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<div class="section" id="trade-offers">
<h1>Trade-Offers<a class="headerlink" href="#trade-offers" title="Permalink to this headline">¶</a></h1>
<p>This topic covers the ingame <a class="reference external" href="https://jd.spongepowered.org/6.0.0/org/spongepowered/api/item/merchant/TradeOffer.html">TradeOffer</a>s offered by <a class="reference external" href="https://jd.spongepowered.org/6.0.0/org/spongepowered/api/entity/living/Villager.html">Villager</a>s/<a class="reference external" href="https://jd.spongepowered.org/6.0.0/org/spongepowered/api/item/merchant/Merchant.html">Merchant</a>s.</p>
<div class="section" id="merchant">
<h2>Merchant<a class="headerlink" href="#merchant" title="Permalink to this headline">¶</a></h2>
<p>A <code class="docutils literal"><span class="pre">Merchant</span></code> is a container for <code class="docutils literal"><span class="pre">TradeOffers</span></code>. Its most common variant is the <code class="docutils literal"><span class="pre">Villager</span></code>.
The <code class="docutils literal"><span class="pre">Merchant</span></code> interface can be used to open trading windows.</p>
<p><code class="docutils literal"><span class="pre">TradeOffers</span></code> can be added to and removed from <code class="docutils literal"><span class="pre">Merchants</span></code> using <a class="reference external" href="https://jd.spongepowered.org/6.0.0/org/spongepowered/api/data/manipulator/mutable/entity/TradeOfferData.html">TradeOfferData</a>.</p>
</div>
<div class="section" id="tradeoffer">
<h2>TradeOffer<a class="headerlink" href="#tradeoffer" title="Permalink to this headline">¶</a></h2>
<p>A trade offer consists of</p>
<ul class="simple">
<li>an primary/first buying <a class="reference external" href="https://jd.spongepowered.org/6.0.0/org/spongepowered/api/item/inventory/ItemStackSnapshot.html">ItemStackSnapshot</a></li>
<li>an optional secondary buying <code class="docutils literal"><span class="pre">ItemStackSnapshot</span></code></li>
<li>a selling <code class="docutils literal"><span class="pre">ItemStackSnapshot</span></code></li>
<li>already used uses</li>
<li>maximal available uses</li>
<li>a flag to indicate whether experience orbs are spawned on trade</li>
</ul>
<p><code class="docutils literal"><span class="pre">TradeOffers</span></code> can be created using a <code class="docutils literal"><span class="pre">Builder</span></code> or a <a class="reference external" href="https://jd.spongepowered.org/6.0.0/org/spongepowered/api/item/merchant/TradeOfferGenerator.html">TradeOfferGenerator</a>.</p>
<div class="section" id="tradeofferbuilder">
<h3>TradeOfferBuilder<a class="headerlink" href="#tradeofferbuilder" title="Permalink to this headline">¶</a></h3>
<p><code class="docutils literal"><span class="pre">TradeOfferBuilders</span></code> are mainly used if you want to dynamically create <code class="docutils literal"><span class="pre">TradeOffers</span></code> on the fly.</p>
<p>The following code block builds a new <code class="docutils literal"><span class="pre">TradeOffer</span></code> that allows <code class="docutils literal"><span class="pre">Players</span></code> to trade five <code class="docutils literal"><span class="pre">DIRT</span></code> into three <code class="docutils literal"><span class="pre">GRASS</span></code>
block items. This trade offer has four initial uses, after that the <code class="docutils literal"><span class="pre">Merchant</span></code> might need some time to offer this
<code class="docutils literal"><span class="pre">TradeOffer</span></code> again.</p>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="n">TradeOffer</span> <span class="n">offer</span> <span class="o">=</span> <span class="n">TradeOffer</span><span class="o">.</span><span class="na">builder</span><span class="o">()</span>
<span class="o">.</span><span class="na">firstBuyingItem</span><span class="o">(</span><span class="n">ItemStack</span><span class="o">.</span><span class="na">of</span><span class="o">(</span><span class="n">ItemTypes</span><span class="o">.</span><span class="na">DIRT</span><span class="o">,</span> <span class="mi">5</span><span class="o">))</span>
