Android应用之间数据的交互-获取系统应用的数据

在Android应用开发中我们常常需要和其他应用进行交互，之前对这些问题没有仔细了解过，现在来做一下总结。

Android应用之间数据的交互方式：

• 获取系统应用的数据
• 提供数据给其他应用
• 应用之间的分享

下面介绍获取系统应用的数据

实例分析

以获取联系人数据为例，代码如下：

Cursor cursor=getContentResolver().query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI,null,null,null,null);
 if (cursor!=null){
     while(cursor.moveToNext()){
         //获取联系人的名字
         String name=cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME));
         //获取联系人的电话号码
         String number=cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER));
         Log.d("============"," name: "+name+"  number="+number);
     }
     cursor.close();
 }

ContentResolver类的query(Uri uri,String[] projection,String selection,String[] selectionArgs,String sortOrder)方法参数的介绍：

uri用来指明要访问的数据的位置

projection访问的列，如果为null，则表示访问所有列

selection用于指定查询条件

selectionArgs查询参数

sortOrder排序顺序

基本流程

那么ContentResolver是怎么通过query方法来获取联系人的数据的呢？下面我们来分析ContentResolver的源码：

//1
public final @Nullable Cursor query(@RequiresPermission.Read @NonNull Uri uri,
            @Nullable String[] projection, @Nullable String selection,
            @Nullable String[] selectionArgs, @Nullable String sortOrder) {
        return query(uri, projection, selection, selectionArgs, sortOrder, null);
    }
//2
public final @Nullable Cursor query(@RequiresPermission.Read @NonNull Uri uri,
            @Nullable String[] projection, @Nullable String selection,
            @Nullable String[] selectionArgs, @Nullable String sortOrder,
            @Nullable CancellationSignal cancellationSignal) {
        //把查询参数封装在Bundle中
        Bundle queryArgs = createSqlQueryBundle(selection, selectionArgs, sortOrder);
        return query(uri, projection, queryArgs, cancellationSignal);
    }
//3
public final @Nullable Cursor query(final @RequiresPermission.Read @NonNull Uri uri,
            @Nullable String[] projection, @Nullable Bundle queryArgs,
            @Nullable CancellationSignal cancellationSignal) {
        Preconditions.checkNotNull(uri, "uri");
        //获取不稳定的提供者 IContentProvider是IPC接口用来与内容提供者进行数据交互
        IContentProvider unstableProvider = acquireUnstableProvider(uri);
        if (unstableProvider == null) {
            return null;
        }
        IContentProvider stableProvider = null;
        Cursor qCursor = null;
        try {
            ...//省略些不重要的源码
            try {
                qCursor = unstableProvider.query(mPackageName, uri, projection,
                        queryArgs, remoteCancellationSignal);
            } catch (DeadObjectException e) {
                // The remote process has died...  but we only hold an unstable
                // reference though, so we might recover!!!  Let's try!!!!
                // This is exciting!!1!!1!!!!1
                unstableProviderDied(unstableProvider);
                stableProvider = acquireProvider(uri);//第一次创建的是不稳定的，如果失败就重试
                if (stableProvider == null) {
                    return null;
                }
                qCursor = stableProvider.query(
                        mPackageName, uri, projection, queryArgs, remoteCancellationSignal);
            }
            if (qCursor == null) {
                return null;
            }

            // Force query execution.  Might fail and throw a runtime exception here.
            qCursor.getCount();//调用这个方法判断是否查询出错
            long durationMillis = SystemClock.uptimeMillis() - startTime;
            maybeLogQueryToEventLog(durationMillis, uri, projection, queryArgs);

            // Wrap the cursor object into CursorWrapperInner object.
            final IContentProvider provider = (stableProvider != null) ? stableProvider
                    : acquireProvider(uri);
            final CursorWrapperInner wrapper = new CursorWrapperInner(qCursor, provider);//CursorWrapperInner是内部类
            stableProvider = null;
            qCursor = null;
            return wrapper;
        } catch (RemoteException e) {
            // Arbitrary and not worth documenting, as Activity
            // Manager will kill this process shortly anyway.
            return null;
        } finally {//释放资源
           ...
        }
    }
    
    public final IContentProvider acquireUnstableProvider(Uri uri) {
        if (!SCHEME_CONTENT.equals(uri.getScheme())) {//SCHEME_CONTENT为content,如果uri的scheme为null则返回null
            return null;
        }
        String auth = uri.getAuthority();
        if (auth != null) {
            return acquireUnstableProvider(mContext, uri.getAuthority());//这里调用的是ApplicationContentResolver的acquireUnstableProvider方法
        }
        return null;
    }

在ContentResolver的源码中query有三个重载方法1，2，3，在实例中我们调用重载方法1，方法1中则直接调用方法2。在方法2中，封装了数据到Bundle中，并调用了方法3，真正的实现在方法3中。方法3中的核心方法是acquireUnstableProvider(Uri uri),它获取IContentProvider(一个IPC 接口)，并通过IContentProvider来获取联系人的数据。而acquireUnstableProvider(Uri uri)调用的是acquireUnstableProvider(Context c, String name)方法，它是个抽象方法，具体的实现类是ApplicationContentResolver。

