Foreword:
When using Windows 10, you often encounter some software prompts: "The applications on your computer need to use the following Windows features: .NET Framework 3.5 (including .NET 2.0 and 3.0)", and click "Download and install this feature" Finally, you need to download and install it online through Windows Update, which is very slow, so let’s talk about how to install .NET Framework 3.5 offline.
method:
1. Prepare a Windows 10 ISO image file, then right-click and select "Mount". 
2. After loading, the virtual optical drive "DVD drive (K:)" just loaded will be displayed in "This Computer". Record this drive letter as "K", which will be used later. (The drive letter may not be "K" according to your actual situation)
3. Run the "Command Prompt" as an administrator (click the Windows icon, find "Windows System", right-click and select "More", and then click " Run as administrator") or right-click the Windows icon and select "Windows PowerShell (Administrator)" to execute the following command:
dism.exe /online /enable-feature /featurename:netfx3 /Source:K:\sources\sxs
注意：其中的盘符K要改成你自己装载ISO镜像文件后实际的虚拟光驱盘符。
After executing the command, wait for the deployment progress to reach 100% and prompt "The operation was completed successfully", which means that the installation of .NET Framework 3.5 for Windows 10 system has been completed.
4. Open the Control Panel, enter "Programs", click "Turn Windows features on or off" under "Programs and Features", and then check ".NET Framework 3.5 (including .NET 2.0 and 3.0)" in the "Windows Features" window that opens. )", if it has been selected, it proves that the installation has been successful.
Other methods:
-method 1:
You can download the .Net Framework 3.5 offline installation package below for installation.
32+64-bit .Net Framework 3.5 SP1 offline installation package download address:
-Method 2:
First put the downloaded offline installation package named NetFx3.cab into the C:\Windows folder of the Win10 system disk, then run the command prompt as an administrator, enter and press Enter to run the following command:
dism /online /Enable-Feature /FeatureName:NetFx3 /Source:"%windir%" /LimitAccess
Just wait for the deployment progress to be 100%.
-Method 3:
Please follow these steps:
1. Turn off all anti-virus software and computer management managers such as 360 Security Guard.
2. Turn on the WINDOWS UPDATE automatic update in the service
3. Close the .NET Framework 4.6 advanced service
4. Download the offline installation package of NetFx3.cab and copy it to the C:\Windows folder of the Win10 system disk.
5. Run "Command Prompt" as an administrator.
6. Paste the command in the pop-up command prompt box: dism.exe /online /add-package /packagepath:C:\WINDOWS\netfx3.cab
7. When you see the progress bar and the word "Release Space", it is successful.
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