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")

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

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

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

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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