Detailed explanation of saving code of Android Studio screen direction and UI interface state

Project: Orientation

package com.example.orientation;
 
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
 
import androidx.appcompat.app.AppCompatActivity;
 
public class MainActivity extends AppCompatActivity {
/*
  = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
   This example mainly learns how to adapt the interface and create a horizontal screen layout when the screen is flipped 
  1. Prohibit switching horizontal screen: in  AndroidManifest.xml-->application->activity-> Set the following code in ( android:screenOrientation="portrait" ) 
   <activity android:name=".MainActivity" android:screenOrientation="portrait" >
  2.  Create  Landscape  Layout, horizontal screen, will automatically load  Landscape  The layout interface of (in the manifest file, pay attention to remove it  android:screenOrientation="portrait"  ) 
  3.  Save the state value of the window control when flipping the screen ;
 
  = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
 */
  Button button;
  TextView textView;
 
  String TAG = "myTag";
 
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
 
    button = findViewById(R.id.button );
    textView = findViewById(R.id.textView);
 
    // If State The value in is not empty. If there is a corresponding value of this component, read it out and assign it 
    if(savedInstanceState !=null)
    {
      String s = savedInstanceState.getString("key");
      textView.setText(s);
    }
 
    button.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View view) {
        textView.setText(button.getText());
      }
    });
  }
 
  @Override
  protected void onDestroy() {
    super.onDestroy();
    Log.d(TAG,"onDestroy:");
  }
 
  @Override
  // Will  textView  The value in, first save to the value in  outState  Medium (key-value pair) 
  public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putString("key",textView.getText().toString());
  }
}

Extended learning:

UI Interface Design

TextView

<TextView
    android:id="@+id/textview"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:gravity="center"
    android:text="This is a TextView"
    android:textColor="#00ff00"
    android:textSize="24sp" />

To center the text, you need to add the attribute android: gravity= "center", and the options you can choose are top, bottom, left, right, center, etc. center is equivalent to center_verticalcenter_horizontal.
Use android: textSize= "24sp" to specify the text size and android: textColor= "# 00ff00" to specify the text color.

Button

<Button
    android:id="@+id/button"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Button"
    android:textAllCaps="false"/>

In Android, the text above Button is all capitalized by default, which can be changed by setting android: textAllCaps = "false"

EditText

<EditText
    android:id="@+id/edittext"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="HelloWorld"
    android:maxLength="20"
    android:maxLines="1" />

Prompt text can be obtained by setting hint property, and setting maxLines makes the maximum number of input lines in the input box.

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