add vpn component detect

app/src/main/java/com/github/kr328/clash/MainActivity.kt

@@ -35,8 +35,15 @@ class MainActivity : BaseActivity() {
                 stopClashService()
             } else {
                 val vpnRequest = startClashService()
-                if (vpnRequest != null)
-                    startActivityForResult(vpnRequest, REQUEST_CODE)
+                if (vpnRequest != null) {
+                    val resolved = packageManager.resolveActivity(vpnRequest, 0)
+                    if ( resolved != null ) {
+                        startActivityForResult(vpnRequest, REQUEST_CODE)
+                    }
+                    else {
+                        makeSnackbarException(getString(R.string.missing_vpn_component), null)
+                    }
+                }
             }
         }
 

app/src/main/res/values-zh/strings.xml

@@ -130,4 +130,5 @@
     <string name="learn_more_about_split_apks">了解更多关于分包机制</string>
     <string name="reinstall_from_google_play">重新从 Google Play 安装</string>
     <string name="download_from_github_releases">从 Github Release 下载</string>
+    <string name="missing_vpn_component">系统 VPN 组件缺失</string>
 </resources>

app/src/main/res/values/strings.xml

@@ -172,4 +172,5 @@
     <string name="github_releases_url" translatable="false">https://github.com/Kr328/ClashForAndroid/releases</string>
 
     <string name="format_proxy_group_title" translatable="false">%s - %s</string>
+    <string name="missing_vpn_component">Missing VPN Components</string>
 </resources>