convert JSON to contentvalues

问题:

Is there an easy way to get JSON from a webservice and put it into my SQLite DB in C# mono for android (xamarin)? There are some tedious ways to do it but I want something quick and elegant.

回答1:

The question is old, but here is the equivalent code of @gghuffer in Java:

public static ContentValues objectToContentValues(Object o) throws IllegalAccessException {
    ContentValues cv = new ContentValues();

    for (Field field : o.getClass().getFields()) {
        Object value = field.get(o);
        //check if compatible with contentvalues
        if (value instanceof Double || value instanceof Integer || value instanceof R.string || value instanceof Boolean
                || value instanceof Long || value instanceof Float || value instanceof Short) {
            cv.put(field.getName(), value.toString());
            Log.d("CVLOOP", field.getName() + ":" + value.toString());
        } else if (value instanceof Date) {
            cv.put(field.getName(), new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format((Date)value));
        }
    }

    return cv;
}

For use this, you need to use the library of Gson and define java classes for all your json (i.e. 1 object - 1 json), then, for every class, you need to implement the following piece of code:

 public static YourClass fromJSON(String dpJSON) {
        Gson gson = new Gson();
        return gson.fromJson(dpJSON, YourClass.class);
 }

Finally, you have your json string jsonStr, so:

ContentValues cv = Util.objectToContentValues(YourClass.fromJSON(jsonStr));

Hope this helps

回答2:

I made the following class to handle this when using @SerializedName annotations, it also adds support for ignoring certain fields. Hope it helps someone.

import android.content.ContentValues;
import com.google.gson.annotations.SerializedName;

import java.lang.reflect.Field;
import java.util.Arrays;
import java.util.Date;
import java.util.List;

public class ContentValuesWriter {

    public static ContentValues objectToContentValues(Object o, Field... ignoredFields) {
        try {
            ContentValues values = new ContentValues();

            //Will ignore any of the fields you pass in here
            List<Field> fieldsToIgnore = Arrays.asList(ignoredFields);

            for(Field field : o.getClass().getDeclaredFields()) {
                field.setAccessible(true);

                if(fieldsToIgnore.contains(field))
                    continue;

                Object value = field.get(object);
                if(value != null) {
                    //This part just makes sure the content values can handle the field
                    if(value instanceof Double || value instanceof Integer || value instanceof String || value instanceof Boolean
                            || value instanceof Long || value instanceof Float || value instanceof Short) {
                        values.put(field.getAnnotation(SerializedName.class).value(), value.toString());
                    }
                    else if (value instanceof Date)
                        values.put(field.getName(), Constants.DATE_FORMAT_FULL.format((Date) value));
                    else
                        throw new IllegalArgumentException("value could not be handled by field: " + value.toString());
                }
                else
                    Print.log("value is null, so we don't include it");
            }

            return values;
        } catch(Exception e) {
            Print.exception(e);
            throw new NullPointerException("content values failed to build");
        }
    }

}

You'll need to replace a few things there which are custom to my app, just the date format and Print function.

回答3:

I made a static class that will convert any object into contentvalues using reflection. I'm sure there's an equivalent way to do this in Java. Put your JSON objects into a class of some sort and this will convert all of the properties into contentvalues.

public static class Util
{
    //suck all of the data out of a class and put it into a ContentValues object for use in SQLite Database stuff
    public static ContentValues ReflectToContentValues(object o)
    {
        ContentValues cv = new ContentValues();

        foreach (var props in o.GetType().GetProperties())
        {
            object val = props.GetValue(o, null);
            //check if compatible with contentvalues (sbyte and byte[] are also compatible, but will you ever use them in an SQLite database?
            if (props.CanRead && props.CanWrite && (val is double || val is int || val is string || val is bool || val is long || val is float || val is short))
            {
                cv.Put(props.Name, val.ToString());
                Log.Info("CVLOOP", props.Name + ":" + val.ToString());
            }
            else if (val is DateTime)
                cv.Put(props.Name, ((DateTime)val).ToString("yyyy-MM-dd HH:mm:ss"));
        }

        return cv;
    }

}