android 全局变量Application类使用

新建一个项目

一 新建一个class 继承Application类

package com.application.kzp.example.applicationclasstest;import android.app.Application;public class MyApplication extends Application {    private String value;    @Override    public void onCreate() {        super.onCreate();        value="";    }    public void setValue(String value) {        this.value = value;    }    public String getValue() {        return value;    }}

二 MainActivity.java

package com.application.kzp.example.applicationclasstest;import android.content.Intent;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;public class MainActivity extends AppCompatActivity {    MyApplication app;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        app= (MyApplication) getApplication();        app.setValue("改变了");        Intent intent=new Intent(MainActivity.this,Main2Activity.class);        startActivity(intent);        finish();    }}
三 Main2Activity.java
新建一个activity
package com.application.kzp.example.applicationclasstest;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.widget.TextView;public class Main2Activity extends AppCompatActivity {    MyApplication app;    TextView textView;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main2);        app= (MyApplication) getApplication();        textView= (TextView) findViewById(R.id.text);        String value=app.getValue();        textView.setText(value);    }}

main2_activity.xml
<?xml version="1.0" encoding="utf-8"?><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:paddingLeft="@dimen/activity_horizontal_margin"    android:paddingRight="@dimen/activity_horizontal_margin"    android:paddingTop="@dimen/activity_vertical_margin"    android:paddingBottom="@dimen/activity_vertical_margin"    tools:context="com.application.kzp.example.applicationclasstest.Main2Activity">    <TextView        android:id="@+id/text"        android:layout_width="wrap_content"        android:layout_height="wrap_content" /></RelativeLayout>

这样我们就设置了一个全局变量value

运行就可以看到效果，也可以自己添加一个按钮再跳转页面那样效果更明显