一、简介

桌面小部件，是android提供支持的一种特殊广播，允许在桌面以插件的形式展示内容。

二、示例

1、创建布局文件：此处的布局只使用一个简单的TextView

/layout/layout_widget.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:gravity="center"
    android:orientation="vertical" >
    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="0000-00-00 00:00:00"
        android:textColor="@android:color/background_dark" >
    </TextView>
</LinearLayout>

import java.text.SimpleDateFormat;
import java.util.Date;
import android.app.AlarmManager;
import android.app.PendingIntent;
import android.appwidget.AppWidgetManager;
import android.appwidget.AppWidgetProvider;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.widget.RemoteViews;
import com.am.appwidget.R;
public class TimeWidgetProvider extends AppWidgetProvider {
	private final String UPDATE_ACTION = "TimeWidgetProvider.update.date";

	// 收到请求时执行
	@Override
	public void onReceive(Context context, Intent intent) {
		System.out.println("===onReceive");
		if (intent != null && UPDATE_ACTION.equals(intent.getAction())) {
			updateViews(context);
		}
		super.onReceive(context, intent);
	}

	@Override
	public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
		System.out.println("===onUpdate");
		// 设置定时任务，定时刷新widget
		StartAlarm(context);
	}

	// 删除时调用
	@Override
	public void onDeleted(Context context, int[] appWidgetIds) {
		System.out.println("===onDeleted");
		stopAlarm(context);
	}

	private void StartAlarm(Context context) {
		Intent intent = new Intent(context, TimeWidgetProvider.class);
		intent.setAction(UPDATE_ACTION);
		// AppWidgetProvider 是 BroadcastReceiver 的子类
		PendingIntent refreshIntent = PendingIntent.getBroadcast(context, 0, intent, 0);
		AlarmManager alarm = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
		alarm.setRepeating(AlarmManager.RTC, 0, 1000, refreshIntent);
	}

	private void stopAlarm(Context context) {
		Intent intent = new Intent(context, TimeWidgetProvider.class);
		intent.setAction(UPDATE_ACTION);
		PendingIntent refreshIntent = PendingIntent.getBroadcast(context, 0, intent, 0);
		AlarmManager alarm = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
		alarm.cancel(refreshIntent);
	}

	private void updateViews(Context context) {
		// 只能通过远程对象来设置appwidget中的控件状态
		SimpleDateFormat sf = new SimpleDateFormat("yyy-MM-dd HH:mm:ss");
		String date = sf.format(new Date());
		RemoteViews remoteViews = new RemoteViews(context.getPackageName(), R.layout.layout_widget);
		remoteViews.setTextViewText(R.id.textView1, date);
		// 获得appwidget管理实例，用于管理appwidget以便进行更新操作
		AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(context);
		// 相当于获得所有本程序创建的appwidget
		ComponentName componentName = new ComponentName(context, TimeWidgetProvider.class);
		// 更新appwidget
		appWidgetManager.updateAppWidget(componentName, remoteViews);
	}
}

<?xml version="1.0" encoding="utf-8"?>
<appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
    android:initialLayout="@layout/layout_widget"
    android:minHeight="40dp"
    android:minWidth="80dp"
    android:updatePeriodMillis="0" >
    <!-- updatePeriodMillis:官网的意思如果更新频率大于一次/小时会造成电池寿命问题，设置小了也不起作用，所以在此使用0也就是不更新，后台使用定时任务刷新 -->
</appwidget-provider>

 <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
    	 ... ...
        <!-- 配置AppWidgetProvider -->
        <receiver
            android:name="com.am.appwidget.widget.TimeWidgetProvider"
            android:label="Time App Widget" >
            <!-- 必须显示声明以下action -->
            <intent-filter>
                <action android:name="android.appwidget.action.APPWIDGET_UPDATE" >
                </action>
            </intent-filter>
            <!-- 指定widget的配置文件路径 -->
            <meta-data
                android:name="android.appwidget.provider"
                android:resource="@xml/provider_config" />
        </receiver>
    </application>

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