public class Activity2 extends Activity {

    Button back;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity2);
        back = (Button) findViewById(R.id.button1);
        back.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                Intent intent = new Intent(Activity2.this, MainActivity.class);
                startActivity(intent);
            }
        });
    }

}

activity2.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="CombackA1" />

</LinearLayout>

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <EditText
        android:id="@+id/editText1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="14dp"
        android:layout_marginTop="18dp"
        android:ems="10" />

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/editText1"
        android:layout_below="@+id/editText1"
        android:layout_marginLeft="50dp"
        android:layout_marginTop="63dp"
        android:text="Button" />

</RelativeLayout>

Answer 1

只需做如下操作：

1：从您的oncreate（）中的onSavedInstanceState获取数据，并将其放入您的edittext。比如：

 @Override
 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    t = (EditText) findViewById(R.id.editText1);
    b = (Button) findViewById(R.id.button1);

    /*Just fetch data from savedInstanceState */
    if(savedInstanceState != null){
         t.setText(savedInstanceState.getString("text"));
    }
    b.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            Intent intent = new Intent(MainActivity.this, Activity2.class);              
            startActivity(intent);
        }
    });
  }

在你的Activity2中，根据你的意图设置一个FLAG\u ACTIVITY\u REORDER\u TO\u FRONT标志。例如：

 Intent intent = new Intent(Activity2.this, MainActivity.class);
 intent.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
 startActivity(intent);

想知道更好的主意，请查看此对话。