Forms, being very utilitarian, vary greatly between iOS and Android to ensure a familiar experience that feels native to each platform.
Checkboxes allow the member to select multiple options from a set.
Single Item Select
Single checkmarks allow the member to select one option from a set. Use these only if you think that the member needs to see all available options side-by-side.
Most field should be able to fit the label on the left and the field entry (or placeholder text) on the right. These type of fields can be used with keyboards, number keyboards and pickers.
When the member has entered or made a selection the field changes into a complete state where the detail text changes to #gray1 to show completion.
Errors / Warnings
Default Field with Pickers
Use pickers when you have a finite set of choices the member can choose from. Once the member selects an option, show a summary of their choice so it fits in the field.