getting data from ID3D11Texture2D - windows-runtime

Question

I saw some similar post but not for NV12 format, so here is my code:
void MyClass::loadPreviewTexture(){
ID3D11Texture2D* textureBuf;
D3D11_TEXTURE2D_DESC textureDesc;
ComPtr<ID3D11Texture2D> tempTexture = this->c_PreviewTexture;
D3D11_TEXTURE2D_DESC tempDesc;
if (tempTexture != nullptr){
tempTexture->GetDesc(&tempDesc);
ComPtr<ID3D11Device> device;
ComPtr<ID3D11DeviceContext> context;
ZeroMemory(&textureDesc, sizeof(textureDesc));
textureDesc.Width = tempDesc.Width;
textureDesc.Height = tempDesc.Height;
textureDesc.MipLevels = tempDesc.MipLevels;
textureDesc.ArraySize = tempDesc.ArraySize;
textureDesc.Format = tempDesc.Format; // NV12
textureDesc.SampleDesc = tempDesc.SampleDesc;
textureDesc.Usage = D3D11_USAGE_STAGING;
textureDesc.CPUAccessFlags = D3D11_CPU_ACCESS_READ;
textureDesc.MiscFlags = tempDesc.MiscFlags;
tempTexture->GetDevice(&device);
device->GetImmediateContext(&context);
device->GetImmediateContext(&context);
device->CreateTexture2D(&textureDesc, NULL, &textureBuf);
context->CopyResource(textureBuf, tempTexture.Get());
D3D11_MAPPED_SUBRESOURCE mapResource;
HRESULT hr = context->Map(textureBuf, 0, D3D11_MAP_READ, NULL, &mapResource);
//data = new byte[(mapResource.RowPitch / sizeof(byte)) * textureDesc.Height];
//this->size = (mapResource.RowPitch / sizeof(byte)) * textureDesc.Height;
this->size = textureDesc.Width * textureDesc.Height * 3 * sizeof(byte);
data = new byte[this->size];
//memcpy(data, mapResource.pData, mapResource.RowPitch* textureDesc.Height);
memcpy(data, mapResource.pData, this->size);
printf("");
}
}
c_PreviewTexture is a ComPtr and contains the data I need.
I'm not sure about the size of data[] and the allocation. The size for NV12 format is suppose to be 1280*720*3 for a resolution of 1280 * 720. I'm missing something because it worked if I copy like this:
memcpy(data, mapResource.pData, mapResource.RowPitch* textureDesc.Height); // 1280*720