UE4 Editor Plugin UI - Progress bar

制作UE4编辑器插件时，可能会遇到非常耗时的任务。如果不想在没有任何提示信息的情况下冻结编辑器窗口，需要添加一个进度条，以便于用户可以跟踪任务的进度，否则用户会认为当前任务可能处于崩溃。

FScopedSlowTask

一个耗时的任务：

// For each folder found in path
for (FString SubFolder : SubFolders)
{
	// Retrieve assets inside this folder
	TArray AssetDatasFromPath = FTools::GetAssetsFromPath(SubFolder);
	// If there isn't any assets
	if (AssetDatasFromPath.Num() == 0)
	{
		// Remove the folder
		AssetRegistryModule.Get().RemovePath(SubFolder);
	}
}

进度条的基本用法：

//定义一个进度条对象，并设置总的进度值
FScopedSlowTask ExplorePathsTask(SelectedPaths.Num(), LOCTEXT("LookingForUnusedAssetsText", "Looking for assets to remove"));
ExplorePathsTask.MakeDialog();
//进度值增加
ExploreFoldersTask.EnterProgressFrame();

完整示例：

FScopedSlowTask ExploreFoldersTask(SubFolders.Num(), LOCTEXT("LookingForUnusedAssetsText", "Looking for assets to remove"));
ExploreFoldersTask.MakeDialog();

// For each folder found in path
for (FString SubFolder : SubFolders)
{
	ExploreFoldersTask.EnterProgressFrame();
	// Retrieve assets inside this folder
	TArray AssetDatasFromPath = FTools::GetAssetsFromPath(SubFolder);
	// If there isn't any assets
	if (AssetDatasFromPath.Num() == 0)
	{
		// Remove the folder
		AssetRegistryModule.Get().RemovePath(SubFolder);
	}
}

对于FScopeSlowTask对象，还可以用于一下情况：

可以嵌套耗时的子任务
可以设置取消当前任务
可以设置任务的进度量

取消当前任务

FScopedSlowTask ExploreFoldersTask(SubFolders.Num(), LOCTEXT("LookingForUnusedAssetsText", "Looking for assets to remove"));
ExploreFoldersTask.MakeDialog(true);  // We display the Cancel button here

for (FString SubFolder : SubFolders)
{
	// We check if the cancel button has been pressed, if so we break the execution of the loop
	if(ExploreFoldersTask.ShouldCancel())
		break;
	ExploreFoldersTask.EnterProgressFrame();
	// Instructions...
}

指定任务的进度

// Here the total amount of work is set to 100.0f
FScopedSlowTask SlowTask(100.0f, LOCTEXT("SlowTaskText", "Slow Task"));
SlowTask.MakeDialog();

// The first task should represent 10% of the time, so it will be 10% of 100.0f i 10.0f
SlowTask.EnterProgressFrame(10.0f);
// Instructions of the first task...

// The second one should represent 35% of the total time
SlowTask.EnterProgressFrame(35.0f);
// Instructions of the second task...

// The third and last one will be the rest
SlowTask.EnterProgressFrame(55.0f);
// Instructions of the last task...