UE4下载与存储图片

UE4 从网络端下载图片并且缓存到本地

从网络端下载一个图片，并且在UI上显示出来，然后再缓存到本地文件中，方便下次使用。

下载图片

UE4官方提供了一个异步任务类，专门处理下载图片的需求。

DECLARE_DYNAMIC_MULTICAST_DELEGATE_OneParam(FDownloadImageDelegate, UTexture2DDynamic*, Texture);

UCLASS()
class UMG_API UAsyncTaskDownloadImage : public UBlueprintAsyncActionBase
{
   
	GENERATED_UCLASS_BODY()

public:
	UFUNCTION(BlueprintCallable, meta=( BlueprintInternalUseOnly="true" ))
	static UAsyncTaskDownloadImage* DownloadImage(FString URL);

public:

	UPROPERTY(BlueprintAssignable)
	FDownloadImageDelegate OnSuccess;

	UPROPERTY(BlueprintAssignable)
	FDownloadImageDelegate OnFail;

public:

	void Start(FString URL);

private:

	/** Handles image requests coming from the web */
	void HandleImageRequest(FHttpRequestPtr HttpRequest, FHttpResponsePtr HttpResponse, bool bSucceeded);
};

void UAsyncTaskDownloadImage::HandleImageRequest(FHttpRequestPtr HttpRequest, FHttpResponsePtr HttpResponse, bool bSucceeded)
{
   
#if !UE_SERVER

	RemoveFromRoot();

	if ( bSucceeded && HttpResponse.IsValid() && HttpResponse->GetContentLength() > 0 )
	{
   
		IImageWrapperModule& ImageWrapperModule = FModuleManager::LoadModuleChecked<IImageWrapperModule>(FName("ImageWrapper"));
		TSharedPtr<IImageWrapper> ImageWrappers[3] =
		{
   
			ImageWrapperModule.CreateImageWrapper(EImageFormat::PNG),
			ImageWrapperModule.CreateImageWrapper(EImageFormat::JPEG),
			ImageWrapperModule.CreateImageWrapper(EImageFormat::BMP),
		};

		for ( auto ImageWrapper : ImageWrappers )
		{
   
			if ( ImageWrapper.IsValid() && ImageWrapper->SetCompressed(HttpResponse->GetContent().GetData(), HttpResponse->GetContentLength()) )
			{
   
				TArray64<uint8>* RawData = new TArray64<uint8>();
				const ERGBFormat InFormat = ERGBFormat::BGRA;
				if ( ImageWrapper->GetRaw(InFormat, 8, *RawData) )
				{
   
					if ( UTexture2DDynamic* Texture = UTexture2DDynamic::Create(ImageWrapper->GetWidth(), ImageWrapper->GetHeight()) )
					{
   
						Texture->SRGB = true;
						Texture->UpdateResource();

						FTexture2DDynamicResource* TextureResource = static_cast<FTexture2DDynamicResource*>(Texture->Resource);
						if (TextureResource)
						{
   
							ENQUEUE_RENDER_COMMAND(FWriteRawDataToTexture)(
								[TextureResource, RawData](FRHICommandListImmediate& RHICmdList)