RemoteViews分析

远程视图，通过该类可实现跨进程更新视图

RemoteViews(String packageName, int layoutId)

packageName

当前进程包名，用于生成ApplicationInfo实例对象

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public RemoteViews(String packageName, int layoutId) {
    this(getApplicationInfo(packageName, UserHandle.myUserId()), layoutId);
}

在该构造方法中调用以下构造方法：

protected RemoteViews(ApplicationInfo application, int layoutId) {
    mApplication = application;
    mLayoutId = layoutId;
    mBitmapCache = new BitmapCache();
    mClassCookies = null;
}

layoutId

通过该id让其它进程获取该进程的View：

public View apply(Context context, ViewGroup parent, OnClickHandler handler) {
    RemoteViews rvToApply = getRemoteViewsToApply(context);
    View result = inflateView(context, rvToApply, parent);
    loadTransitionOverride(context, handler);
    rvToApply.performApply(result, parent, handler);
    return result;
}

先获得RemoteViews，然后调用inflateView方法获取视图View，inflateView方法如下：

private View inflateView(Context context, RemoteViews rv, ViewGroup parent) {
    // RemoteViews may be built by an application installed in another
    // user. So build a context that loads resources from that user but
    // still returns the current users userId so settings like data / time formats
    // are loaded without requiring cross user persmissions.
    final Context contextForResources = getContextForResources(context);
    Context inflationContext = new RemoteViewsContextWrapper(context, contextForResources);

    // If mApplyThemeResId is not given, Theme.DeviceDefault will be used.
    if (mApplyThemeResId != 0) {
        inflationContext = new ContextThemeWrapper(inflationContext, mApplyThemeResId);
    }
    LayoutInflater inflater = (LayoutInflater)
            context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

    // Clone inflater so we load resources from correct context and
    // we don't add a filter to the static version returned by getSystemService.
    inflater = inflater.cloneInContext(inflationContext);
    inflater.setFilter(this);
    View v = inflater.inflate(rv.getLayoutId(), parent, false);
    v.setTagInternal(R.id.widget_frame, rv.getLayoutId());
    return v;
}

通过getLayoutId()获取layoutId：

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public int getLayoutId() {
    return mLayoutId;
}

在RemoteViews中的apply方法中有一个performApply方法，该方法源码如下：

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);
            a.apply(v, parent, handler);
        }
    }
}

该方法会遍历每一个Action并调用对应action的apply方法，对View进行更新处理，而该apply方法是属于Action类的抽象方法：

1	public abstract void apply(View root, ViewGroup rootParent,OnClickHandler handler) throws ActionException;

而该Action有很多用于操作View的子类，例如操作Text的ReflectionAction类：

public void setTextViewText(int viewId, CharSequence text) {
    setCharSequence(viewId, "setText", text);
}
public void setCharSequence(int viewId, String methodName, CharSequence value) {
    addAction(new ReflectionAction(viewId, methodName, ReflectionAction.CHAR_SEQUENCE, value));
}

viewId为视图（根据layoutId得出的）中的具体控件id，methodName为方法名（这里是setText），text为要设置的内容，addAction表明每进行一次对远程视图的操作都会封装成一个Action并添加到一个Action容器中，每一个操作都是一个Action的子类，该子类重写了Action的apply方法，并在内部通过反射机制调用View的具体方法，如setText。

通过RemoteViews更新不同线程的UI例子

MainActivity.class:

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Intent intent=new Intent(this,RemoteActivity.class);
        startActivity(intent);
    }
    private void notifyRemote(){
        RemoteViews remoteViews=new RemoteViews(getPackageName(),R.layout.view_notification);
        remoteViews.setTextViewText(R.id.text_notify_custom,"remote");
        Intent intent=new Intent("ACTION_NOTIFY_REMOTE_ACTIVITY");
        intent.putExtra("REMOTE_VIEWS",remoteViews);
        sendBroadcast(intent);
    }

    @Override
    protected void onStop() {
        super.onStop();
        notifyRemote();
    }
}

RemoteActivity.class:

package io.github.grooters.fifth;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.LinearLayout;
import android.widget.RemoteViews;

/**
 * Create by 李林浪 in 2018/12/17
 * Elegant Code...
 */
public class RemoteActivity extends AppCompatActivity {
    private final String TAG="RemoteActivity_debug";
    private LinearLayout content;
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_remote);
        initView();
    }
    private BroadcastReceiver receiver=new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            Log.d(TAG,"onReceive");
            RemoteViews remoteViews=intent.getParcelableExtra("REMOTE_VIEWS");
            updateUI(remoteViews);
        }
    };
    private void updateUI(RemoteViews remoteViews){
        if(remoteViews!=null){
            Log.d(TAG,"remoteViews!=null");
            View view=remoteViews.apply(this,content);
            content.addView(view);
        }
    }
    private void initView(){
        IntentFilter filter=new IntentFilter("ACTION_NOTIFY_REMOTE_ACTIVITY");
        registerReceiver(receiver,filter);
        content=findViewById(R.id.linear_content);
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
        unregisterReceiver(receiver);
    }
}

AndroidManifest.xml:

1	<activity android:name=".RemoteActivity" android:process=":remote"/>

其它RemoteViews的使用还有通知和桌面小部件，具体使用参照：

Android桌面小部件

通知与自定义通知