private boolean isAvilible(Context context, String packageName){           final PackageManager packageManager = context.getPackageManager();//获取packagemanager           List< packageInfo> pinfo = packageManager.getInstalledPackages(0);//获取所有已安装程序的包信息           List<String> pName = new ArrayList<String>();//用于存储所有已安装程序的包名          //从pinfo中将包名字逐一取出，压入pName list中               if(pinfo != null){               for(int i = 0; i < pinfo.size(); i++){                   String pn = pinfo.get(i).packageName;                   pName.add(pn);               }           }           return pName.contains(packageName);//判断pName中是否有目标程序的包名，有TRUE，没有FALSE     } 

//已安装，打开程序，需传入参数包名："com.tencent.mm" if(isAvilible(this, "com.skype.android.verizon")){                 Intent i = new Intent();                 ComponentName cn = new ComponentName("com.tencent.mm",                         "com.tencent.mm.WeiXinActivity");                 i.setComponent(cn);                 startActivityForResult(i, RESULT_OK);                } //未安装，跳转至market下载该程序 else {       Uri uri = Uri.parse("market://details?id=com.tencent.mm");//id为包名

　　　　// 直接从指定网址下载
      // Uri uri = Uri.parse("http://dldir1.qq.com/foxmail/weixin521android400.apk");
       Intent it = new Intent(Intent.ACTION_VIEW, uri);       startActivity(it);       }