如何实现与 CrossProcessCursor 兼容的通用自定义 CursorWrapper

Question

I manage to create a working CursorWrapper , but get stuck when I want to use my ContentProvider across processes.

These posts even show how to implement the CrossProcessCursor interface, notably the hard and undocumented fillWindow() method:

• What to do in custom ContentProvider's fillWindow() method?

• Passing binary blob through a content provider

The problem is that I can think only of an implementation of fillWindow() that deals with a cursor with either all columns containing Blobs, or Strings, or..., but not a mix of those , as a real-world cursor is bound to have. The real issue here is a lack of a getType() function (exists only from v11 on), or a getRaw() / putRaw() that would just copy binary without complaining. How do you deal with this without incurring unwanted conversions in your returned cursor values?

Answer 1

I've implemented it as follows for now, but it does not feel like the right thing to do or robust:

/**
 * Copy data from cursor to CursorWindow
 * @param position start position of data
 * @param window
 */
public void fillWindow(int position, CursorWindow window) {
    if (position < 0 || position > getCount()) {
        return;
    }
    window.acquireReference();
    try {
        int oldpos = this.getPosition();
        this.moveToPosition(position - 1);
        window.clear();
        window.setStartPosition(position);
        int columnNum = getColumnCount();
        window.setNumColumns(columnNum);
        while (moveToNext() && window.allocRow()) {            
            for (int i = 0; i < columnNum; i++) {

                //int type = getType(i);//only from v11 on

                try {
                    String field7 = getString(i);
                    if (field7 != null) {
                        try {
                                if (!window.putLong(new Long(field7), this.getPosition(), i)) {
                                    if (!window.putDouble(new Double(field7), this.getPosition(), i)) {
                                        if (!window.putString(field7, this.getPosition(), i)) {
                                            window.freeLastRow();
                                            break;
                                        }
                                    }
                                }
                            } catch (NumberFormatException e) {
                                try {
                                    if (!window.putDouble(new Double(field7), this.getPosition(), i)) {
                                        if (!window.putString(field7, this.getPosition(), i)) {
                                            window.freeLastRow();
                                            break;
                                        }
                                    }
                                } catch (NumberFormatException e1) {
                                    if (!window.putString(field7, this.getPosition(), i)) {
                                        window.freeLastRow();
                                        break;
                                    }
                                }
                            }
                    } else {
                        if (!window.putNull(this.getPosition(), i)) {
                            window.freeLastRow();
                            break;
                        }
                    }
                } catch (SQLiteException e7) {

                    try {
                        byte[] field1 = getBlob(i);
                        if (field1 != null) {
                            if (!window.putBlob(field1, this.getPosition(), i)) {
                                window.freeLastRow();
                                break;
                            }
                        } else {
                            if (!window.putNull(this.getPosition(), i)) {
                                window.freeLastRow();
                                break;
                            }
                        }
                    } catch (SQLiteException e1) {
                        throw e1;
                    }
                }
            }
        }

        this.moveToPosition(oldpos);
    } catch (IllegalStateException e){
        // simply ignore it
    } finally {
        window.releaseReference();
    }
}