Fragment的正确使用方式

fragment是我们经常使用到的一个控件，但是，相信大家会出现这样的一个问题，每次切换fragment的时候，fragment就会重新调用一次生命周期的方法，从而会重新加载一次数据，这样既消耗用户的数据流量和机器性能； 现在就教大家一个方法，来解决这个问题； 之前我们一直都是这样写的代码：

<code class="hljs java has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
     * 根据传入的参数来改变当前的fragment
     *
     *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @param</span> fragment
     */</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">showFragment</span>(Fragment fragment) {
        FragmentTransaction transaction = fragmentManager.beginTransaction();
        transaction.replace(R.id.main_fl_content, fragment);
        transaction.commit();
    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

翻看了Android官方文档，发现，replace()这个方法只是在上一个Fragment不再需要使用时采用的简便方法。正确的切换方式是add()，切换时hide()，add()另一个Fragment；再次切换时，只需hide()当前，show()另一个。（这也是谷歌官方推荐的做法）

<code class="hljs java has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"> <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
     * 修改显示的内容 不会重新加载
     * to 下一个fragment
     * mContent 当前的fragment
     */</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">switchContent</span>(Fragment to) {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (mContent != to) {
            FragmentTransaction transaction = fragmentManager
                    .beginTransaction().setCustomAnimations(android.R.anim.fade_in, R.anim.slide_out);
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!to.isAdded()) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 判断是否被add过</span>
                <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 隐藏当前的fragment，将 下一个fragment 添加进去</span>
                transaction.hide(mContent).add(R.id.main_fl_content, to).commit(); 
            } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {
                <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 隐藏当前的fragment，显示下一个fragment</span>
                transaction.hide(mContent).show(to).commit(); 
            }

            mContent = to;
        }

    }</code>