<span class="o">.</span><span class="na">sellingItem</span><span class="o">(</span><span class="n">ItemStack</span><span class="o">.</span><span class="na">of</span><span class="o">(</span><span class="n">ItemTypes</span><span class="o">.</span><span class="na">GRASS</span><span class="o">,</span> <span class="mi">3</span><span class="o">))</span>
<span class="o">.</span><span class="na">uses</span><span class="o">(</span><span class="mi">0</span><span class="o">)</span>
<span class="o">.</span><span class="na">maxUses</span><span class="o">(</span><span class="mi">4</span><span class="o">)</span>
<span class="o">.</span><span class="na">canGrantExperience</span><span class="o">(</span><span class="kc">false</span><span class="o">)</span>
<span class="o">.</span><span class="na">build</span><span class="o">();</span>
</pre></div>
</div>
</div>
<div class="section" id="tradeofferlistmutator">
<h3>TradeOfferListMutator<a class="headerlink" href="#tradeofferlistmutator" title="Permalink to this headline">¶</a></h3>
<p>A <a class="reference external" href="https://jd.spongepowered.org/6.0.0/org/spongepowered/api/item/merchant/TradeOfferListMutator.html">TradeOfferListMutator</a> is an interface that is invoked during <code class="docutils literal"><span class="pre">Villager</span></code> level ups.
It can be used to replace existing <code class="docutils literal"><span class="pre">TradeOffers</span></code> (ex higher tier) and add new <code class="docutils literal"><span class="pre">TradeOffers</span></code>.
Its simplist and only API provided variant is the <code class="docutils literal"><span class="pre">TradeOfferGenerator</span></code>.
The different <code class="docutils literal"><span class="pre">TradeOfferListMutators</span></code> for each level and <code class="docutils literal"><span class="pre">Career</span></code> can be configured in the <a class="reference external" href="https://jd.spongepowered.org/6.0.0/org/spongepowered/api/item/merchant/VillagerRegistry.html">VillagerRegistry</a>.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The <code class="docutils literal"><span class="pre">TradeOffer</span></code> list in <code class="docutils literal"><span class="pre">Villagers</span></code> might be generated lazily when the trading inventory is opened for the
first time.</p>
</div>
</div>
<div class="section" id="tradeoffergenerator">
<h3>TradeOfferGenerator<a class="headerlink" href="#tradeoffergenerator" title="Permalink to this headline">¶</a></h3>
<p><code class="docutils literal"><span class="pre">TradeOfferGenerators</span></code> are simple templates for new <code class="docutils literal"><span class="pre">TradeOffers</span></code>. They are a variant of the
<code class="docutils literal"><span class="pre">TradeOfferListMutator</span></code> that will only add new entries and does not alter or remove any existing <code class="docutils literal"><span class="pre">TradeOffers</span></code> on
that villager.</p>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="n">TradeOfferGenerator</span> <span class="n">tradeOfferGenerator</span> <span class="o">=</span> <span class="n">TradeOfferGenerator</span><span class="o">.</span><span class="na">builder</span><span class="o">()</span>
<span class="o">.</span><span class="na">setPrimaryItemGenerator</span><span class="o">(</span><span class="n">random</span> <span class="o">-></span> <span class="n">ItemStack</span><span class="o">.</span><span class="na">of</span><span class="o">(</span><span class="n">ItemTypes</span><span class="o">.</span><span class="na">DIRT</span><span class="o">,</span> <span class="n">random</span><span class="o">.</span><span class="na">nextInt</span><span class="o">(</span><span class="mi">3</span><span class="o">)</span> <span class="o">+</span> <span class="mi">5</span><span class="o">))</span>
<span class="o">.</span><span class="na">setSellingGenerator</span><span class="o">(</span><span class="n">random</span> <span class="o">-></span> <span class="n">ItemStack</span><span class="o">.</span><span class="na">of</span><span class="o">(</span><span class="n">ItemTypes</span><span class="o">.</span><span class="na">GRASS</span><span class="o">,</span> <span class="mi">5</span><span class="o">))</span>
