Android：ContentProvider总结

如何使用contentprovider？

1.新建一个类继承于ContentProvider。
public class BedWatchingProvider extends ContentProvider

2.在AndroidManifest中定义她，并且定义他的authorities

        <provider
            android:name=".BedWatchingProvider"
            android:authorities="com.wenfengtou.bedwatching.bedwatchingprovider"
            android:enabled="true"
            android:exported="true"></provider>

3.新建一个数据库帮助类
private static class DatabaseOpenHelper extends SQLiteOpenHelper

4.定义Uri匹配
匹配bedwatching table
sMatcher.addURI(AUTHORITY, "bedwatching", URI_Bed_Watching);

5.在客户端使用contentResolver去获取

                ContentResolver contentResolver = MainActivity.this.getContentResolver();
                Uri uri = new Uri.Builder().scheme(ContentResolver.SCHEME_CONTENT).authority("com.wenfengtou.bedwatching.bedwatchingprovider")
                        .appendPath("bedwatching").build();
                Cursor cursor = contentResolver.query(uri,null,null,null,null);
                if (cursor.moveToFirst()) {
                    Log.i(TAG,"print " + cursor.getColumnIndex("name") + " " + cursor.getString(cursor.getColumnIndex("name")));
                }

android.database.CursorIndexOutOfBoundsException: Index -1 requested, with a size of 1 怎么解决？

获取到数据库的Cursor后，需要首先移动一个游标。
参考：https://blog.csdn.net/woshixuye/article/details/8260547
https://blog.csdn.net/niuba123456/article/details/42638285

QLiteDatabase: android.database.sqlite.SQLiteConstraintException: UNIQUE constraint failed 怎么解决？

是因为重复写数据导致的。我的代码定义了INTEGER PRIMARY KEY AUTOINCREMENT。这个是主键，主键不能重复先的。例如0写了，不能再次直接写入0。
参考：https://blog.csdn.net/wwzqj/article/details/7801702

FileProvider与ContentProvider的区别？

ContentProvider启动流程

03-29 23:32:30.629  3485  3485 I BedWatchingProvider:   at com.wenfengtou.bedwatching.BedWatchingProvider.onCreate(BedWatchingProvider.java:58)
03-29 23:32:30.629  3485  3485 I BedWatchingProvider:   at android.content.ContentProvider.attachInfo(ContentProvider.java:1748)
03-29 23:32:30.629  3485  3485 I BedWatchingProvider:   at android.content.ContentProvider.attachInfo(ContentProvider.java:1723)
03-29 23:32:30.629  3485  3485 I BedWatchingProvider:   at android.app.ActivityThread.installProvider(ActivityThread.java:5153)
03-29 23:32:30.629  3485  3485 I BedWatchingProvider:   at android.app.ActivityThread.installContentProviders(ActivityThread.java:4748)
03-29 23:32:30.629  3485  3485 I BedWatchingProvider:   at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4688)
03-29 23:32:30.629  3485  3485 I BedWatchingProvider:   at android.app.ActivityThread.-wrap1(ActivityThread.java)

publishContentProviders做了什么？

在system_server进程生成一个hash变量mProviderMap，key是authority，value是ContentProviderRecord

ContentResolver查找流程？

确认与AMS进行binder通信的实体先，首先我们可以确认客户端和服务端的接口都是IContentProvider,这个类定义了客户端和服务端通用的接口，其实我们看哪个类继承与IInterface，就知道它是一个binder接口。

public interface IContentProvider extends IInterface {
    public Cursor query(String callingPkg, Uri url, String[] projection, String selection,
            String[] selectionArgs, String sortOrder, ICancellationSignal cancellationSignal)
                    throws RemoteException;
    public String getType(Uri url) throws RemoteException;
    public Uri insert(String callingPkg, Uri url, ContentValues initialValues)
            throws RemoteException;
    public int bulkInsert(String callingPkg, Uri url, ContentValues[] initialValues)
            throws RemoteException;
    public int delete(String callingPkg, Uri url, String selection, String[] selectionArgs)
            throws RemoteException;
    public int update(String callingPkg, Uri url, ContentValues values, String selection,
            String[] selectionArgs) throws RemoteException;
    public ParcelFileDescriptor openFile(
            String callingPkg, Uri url, String mode, ICancellationSignal signal,
            IBinder callerToken)
            throws RemoteException, FileNotFoundException;
    public AssetFileDescriptor openAssetFile(
            String callingPkg, Uri url, String mode, ICancellationSignal signal)
            throws RemoteException, FileNotFoundException;
    public ContentProviderResult[] applyBatch(String callingPkg,
            ArrayList<ContentProviderOperation> operations)
                    throws RemoteException, OperationApplicationException;
    public Bundle call(
            String callingPkg, String method, @Nullable String arg, @Nullable Bundle extras)
            throws RemoteException;
    public ICancellationSignal createCancellationSignal() throws RemoteException;

    public Uri canonicalize(String callingPkg, Uri uri) throws RemoteException;
    public Uri uncanonicalize(String callingPkg, Uri uri) throws RemoteException;