ApplicationContentResolver的acquireUnstableProvider方法源码如下：

@Override
protected IContentProvider acquireUnstableProvider(Context c, String auth) {
           return mMainThread.acquireProvider(c,
                 ContentProvider.getAuthorityWithoutUserId(auth),
                 resolveUserIdFromAuthority(auth), false);
      }

在ApplicationContentResolver的acquireUnstableProvider方法调用了ActivityThread的acquireProvider方法，源码如下：

public final IContentProvider acquireProvider(
 Context c, String auth, int userId, boolean stable) {
 // 判断缓存中是否有对应的IContentProvider，有则直接返回
final IContentProvider provider = acquireExistingProvider(c, auth, userId, stable);
       if (provider != null) {
           return provider;
        }
       
        // There is a possible race here.  Another thread may try to acquire
        // the same provider at the same time.  When this happens, we want to ensure
        // that the first one wins.
        // Note that we cannot hold the lock while acquiring and installing the
        // provider since it might take a long time to run and it could also potentially
        // be re-entrant in the case where the provider is in the same process.
        ContentProviderHolder holder = null;
        try {
            //通过AMS获取ContentProviderHolder， 处理在不同进程的情况，
            //如果在同一进程就让`holder.provider = null;`
            holder = ActivityManager.getService().getContentProvider(
                    getApplicationThread(), auth, userId, stable);
        } catch (RemoteException ex) {
            throw ex.rethrowFromSystemServer();
        }
       //失败
       if (holder == null) {
            Slog.e(TAG, "Failed to find provider info for " + auth);
            return null;
        }

        // Install provider will increment the reference count for us, and break
        // any ties in the race.
        //如果在同一进程，则进行相应的处理
        holder = installProvider(c, holder, holder.info,
                true /*noisy*/, holder.noReleaseNeeded, stable);
        return holder.provider;
    }

ApplicationContentResolver通过调用ActivityThread的acquireProvider方法来获取ContentProvider;ActivityThread先会判断缓存中是否存在要求的IContentProvider,
如果存在就直接返回，如果不存在就调用AMS的getContentProviderImpl()和installProvider来获取。

关于AMS获取IContentProvider的详细流程，可以看ContentProvider启动过程分析

ContactsContract详解

ContactsContract是存储联系人的数据表的常量字段，它有几个常用的内部类如下：

• ContactsContract.Data：数据表的常量，包含与原始联系人关联的数据点。 数据表的每一行通常用于存储单条联系信息（例如电话号码）及其相关元数据（例如，它是工作号码还是家庭号码）
• ContactsContract.CommonDataKinds：用于定义存储在ContactsContract.Data表中的公共数据类型的容器。
• ContactsContract.Contacts：联系人表的常量，包含代表同一个人的每个原始联系人聚合的记录

联系人数据是存储在数据库中（具体位置在data/data/com.android.providers.contacts/databases中），根据其MIME类型来判断其位置所代表的意义。如
ContactsContract.CommonDataKinds.Phone.NUMBER和ContactsContract.CommonDataKinds.Email.ADDRESS都表示
data1,但是在数据库中不同的MIME类型的data1表示不同的数据。

数据库中data表的字段和数据如下（字段太多，只截取了部分）

MIME类型如下

通过MIME类型来获取所需要的数据

Uri p = ContactsContract.Data.CONTENT_URI;
Cursor id = getActivity().getContentResolver().query(p,new String[]{ContactsContract.Data.CONTACT_ID},null,null,null);
while (id.moveToNext()){
    Cursor cursor=getActivity().getContentResolver().query(p, null,ContactsContract.Data.CONTACT_ID+"= ?", new String[]{id.getString(id.getColumnIndex(ContactsContract.Data.CONTACT_ID))}, null);
    Person person = new Person();
    byte[] image = null;
    StringBuilder builder = new StringBuilder();
        while (cursor.moveToNext()){
            String mime = cursor.getString(cursor.getColumnIndex(ContactsContract.Data.MIMETYPE));
            Log.d("===========","mime = "+mime);
            if (mime.equals(ContactsContract.CommonDataKinds.Phone.CONTENT_ITEM_TYPE)){
                builder.append("name = "+cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME)));
                builder.append("number = "+cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER)));
            }else if (mime.equals(ContactsContract.CommonDataKinds.Photo.CONTENT_ITEM_TYPE)){
            //二进制数据一般放在data15中
                image=cursor.getBlob(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Photo.DATA15));
            }else if (mime.equals(ContactsContract.CommonDataKinds.Email.CONTENT_ITEM_TYPE)){
                builder.append("email = "+cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Email.ADDRESS)));
            }else if (mime.equals(ContactsContract.CommonDataKinds.StructuredPostal.CONTENT_ITEM_TYPE)){
                builder.append("address = "+cursor.getString(cursor.getColumnIndex(ContactsContract.
                        CommonDataKinds.StructuredPostal.STREET)));
            }
        }
    String con=builder.toString();
    Log.d("===========",con);
    cursor.close();
    }
id.close();

