检测程序是不是被下载过在市场上

try {         PackageManager manager = context.getPackageManager();          PackageInfo appInfo = manager.getPackageInfo(             YOUR_PACKAGE_NAME, PackageManager.GET_SIGNATURES);          // Now test if the first signature equals your debug key.         boolean shouldUseTestServer =              appInfo.signatures[0].toCharsString().equals(YOUR_DEBUG_KEY);      } catch (NameNotFoundException e) {         // Expected exception that occurs if the package is not present.     } 

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