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Android Studio屏幕方向以及UI界面状态的保存代码详解
来源:jb51  时间:2019/11/1 8:32:53  对本文有异议

项目: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 {
/*
  = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
  本实例主要学习,屏幕翻转时,界面如何自适应,创建横屏布局
  1.禁止切换横屏:在 AndroidManifest.xml-->application->activity->中设置如下代码(android:screenOrientation="portrait")
   <activity android:name=".MainActivity" android:screenOrientation="portrait" >
  2. 创建 Landscape 布局,横屏时,会自动加载 Landscape 的布局界面(清单文件中,注意去掉 android:screenOrientation="portrait" )
  3. 翻转屏幕时,保存窗口控件的状态值;
 
  = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
 */
  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);
 
    //如果State中的值不为空,如果有相应的这个组件的值,则读取出来赋值上去
    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
  //将 textView 中的值,先保存到 outState 中(键值对)
  public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putString("key",textView.getText().toString());
  }
}

扩展学习:

UI界面设计

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" />

要想使得文字居中,需要添加属性android:gravity="center",可选择的选项还有top、bottom、left、right、center等,center相当于center_vertical|center_horizontal。
使用android:textSize="24sp"指定文字大小,android:textColor="#00ff00"指定文字颜色。

Button

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

在Android中,Button上面的文字默认英文全部大写,可以通过设置android:textAllCaps="false"改变

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" />

通过设置hint属性可以得到提示文字,设置maxLines使得输入框中最大输入行数。

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