它的主要功能有两个：

o 监听来自AppWidgetService的事件。

o 另外一个功能就是创建AppWidgetHostView。

       前面我们说过RemoteViews不是真正的View，只是View的描述，而 AppWidgetHostView才是真正的View。这里先创建AppWidgetHostView，然后通过AppWidgetService查询 appWidgetId对应的RemoteViews，最后把RemoteViews传递给AppWidgetHostView去updateAppWidget。

Host的实现者

<!-- Copyright (C) 2006 The Android Open Source Project

 

Licensed under the Apache License, Version 2.0 (the "License");

you may not use this file except in compliance with the License.

You may obtain a copy of the License at

 

http://www.apache.org/licenses/LICENSE-2.0

 

Unless required by applicable law or agreed to in writing, software

distributed under the License is distributed on an "AS IS" BASIS,

WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

See the License for the specific language governing permissions and

limitations under the License.

-->

 

<appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"

android:minWidth="60dp"

android:minHeight="30dp"

android:updatePeriodMillis="86400000"

android:initialLayout="@layout/appwidget_provider"

android:configure="com.example.android.apis.appwidget.ExampleAppWidgetConfigure"

>

</appwidget-provider>

 

    如果你需要一个带有Button的App Widget，点击Button去启动一个Activity，下面就是AppWidgetProvider的实现方法：

public class ExampleAppWidgetProvider extends AppWidgetProvider { 

public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) { 

final int N = appWidgetIds.length; 

// Perform this loop procedure for each App Widget that belongs to this provider 

for (int i=0; i<N; i++) { 

int appWidgetId = appWidgetIds[i]; 

// Create an Intent to launch ExampleActivity 

Intent intent = new Intent(context, ExampleActivity.class); 

PendingIntent pendingIntent = PendingIntent.getActivity(context, 0, intent, 0); 

// Get the layout for the App Widget and attach an on-click listener to the button 

RemoteViews views = new RemoteViews(context.getPackageName(), R.layout.appwidget_provider_layout); 

views.setOnClickPendingIntent(R.id.button, pendingIntent); 

// Tell the AppWidgetManager to perform an update on the current App Widget 

appWidgetManager.updateAppWidget(appWidgetId, views); 

    } 

  } 

}

<?xml version="1.0" encoding="utf-8"?>

<!-- Copyright (C) 2006 The Android Open Source Project

 

Licensed under the Apache License, Version 2.0 (the "License");

you may not use this file except in compliance with the License.

You may obtain a copy of the License at

 

http://www.apache.org/licenses/LICENSE-2.0

 

Unless required by applicable law or agreed to in writing, software

distributed under the License is distributed on an "AS IS" BASIS,

WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

See the License for the specific language governing permissions and

limitations under the License.

-->

 

<TextView xmlns:android="http://schemas.android.com/apk/res/android"

android:id="@+id/appwidget_text"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:textColor="#ff000000"

/>

<activity android:name=".ExampleAppWidgetConfigure"> 

 <intent-filter> 

 <action android:name="android.appwidget.action.APPWIDGET_CONFIGURE"    /> 

</intent-filter> 

</activity>

/*
 * Copyright (C) 2008 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.apis.appwidget;

import android.app.Activity;
import android.appwidget.AppWidgetManager;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;

import java.util.ArrayList;

// Need the following import to get access to the app resources, since this
// class is in a sub-package.
import com.example.android.apis.R;

/**
 * The configuration screen for the ExampleAppWidgetProvider widget sample.
 */
public class ExampleAppWidgetConfigure extends Activity {
    static final String TAG = "ExampleAppWidgetConfigure";

    private static final String PREFS_NAME
            = "com.example.android.apis.appwidget.ExampleAppWidgetProvider";
    private static final String PREF_PREFIX_KEY = "prefix_";

    int mAppWidgetId = AppWidgetManager.INVALID_APPWIDGET_ID;
    EditText mAppWidgetPrefix;

    public ExampleAppWidgetConfigure() {
        super();
    }

    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);

        // Set the result to CANCELED. This will cause the widget host to cancel
        // out of the widget placement if they press the back button.
        setResult(RESULT_CANCELED);

        // Set the view layout resource to use.
        setContentView(R.layout.appwidget_configure);

        // Find the EditText
        mAppWidgetPrefix = (EditText)findViewById(R.id.appwidget_prefix);

        // Bind the action for the save button.
        findViewById(R.id.save_button).setOnClickListener(mOnClickListener);

        // Find the widget id from the intent. 
        Intent intent = getIntent();
        Bundle extras = intent.getExtras();
        if (extras != null) {
            mAppWidgetId = extras.getInt(
                    AppWidgetManager.EXTRA_APPWIDGET_ID, AppWidgetManager.INVALID_APPWIDGET_ID);
        }

        // If they gave us an intent without the widget id, just bail.
        if (mAppWidgetId == AppWidgetManager.INVALID_APPWIDGET_ID) {
            finish();
        }

        mAppWidgetPrefix.setText(loadTitlePref(ExampleAppWidgetConfigure.this, mAppWidgetId));
    }

    View.OnClickListener mOnClickListener = new View.OnClickListener() {
        public void onClick(View v) {
            final Context context = ExampleAppWidgetConfigure.this;

            // When the button is clicked, save the string in our prefs and return that they
            // clicked OK.
            String titlePrefix = mAppWidgetPrefix.getText().toString();
            saveTitlePref(context, mAppWidgetId, titlePrefix);

            // Push widget update to surface with newly set prefix
            AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(context);
            ExampleAppWidgetProvider.updateAppWidget(context, appWidgetManager,
                    mAppWidgetId, titlePrefix);

            // Make sure we pass back the original appWidgetId
            Intent resultValue = new Intent();
            resultValue.putExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, mAppWidgetId);
            setResult(RESULT_OK, resultValue);
            finish();
        }
    };

    // Write the prefix to the SharedPreferences object for this widget
    static void saveTitlePref(Context context, int appWidgetId, String text) {
        SharedPreferences.Editor prefs = context.getSharedPreferences(PREFS_NAME, 0).edit();
        prefs.putString(PREF_PREFIX_KEY + appWidgetId, text);
        prefs.commit();
    }

    // Read the prefix from the SharedPreferences object for this widget.
    // If there is no preference saved, get the default from a resource
    static String loadTitlePref(Context context, int appWidgetId) {
        SharedPreferences prefs = context.getSharedPreferences(PREFS_NAME, 0);
        String prefix = prefs.getString(PREF_PREFIX_KEY + appWidgetId, null);
        if (prefix != null) {
            return prefix;
        } else {
            return context.getString(R.string.appwidget_prefix_default);
        }
    }

    static void deleteTitlePref(Context context, int appWidgetId) {
    }

    static void loadAllTitlePrefs(Context context, ArrayList<Integer> appWidgetIds,
            ArrayList<String> texts) {
    }
}