完全理解Android中的RemoteViews

一、什麼是RemoteViews

RemoteViews翻譯過來就是遠程視圖.顧名思義,RemoteViews不是當前進程的View,是屬於SystemServer進程.應用程序與RemoteViews之間依賴Binder實現了進程間通信.

二、RemoteViews的用法

RemoteViews使用最多的場合是通知欄和桌面小插件. 以通知欄爲例,講解下它的用法.

1、新建一個Notification

這裏要注意是在android3.0之前都是使用如下的形式構建一個Notification

        // 1.新建一個Notification對象
        Notification mNotification = new Notification();
        // 2.添加屬性,比如標題、內容、優先級、圖片等
        mNotification.tickerText = "這是通知欄的標題";
        mNotification.icon = R.drawable.ic_launcher;
        mNotification.flags=Notification.FLAG_NO_CLEAR;
        mNotification.setLatestEventInfo(this, "這是內容", "這是標題", null);

在3.0之後官方推薦使用建造者模式創建Notification.

Notification mNotification = new Notification.Builder(this)
        .setContentTitle("這是標題 ")    
        .setContentText("這是內容")        
        .setSmallIcon(R.drawable.ic_launcher)                
        .build();

Notification有很多屬性,這裏列舉一些

 - setContentTitle       設置標題
 - setContentText        設置內容
 - setLargeIcon          設置通知欄大圖標
 - setSmallIcon          設置通知欄小圖標
 - setContent            設置RemoteViews
 - setContentIntent      當通知條目被點擊，就執行這個被設置的Intent.
 - setDeleteIntent       當用戶點擊"Clear All Notifications"按鈕區刪除所有的通知的時候，這個被設置的Intent被執行
 - setLights             設置閃光燈
 - setSound              設置聲音
 - setPriority           設置優先級

2、設置Notification的RemoteViews

如果要給通知欄使用自定義佈局就要使用RemoteViews了,傳入包名和相應的佈局.

RemoteViews mRemoteViews=new RemoteViews("com.example.remoteviewdemo", R.layout.remoteview_layout);

然後通過setContent()傳入RemoteViews 對象即可.

這裏順便講一下PendingIntent,PendingIntent是”延遲意圖”的意思,就是當滿足某一條件時出觸發這個Intent.通過PendingIntent的getActivity、getBroadcast、getService等分別構建一個打開對應組件的延遲Intent.
傳入四個參數，context、intent、requestCode(自定義)、flag.

Intent intent=new Intent(MainActivity.this,MainActivity.class);
PendingIntent mPendingIntent=PendingIntent.getActivity(MainActivity.this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);

PendingIntent有4種flag.

 - FLAG_ONE_SHOT                只執行一次
 - FLAG_NO_CREATE               若描述的Intent不存在則返回NULL值
 - FLAG_CANCEL_CURRENT          如果描述的PendingIntent已經存在，則在產生新的Intent之前會先取消掉當前的
 - FLAG_UPDATE_CURRENT          總是執行,這個flag用的最多

3、獲取通知管理者

NotificationManager manager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

4、彈出通知

調用notify方法,傳入一個id(自定義)和通知實例即可.

manager.notify(1, mNotification);

5、例子

我用一個按鈕彈出通知,點擊這個通知時進入到該Activity

public class MainActivity extends Activity {

    private NotificationManager manager;
    private Notification mNotification;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //1.創建RemoteViews實例
        RemoteViews mRemoteViews=new RemoteViews("com.example.remoteviewdemo", R.layout.remoteview_layout);

        //2.構建一個打開Activity的PendingIntent
        Intent intent=new Intent(MainActivity.this,MainActivity.class);
        PendingIntent mPendingIntent=PendingIntent.getActivity(MainActivity.this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);

        //3.創建一個Notification
        mNotification = new Notification.Builder(this)
        .setSmallIcon(R.drawable.ic_launcher)
        .setContentIntent(mPendingIntent)
        .setContent(mRemoteViews)
        .build();

        //4.獲取NotificationManager
        manager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

        Button button1 = (Button) findViewById(R.id.button1);
        button1.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                //彈出通知
                manager.notify(1, mNotification);
            }
        });

    }
}

如下圖

6、改變RemoteViews的佈局

RemoteViews並不能直接獲得控件實例,然後對控件進行操作.它提供了
setTextViewText(viewId, text)、setImageViewResource(viewId, srcId)等方法進行操作,傳入控件id和相應的修改內容.
列舉一下常用的屬性

 - setTextViewText(viewId, text)                     設置文本
 - setTextColor(viewId, color)                       設置文本顏色
 - setTextViewTextSize(viewId, units, size)          設置文本大小 
 - setImageViewBitmap(viewId, bitmap)                設置圖片
 - setImageViewResource(viewId, srcId)               根據圖片資源設置圖片
 - setViewPadding(viewId, left, top, right, bottom)  設置Padding間距
 - setOnClickPendingIntent(viewId, pendingIntent)    設置點擊事件 