    // Data interchange.
    public String[] getStreamTypes(Uri url, String mimeTypeFilter) throws RemoteException;
    public AssetFileDescriptor openTypedAssetFile(String callingPkg, Uri url, String mimeType,
            Bundle opts, ICancellationSignal signal) throws RemoteException, FileNotFoundException;

    /* IPC constants */
    static final String descriptor = "android.content.IContentProvider";

    static final int QUERY_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION;
    static final int GET_TYPE_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION + 1;
    static final int INSERT_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION + 2;
    static final int DELETE_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION + 3;
    static final int UPDATE_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION + 9;
    static final int BULK_INSERT_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION + 12;
    static final int OPEN_FILE_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION + 13;
    static final int OPEN_ASSET_FILE_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION + 14;
    static final int APPLY_BATCH_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION + 19;
    static final int CALL_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION + 20;
    static final int GET_STREAM_TYPES_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION + 21;
    static final int OPEN_TYPED_ASSET_FILE_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION + 22;
    static final int CREATE_CANCELATION_SIGNAL_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION + 23;
    static final int CANONICALIZE_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION + 24;
    static final int UNCANONICALIZE_TRANSACTION = IBinder.FIRST_CALL_TRANSACTION + 25;
}

谁实现这个接口就是binder实体,所以ContentProviderNative就是binder实体，但是它是抽象的，所以不能实例化，肯定有一个类继承与它，作为最终的binder实体。

abstract public class ContentProviderNative extends Binder implements IContentProvider {

这个最终的类就是Transport,为什么要中间搞一个抽象类呢？是类Transport还扩充了额外的功能，例如权限限制等。

class Transport extends ContentProviderNative {

ContentProvider如何自定义权限？

在AndroidManifest中定义

    <permission android:name="com.wenfengtou.bedwatching.permission.READ_PROVIDER"
        android:protectionLevel="normal" />


        <provider
            android:name=".BedWatchingProvider"
            android:authorities="com.wenfengtou.bedwatching.bedwatchingprovider"
            android:enabled="true"
            android:exported="true"
            android:permission="com.wenfengtou.bedwatching.permission.READ_PROVIDER"></provider>

如何获取contentprovider的应用没有申请这个权限就会报错

03-31 20:58:05.226  8733  8733 E AndroidRuntime: Caused by: java.lang.SecurityException: Permission Denial: opening provider com.wenfengtou.bedwatching.BedWatchingProvider from ProcessRecord{bda6cd8 8733:com.example.wenfengtou.myapplication/u0a60} (pid=8733, uid=10060) requires com.wenfengtou.bedwatching.permission.READ_PROVIDER or com.wenfengtou.bedwatching.permission.READ_PROVIDER
03-31 20:58:05.226  8733  8733 E AndroidRuntime:    at android.os.Parcel.readException(Parcel.java:1599)
03-31 20:58:05.226  8733  8733 E AndroidRuntime:    at android.os.Parcel.readException(Parcel.java:1552)
03-31 20:58:05.226  8733  8733 E AndroidRuntime:    at android.app.ActivityManagerProxy.getContentProvider(ActivityManagerNative.java:3550)
03-31 20:58:05.226  8733  8733 E AndroidRuntime:    at android.app.ActivityThread.acquireProvider(ActivityThread.java:4778)
03-31 20:58:05.226  8733  8733 E AndroidRuntime:    at android.app.ContextImpl$ApplicationContentResolver.acquireUnstableProvider(ContextImpl.java:2018)
03-31 20:58:05.226  8733  8733 E AndroidRuntime:    at android.content.ContentResolver.acquireUnstableProvider(ContentResolver.java:1468)
03-31 20:58:05.226  8733  8733 E AndroidRuntime:    at android.content.ContentResolver.query(ContentResolver.java:475)
03-31 20:58:05.226  8733  8733 E AndroidRuntime:    at android.content.ContentResolver.query(ContentResolver.java:434)
03-31 20:58:05.226  8733  8733 E AndroidRuntime:    at com.example.wenfengtou.myapplication.MainActivity.onResume(MainActivity.java:34)
03-31 20:58:05.226  8733  8733 E AndroidRuntime:    at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1258)
03-31 20:58:05.226  8733  8733 E AndroidRuntime:    at android.app.Activity.performResume(Activity.java:6312)
03-31 20:58:05.226  8733  8733 E AndroidRuntime:    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3092)

