When you are using React components you need to be able to access specific references to individual components. This is done by defining a ref . ! DOCTYPE html html head lang ="en" meta charset ="UTF-8" title React Lesson 5: Using Refs to
When you are using React components you need to be able to access specific references to individual components. This is done by defining a ref
.
<span><span>DOCTYPE html</span><span>></span> <span><span>html</span><span>></span> <span><span>head </span><span>lang</span><span>="en"</span><span>></span> <span><span>meta </span><span>charset</span><span>="UTF-8"</span><span>></span> <span><span>title</span><span>></span>React Lesson 5: Using Refs to Access Components<span></span><span>title</span><span>></span> <span></span><span>head</span><span>></span> <span><span>body</span><span>></span> <span><span>script </span><span>src</span><span>="https://cdnjs.cloudflare.com/ajax/libs/react/0.12.2/react.js"</span><span>></span><span>script</span><span>></span> <span><span>script </span><span>src</span><span>="https://cdnjs.cloudflare.com/ajax/libs/react/0.12.2/JSXTransformer.js"</span><span>></span><span>script</span><span>></span> <span><span>script </span><span>type</span><span>="text/jsx"</span><span>></span> <span>var</span><span> React_app </span><span>=</span><span> React.createClass({ getInitialState: </span><span>function</span><span>() { </span><span>return</span><span> { red: </span><span>128</span><span>, green: </span><span>128</span><span>, blue: </span><span>128</span><span> } }, myUpdate: </span><span>function</span><span>(){ </span><span>this</span><span>.setState({ red: </span><span>this</span><span>.refs.red.getDOMNode().value, green: </span><span>this</span><span>.refs.green.getDOMNode().value, blue: </span><span>this</span><span>.refs.blue.getDOMNode().value }); }, render: </span><span>function</span><span>() { </span><span>return</span><span> ( </span><span><span>div</span><span>></span> <span><span>Silder update</span><span>=</span><span>{</span><span>this</span><span>.myUpdate} ref</span><span>=</span><span>"</span><span>red</span><span>"</span><span>><span>/</span><span>Silder><label>{this.state.red}<span>/</span><span>label</span><span>><span>br</span><span>/</span><span>></span> <span><span>Silder update</span><span>=</span><span>{</span><span>this</span><span>.myUpdate} ref</span><span>=</span><span>"</span><span>green</span><span>"</span><span>><span>/</span><span>Silder><label>{this.state.green}<span>/</span><span>label</span><span>><span>br</span><span>/</span><span>></span> <span><span>Silder update</span><span>=</span><span>{</span><span>this</span><span>.myUpdate} ref</span><span>=</span><span>"</span><span>blue</span><span>"</span><span>><span>/</span><span>Silder><label>{this.state.blue}<span>/</span><span>label</span><span>><span>br</span><span>/</span><span>></span> <span><span>/</span><span>div></span> <span> ); } }); </span><span>var</span><span> Silder </span><span>=</span><span> React.createClass({ render: </span><span>function</span><span>(){ </span><span>return</span><span> ( </span><span><span>input type</span><span>=</span><span>"</span><span>range</span><span>"</span><span> min</span><span>=</span><span>"</span><span>0</span><span>"</span><span> max</span><span>=</span><span>"</span><span>255</span><span>"</span><span> onChange</span><span>=</span><span>{</span><span>this</span><span>.props.update}</span><span>/</span><span>></span> <span> ) } }); React.render(</span><span><span>React_app </span><span>/</span><span>>, document.body);</span> <span></span><span>script</span><span>></span> <span></span><span>body</span><span>></span> <span></span><span>html</span><span>></span></span></span></span></span></label></span></span></span></span></label></span></span></span></span></label></span></span></span></span></span></span></span></span></span></span></span></span></span>
Here we use getDOMNode() to get the html node:
<span><span>Silder </span><span>update</span><span>={this.myUpdate} </span><span>ref</span><span>="red"</span><span>></span><span>Silder</span><span>></span></span>
then get value from it:
this.refs.red.getDOMNode().value
But, if we add a div:
<span> var Silder = React.createClass({ render: function(){ return ( </span><span><span>div</span><span>></span> <span><!--</span><span> added </span><span>--></span> <span><span>input </span><span>type</span><span>="range"</span><span> min</span><span>="0"</span><span> max</span><span>="255"</span><span> onChange</span><span>={this.props.update}</span><span>/></span> <span></span><span>div</span><span>></span> <span><!--</span><span> added </span><span>--></span><span> ) } });</span></span></span>
We found it doesn't work.
The way can solve this problem is by adding another ref to the input element:
<span> var Silder = React.createClass({ render: function(){ return ( </span><span><span>div </span><span>></span> <span><span>input </span><span>type</span><span>="range"</span><span> min</span><span>="0"</span><span> max</span><span>="255"</span><span> ref</span><span>="range"</span><span> onChange</span><span>={this.props.update}</span><span>/></span> <span></span><span>div</span><span>></span><span> ) } });</span></span></span>
myUpdate: <span>function</span><span>(){ </span><span>this</span><span>.setState({ red: </span><span>this</span><span>.refs.red.refs.range.getDOMNode().value, green: </span><span>this</span><span>.refs.green.refs.range.getDOMNode().value, blue: </span><span>this</span><span>.refs.blue.refs.range.getDOMNode().value }); },</span>

