如何在程序中安装指定apk文件

/**    
         * 安装apk    
         * @param url    
         */    
        private void installApk(){    
                File apkfile = new File(saveFileName);    
                if (!apkfile.exists()) {    
                        return;    
                }            
                Intent i = new Intent(Intent.ACTION_VIEW);    
                i.setDataAndType(Uri.parse("file://" + apkfile.toString()), "application/vnd.android.package-archive");        
                context.startActivity(i);    
        }