这个定位源码是在AMS中函数
getContentProviderImpl － checkContentProviderPermissionLocked

除了这个地方拦截权限，还有另一个地方
/frameworks/base/core/java/android/content/ContentProvider.java
enforceReadPermissionInner
这个函数是跑在ContentProvider进程中的。

ContentProvider的数据是如何传递的？

public interface IBulkCursor extends IInterface

public final class CursorToBulkCursorAdaptor extends BulkCursorNative


/frameworks/base/core/java/android/content/ContentProviderNative.java

                case QUERY_TRANSACTION:
                {
                    data.enforceInterface(IContentProvider.descriptor);

                    String callingPkg = data.readString();
                    Uri url = Uri.CREATOR.createFromParcel(data);

                    // String[] projection
                    int num = data.readInt();
                    String[] projection = null;
                    if (num > 0) {
                        projection = new String[num];
                        for (int i = 0; i < num; i++) {
                            projection[i] = data.readString();
                        }
                    }

                    Bundle queryArgs = data.readBundle();
                    IContentObserver observer = IContentObserver.Stub.asInterface(
                            data.readStrongBinder());
                    ICancellationSignal cancellationSignal = ICancellationSignal.Stub.asInterface(
                            data.readStrongBinder());

                    Cursor cursor = query(callingPkg, url, projection, queryArgs, cancellationSignal);
                    if (cursor != null) {
                        CursorToBulkCursorAdaptor adaptor = null;

                        try {
                            adaptor = new CursorToBulkCursorAdaptor(cursor, observer,
                                    getProviderName());
                            cursor = null;

                            BulkCursorDescriptor d = adaptor.getBulkCursorDescriptor();
                            adaptor = null;

                            reply.writeNoException();
                            reply.writeInt(1);
                            d.writeToParcel(reply, Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
                        } finally {
                            // Close cursor if an exception was thrown while constructing the adaptor.
                            if (adaptor != null) {
                                adaptor.close();
                            }
                            if (cursor != null) {
                                cursor.close();
                            }
                        }
                    } else {
                        reply.writeNoException();
                        reply.writeInt(0);
                    }

                    return true;
                }

创建共享内存的代码如下
/frameworks/base/libs/androidfw/CursorWindow.cpp

CursorWindow::CursorWindow(const String8& name, int ashmemFd,
        void* data, size_t size, bool readOnly) :
        mName(name), mAshmemFd(ashmemFd), mData(data), mSize(size), mReadOnly(readOnly) {
    mHeader = static_cast<Header*>(mData);
}


status_t CursorWindow::create(const String8& name, size_t size, CursorWindow** outCursorWindow) {
    String8 ashmemName("CursorWindow: ");
    ashmemName.append(name);

    status_t result;
    int ashmemFd = ashmem_create_region(ashmemName.string(), size);  //这里创建了共享内存
    if (ashmemFd < 0) {
        result = -errno;
    } else {
        result = ashmem_set_prot_region(ashmemFd, PROT_READ | PROT_WRITE);
        if (result >= 0) {
            void* data = ::mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, ashmemFd, 0);
            if (data == MAP_FAILED) {
                result = -errno;
            } else {
                result = ashmem_set_prot_region(ashmemFd, PROT_READ);
                if (result >= 0) {
                    CursorWindow* window = new CursorWindow(name, ashmemFd,
                            data, size, false /*readOnly*/);
                    result = window->clear();
                    if (!result) {
                        LOG_WINDOW("Created new CursorWindow: freeOffset=%d, "
                                "numRows=%d, numColumns=%d, mSize=%d, mData=%p",
                                window->mHeader->freeOffset,
                                window->mHeader->numRows,
                                window->mHeader->numColumns,
                                window->mSize, window->mData);
                        *outCursorWindow = window;
                        return OK;
                    }
                    delete window;
                }
            }
            ::munmap(data, size);
        }
        ::close(ashmemFd);
    }
    *outCursorWindow = NULL;
    return result;
}

参考：https://blog.csdn.net/new_abc/article/details/8167973

ContentProvider的权限怎么控制？

1.设置android:readPermission，设置android:writePermission
2.设置path-permission，注意android:readPermission的优先级高于path-permission，即如果客户端已经有android:readPermission的权限，则不检验path-permission。如果不满足android:readPermission的权限，则会再看path-permission是否满足。
参考
http://androidxref.com/6.0.0_r1/xref/packages/providers/DownloadProvider/AndroidManifest.xml#72

checkHoldingPermissionsLocked这个对于uri临时授权关键。
ams检查是用checkUriPermission

FileProvider是什么？

FileProvider继承与ContentProvider，用Content：//代替原来的file：//。