ContentResolver()还有insert、delete、update方法，其用法与query类似，这里不再介绍。

获取其他系统应用数据

CalendarContract

CalendarContract是存储日历和事件相关信息字段表，与ContactsContract类似。CalendarContract也有几个内部类，常用的是CalendarContract.Events，包含诸如事件标题，位置，开始时间，结束时间等信息。CalendarContract.Events的使用如下：

    Uri p = CalendarContract.Events.CONTENT_URI;
    Cursor cursor=getActivity().getContentResolver().query(p, null,null, null, null);
    while (cursor.moveToNext()){
        StringBuilder builder = new StringBuilder();
       builder.append("标题 : "+cursor.getString(cursor.getColumnIndex(CalendarContract.Events.TITLE))+"\n")
               .append("起始时间 ："+cursor.getString(cursor.getColumnIndex(CalendarContract.Events.DTSTART))+"\n")
               .append("结束时间 ："+cursor.getString(cursor.getColumnIndex(CalendarContract.Events.DTEND))+"\n")
               .append("描述 : "+cursor.getString(cursor.getColumnIndex(CalendarContract.Events.DESCRIPTION))+"\n");
        contents.add(builder.toString());
    }
cursor.close();

更多关于CalendarContract的使用，可以查看官方文档。

MediaStore

MediaStore包含内部和外部存储设备上所有可用媒体的元数据。其内部类如下：

• MediaStore.Audio：集装箱所有的音频内容。
• MediaStore.Files：媒体提供程序表，包含媒体存储中所有文件的索引，包括非媒体文件。
• MediaStore.Images：包含所有可用图像的元数据
• interface MediaStore.MediaColumns：大多数MediaProvider表的公共字段
• MediaStore.Video：包含所有可用视频的元数据

List<String> contents = new ArrayList<>();
Uri p1 = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
Cursor cursor1=getActivity().getContentResolver().query(p1, null,null, null, null);
while (cursor1.moveToNext()){
    StringBuilder builder = new StringBuilder();
    builder.append("文件名 : "+cursor1.getString(cursor1.getColumnIndex(MediaStore.Images.Media.TITLE))+"\n")
            .append("描述 ："+cursor1.getString(cursor1.getColumnIndex(MediaStore.Images.Media.DESCRIPTION))+"\n")
            .append("大小 ："+cursor1.getString(cursor1.getColumnIndex(MediaStore.Images.Media.SIZE))+"\n")
            .append("位置 : "+cursor1.getString(cursor1.getColumnIndex(MediaStore.Images.Media.DATA))+"\n")
            .append("文件修改时间："+cursor1.getString(cursor1.getColumnIndex(MediaStore.Images.Media.DATE_MODIFIED))+"\n")
            .append("DISPLAY_NAME ："+cursor1.getString(cursor1.getColumnIndex(MediaStore.Images.Media.DISPLAY_NAME))+"\n")
            .append("时间 : "+cursor1.getString(cursor1.getColumnIndex(MediaStore.Images.Media.DATE_TAKEN))+"\n");
    contents.add(builder.toString());
}
cursor1.close();

Settings

Settings与XXXContract不同，它是通过xml文件来存储数据，在文件/data/system/users/0/目录下，获取设置的方式如下：

StringBuilder builder = new StringBuilder();
        ContentResolver contentResolver=getActivity().getContentResolver();
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
            builder.append("wifi是否开启："+Settings.Global.getString(contentResolver,Settings.Global.WIFI_ON)+"\n")
                   .append("数据流量是否开启："+Settings.Global.getString(contentResolver,Settings.Global.DATA_ROAMING)+"\n")
                   .append(Settings.System.NOTIFICATION_SOUND+" "+Settings.System.getString(contentResolver,Settings.System.NOTIFICATION_SOUND)).append("\n")
                    .append(Settings.System.SCREEN_BRIGHTNESS+" "+Settings.System.getString(contentResolver,Settings.System.SCREEN_BRIGHTNESS)).append("\n")
                    .append(Settings.System.TEXT_SHOW_PASSWORD+" "+Settings.System.getString(contentResolver,Settings.System.TEXT_SHOW_PASSWORD)).append("\n");
        }
        Log.d("==============",builder.toString());

更多关于Setting的内容可以看Android系统APP之SettingsProvider

注意：以上的操作都是需要申请权限的

异步处理

如果请求数据的操作太过耗时，可能造成ANR，因此需要异步处理。异步处理的方式有：

• Thread + Handler
• AsyncTask
• Loader
• RxJava

参考文章：

• https://juejin.im/entry/5bfcf8566fb9a049ba414362
• https://blog.csdn.net/myfriend0/article/details/59107989