我這裏就以setTextViewText改變文本的屬性來講解改變RemoteViews的原理.
我在原來的代碼上加上一個按鈕點擊改變內容

Button button2 = (Button) findViewById(R.id.button2);
button2.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                mRemoteViews.setTextViewText(R.id.remote_content, "改變了內容");
                manager.notify(1, mNotification);
            }
        });

看下效果

三、RemoteViews的改變原理

1.setTextViewText方法代碼如下

public class RemoteViews implements Parcelable, Filter {
    ......
public void setTextViewText(int viewId, CharSequence text) {
        setCharSequence(viewId, "setText", text);
    }
    ......
    }

2.調用了setCharSequence方法

public class RemoteViews implements Parcelable, Filter {
    ......
public void setCharSequence(int viewId, String methodName, CharSequence value) {
        addAction(new ReflectionAction(viewId, methodName, ReflectionAction.CHAR_SEQUENCE, value));
    }
     ......
    }

3.在setCharSequence方法裏調用了addAction方法,傳入一個ReflectionAction實例，ReflectionAction繼承自Action,它是用反射調用的

private final class ReflectionAction extends Action {
    ......
    ReflectionAction(int viewId, String methodName, int type, Object value) {
            this.viewId = viewId;
            this.methodName = methodName;
            this.type = type;
            this.value = value;
        }
   ......
   }     

4.看下addAction方法，用了一個集合來保存Action實例,然後更新已使用內存的統計情況

public class RemoteViews implements Parcelable, Filter {
    ......
private void addAction(Action a) {

        if (mActions == null) {
            mActions = new ArrayList<Action>();
        }
        //添加Action
        mActions.add(a);

        // 更新已使用內存的統計情況
        a.updateMemoryUsageEstimate(mMemoryUsageCounter);
    }
    ......
   }   

這一步之後,會調用

manager.notify(1, mNotification);

來更新,追蹤這個notify方法.

public class NotificationManager
{
    ......
public void notify(String tag, int id, Notification notification)
    {
         ......
         INotificationManager service = getService();
         try {
            service.enqueueNotificationWithTag(pkg, mContext.getOpPackageName(), tag, id,
                    stripped, idOut, UserHandle.myUserId());
         ......           
     }
    ......
    }

5.上面會調用getService方法返回INotificationManager這個系統服務,它是在SystemServer進程添加的.然後該服務調用 enqueueNotificationWithTag方法最後層層調用到

public class NotificationManagerService extends INotificationManager.Stub
{
    ......
StatusBarNotification n = new StatusBarNotification(pkg, id, tag, r.uid, r.initialPid, notification);
try {                      mStatusBar.updateNotification(r.statusBarKey, n) 
    }
    ......
    }

新建了StatusBarNotification實例,然後調用updateNotification方法.
這個方法會進入到

public class PhoneStatusBar extends StatusBar {
    ......
public void updateNotification(IBinder key, StatusBarNotification notification) {
    ......
     final RemoteViews contentView = notification.notification.contentView;
    ......
    contentView.reapply(mContext, oldEntry.content);
    ......
    }

會調用StatusBarNotification 的notification.contentView返回RemoteViews 對象,然後調用reapply方法.

6.回到RemoteViews 的reapply方法

public class RemoteViews implements Parcelable, Filter {
    ......
public void reapply(Context context, View v, OnClickHandler handler) {

 RemoteViews rvToApply = getRemoteViewsToApply(context);
 ......
 rvToApply.performApply(v, (ViewGroup) v.getParent(), handler);

    }

private void performApply(View v, ViewGroup parent, OnClickHandler handler) {
        if (mActions != null) {
            handler = handler == null ? DEFAULT_ON_CLICK_HANDLER : handler;
            final int count = mActions.size();
            for (int i = 0; i < count; i++) {
                Action a = mActions.get(i);
                //調用apply方法
                a.apply(v, parent, handler);
            }
        }
    }

     ......
    }

最終調用apply方法,在這裏加載新的佈局,RemoteViews就是這麼完成的.

public class RemoteViews implements Parcelable, Filter {
    ......
public View apply(Context context, ViewGroup parent, OnClickHandler handler) {
RemoteViews rvToApply = getRemoteViewsToApply(context);
        View result;
LayoutInflater inflater =(LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        ......
        //加載佈局
        result = inflater.inflate(rvToApply.getLayoutId(), parent, false);

        rvToApply.performApply(result, parent, handler);

        return result;
    }
     ......
    }

總結

RemoteViews運行在SystemServer進程,更新RemoteViews要通過Binder獲取到對應的服務然後調用RemoteViews內部的apply方法加載更新佈局.