if you have installed WeChat on your iPhone but you still catch an exception called "wechat not installed",just add the following code to your info.plist:
<key>LSApplicationQueriesSchemes</key>
<array>
<string>weixin</string>
</array>
<key>NSAppTransportSecurity</key>
<dict>
<key>NSAllowsArbitraryLoads</key>
<true/>
</dict>
Check your signature please.