Question

获得活动状态时遇到问题。我有2个活动：MainActivity和Activity2。在MainActivity中，我将editText和button名称设为GO。在Activity2中，我有一个button名称BackMainActivity。我想要的是：我把一个文本，例如：“abc”到EditText然后点击按钮GO。应用程序将导航到Activity2。之后，我点击BackMainActivity按钮，应用程序将导航到MainActivity，EditText中的数据将恢复为“abc”。我已经使用过onSaveInstanceState和onRestoreInstanceState。应用程序在转到Activity2之前运行onSaveInstanceState。但是如果我回到MainActivity，onCreate（），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？非常感谢你！

MainActivity

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();
    }
}

活性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中

<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

做一些像：

1：从onSavedInstanceState中的oncreate()获取数据并将其放入edittext。类似的东西：

 @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Activity2中设置一个FLAG_ACTIVITY_REORDER_TO_FRONT标记，其中包含您的意图。

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

为了更好的主意，请查看此conversation。

Answer 2

在Activity2的onClick功能中，您不必返回上一个MainActivity但是您打开一个新的MainActivity。

通过调用finish（）完成Activity2，然后您的第一个MainActivity将再次出现。它应该使用设备的硬件后退按钮。

Bundle savedInstanceState在onCreate（）上为null，尽管savedInstanceState已经设置了数据

2 个答案: