android检测手机是否有某个应用以及启动安装另一个应用的问题

/** 
         * 获取所有应用的名称，包名，以及权限 有了包名就可以判断是否有某个应用了 
         */  
        List<PackageInfo> list = getPackageManager().getInstalledPackages(PackageManager.GET_PERMISSIONS);  
          
        StringBuilder stringBuilder = new StringBuilder();  
  
        for (PackageInfo packageInfo : list) {  
             stringBuilder.append("package name:"+ packageInfo.packageName + "\n");  
             ApplicationInfo applicationInfo = packageInfo.applicationInfo;  
             stringBuilder.append("应用名称:"+ applicationInfo.loadLabel(getPackageManager())  
                 + "\n");  
             if (packageInfo.permissions != null) {  
      
                    for (PermissionInfo p : packageInfo.permissions) {  
                     stringBuilder.append("权限包括:" + p.name + "\n");  
                    }  
             }  
             stringBuilder.append("\n");  
        }

// 通过Intent安装APK文件    
    Intent i = new Intent(Intent.ACTION_VIEW);  
    i.setDataAndType(Uri.parse("file://" + apkfile.toString()), "application/vnd.android.package-archive");  
    mContext.startActivity(i);