Android：切换纵向和横向时保存和恢复活动数据

Question

我尝试将我的卷号和名称保存在主要活动中，但是当我的屏幕旋转时，活动数据已丢失，

我终于修好了，下面我添加源代码

Answer 1

考虑任何布局，这里我使用这种布局结构

在activity_xml中：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="20dp"
    tools:context=".MainActivity">
    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">
        <TextView
            android:id="@+id/rollnoID"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="15dp"
            android:layout_marginTop="10dp"
            android:text="Rollno : "
            android:textSize="25dp" />

        <EditText
            android:hint="Roll Number"
            android:id="@+id/rollnoID_edit"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="15dp"
            android:layout_marginTop="10dp"
            android:ems="8"
            android:inputType="number"
            android:text=""
            android:textSize="25dp" />
    </LinearLayout>
    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">
        <TextView
            android:id="@+id/nameID"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="15dp"
            android:layout_marginTop="10dp"
            android:text="Name : "
            android:textSize="25dp" />
        <EditText
            android:hint="Student Name"
            android:id="@+id/nameID_edit"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="15dp"
            android:layout_marginTop="10dp"
            android:ems="8"
            android:inputType="textCapWords"
            android:text=""
            android:textSize="25dp" />
    </LinearLayout>
    <Button
        android:onClick="saveData"
        android:id="@+id/saveButton"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="save this Data"
        android:textSize="20sp" />
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginTop="20dp"
        android:padding="20dp"
        android:orientation="vertical">
        <TextView
            android:gravity="center"
            android:hint="~RollNo~"
            android:textColor="@color/colorPrimary"
            android:id="@+id/display_rollno"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:textSize="30sp" />
        <TextView
            android:layout_marginTop="20dp"
            android:id="@+id/display_name"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:hint="~Name~"
            android:textColor="@color/colorPrimary"
            android:textSize="30sp" />
    </LinearLayout>
</LinearLayout>

在 MainActivity 中：

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    private static final String KEY_ROLL = "rollno_key";
    private static final String KEY_NAME = "name_key";

    int rollno;
    String name;

    EditText roll_et , name_et;
    TextView roll_tv , name_tv;
    Button saveButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        roll_et = (EditText) findViewById(R.id.rollnoID_edit);
        name_et = (EditText) findViewById(R.id.nameID_edit);

        roll_tv = (TextView) findViewById(R.id.display_rollno);
        name_tv = (TextView) findViewById(R.id.display_name);

        if (savedInstanceState != null){
            String save_RollNO = savedInstanceState.getString(KEY_ROLL);
            roll_tv.setText(save_RollNO);

            String save_Name = savedInstanceState.getString(KEY_NAME);
            name_tv.setText(save_Name);
        } else {
            Toast.makeText(getApplicationContext(),"Entry your data",Toast.LENGTH_SHORT).show();
        }

    }

    @Override
    public void onSaveInstanceState(Bundle saveData) {
        saveData.putString(KEY_ROLL , roll_et.getText().toString());
        saveData.putString(KEY_NAME , name_et.getText().toString());
        super.onSaveInstanceState(saveData);
    }

    public void saveData(View v){
        roll_tv.setText(roll_et.getText().toString().trim());
        name_tv.setText(name_et.getText().toString().trim());
    }
}