MySQL和SQLite的主要區別在於設計理念和使用場景:1.MySQL適用於大型應用和企業級解決方案,支持高性能和高並發;2.SQLite適合移動應用和桌面軟件,輕量級且易於嵌入。

MySQL中的索引是數據庫表中一列或多列的有序結構,用於加速數據檢索。 1)索引通過減少掃描數據量提升查詢速度。 2)B-Tree索引利用平衡樹結構,適合範圍查詢和排序。 3)創建索引使用CREATEINDEX語句,如CREATEINDEXidx_customer_idONorders(customer_id)。 4)複合索引可優化多列查詢,如CREATEINDEXidx_customer_orderONorders(customer_id,order_date)。 5)使用EXPLAIN分析查詢計劃,避

在MySQL中使用事務可以確保數據一致性。 1)通過STARTTRANSACTION開始事務,執行SQL操作後用COMMIT提交或ROLLBACK回滾。 2)使用SAVEPOINT可以設置保存點,允許部分回滾。 3)性能優化建議包括縮短事務時間、避免大規模查詢和合理使用隔離級別。

選擇PostgreSQL而非MySQL的場景包括:1)需要復雜查詢和高級SQL功能,2)要求嚴格的數據完整性和ACID遵從性,3)需要高級空間功能,4)處理大數據集時需要高性能。 PostgreSQL在這些方面表現出色,適合需要復雜數據處理和高數據完整性的項目。

MySQL數據庫的安全可以通過以下措施實現:1.用戶權限管理:通過CREATEUSER和GRANT命令嚴格控制訪問權限。 2.加密傳輸:配置SSL/TLS確保數據傳輸安全。 3.數據庫備份和恢復:使用mysqldump或mysqlpump定期備份數據。 4.高級安全策略:使用防火牆限制訪問,並啟用審計日誌記錄操作。 5.性能優化與最佳實踐:通過索引和查詢優化以及定期維護兼顧安全和性能。

如何有效監控MySQL性能?使用mysqladmin、SHOWGLOBALSTATUS、PerconaMonitoringandManagement(PMM)和MySQLEnterpriseMonitor等工具。 1.使用mysqladmin查看連接數。 2.用SHOWGLOBALSTATUS查看查詢數。 3.PMM提供詳細性能數據和圖形化界面。 4.MySQLEnterpriseMonitor提供豐富的監控功能和報警機制。

MySQL和SQLServer的区别在于:1)MySQL是开源的,适用于Web和嵌入式系统,2)SQLServer是微软的商业产品,适用于企业级应用。两者在存储引擎、性能优化和应用场景上有显著差异,选择时需考虑项目规模和未来扩展性。

在需要高可用性、高級安全性和良好集成性的企業級應用場景下,應選擇SQLServer而不是MySQL。 1)SQLServer提供企業級功能,如高可用性和高級安全性。 2)它與微軟生態系統如VisualStudio和PowerBI緊密集成。 3)SQLServer在性能優化方面表現出色,支持內存優化表和列存儲索引。


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