<span class="o">.</span><span class="na">startingUses</span><span class="o">(</span><span class="n">VariableAmount</span><span class="o">.</span><span class="na">baseWithVariance</span><span class="o">(</span><span class="mi">2</span><span class="o">,</span> <span class="mi">1</span><span class="o">))</span>
<span class="o">.</span><span class="na">maxUses</span><span class="o">(</span><span class="n">VariableAmount</span><span class="o">.</span><span class="na">fixed</span><span class="o">(</span><span class="mi">5</span><span class="o">))</span>
<span class="o">.</span><span class="na">experienceChance</span><span class="o">(</span><span class="mf">0.5</span><span class="o">)</span>
<span class="o">.</span><span class="na">build</span><span class="o">();</span>
</pre></div>
</div>
<p>This <code class="docutils literal"><span class="pre">TradeOfferGenerator</span></code> will randomly generate <code class="docutils literal"><span class="pre">TradeOffers</span></code> that will</p>
<ul class="simple">
<li>buy 5-8 <code class="docutils literal"><span class="pre">DIRT</span></code></li>
<li>sell 5 <code class="docutils literal"><span class="pre">GRASS</span></code></li>
<li>has 2-4 remaining initial uses</li>
<li>5 max uses</li>
</ul>
<p>The chance that the generated <code class="docutils literal"><span class="pre">TradeOffer</span></code> will grant experience is 50%.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">You can use <code class="docutils literal"><span class="pre">ItemStackGenerators</span></code> to dynamically apply enchantments or other custom data to the buying and
selling items.</p>
</div>
</div>
</div>
<div class="section" id="villagerregistry">
<h2>VillagerRegistry<a class="headerlink" href="#villagerregistry" title="Permalink to this headline">¶</a></h2>
<p>The <code class="docutils literal"><span class="pre">VillagerRegistry</span></code> can be obtained from the <a class="reference external" href="https://jd.spongepowered.org/6.0.0/org/spongepowered/api/GameRegistry.html">GameRegistry</a>. It will be used to configure the
<code class="docutils literal"><span class="pre">TradeOfferListMutator</span></code> that will be applied on a <code class="docutils literal"><span class="pre">Villager</span></code>‘s level-up .</p>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="n">VillagerRegistry</span> <span class="n">villagerRegistry</span> <span class="o">=</span> <span class="k">this</span><span class="o">.</span><span class="na">game</span><span class="o">.</span><span class="na">getRegistry</span><span class="o">().</span><span class="na">getVillagerRegistry</span><span class="o">();</span>
<span class="n">List</span><span class="o"><</span><span class="n">TradeOfferListMutator</span><span class="o">></span> <span class="n">generators</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ArrayList</span><span class="o"><>(</span><span class="n">villagerRegistry</span><span class="o">.</span><span class="na">getMutatorsForCareer</span><span class="o">(</span><span class="n">Careers</span><span class="o">.</span><span class="na">FARMER</span><span class="o">,</span> <span class="mi">1</span><span class="o">));</span>
<span class="n">generators</span><span class="o">.</span><span class="na">addAll</span><span class="o">(</span><span class="n">additionalFarmerLevel1TradeOffers</span><span class="o">());</span>
<span class="n">villagerRegistry</span><span class="o">.</span><span class="na">setMutators</span><span class="o">(</span><span class="n">Careers</span><span class="o">.</span><span class="na">FARMER</span><span class="o">,</span> <span class="mi">1</span><span class="o">,</span> <span class="n">generators</span><span class="o">);</span>
</pre></div>
</div>
<p>The lowest specifiable level-up mutator is level 1. This is equivalent to a newly spawned <code class="docutils literal"><span class="pre">Villager</span></code>.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Changes to the <code class="docutils literal"><span class="pre">VillagerRegistry</span></code> will be lost on server restart and won’t have any impact on the <code class="docutils literal"><span class="pre">TradeOffers</span></code>
from <code class="docutils literal"><span class="pre">Villagers</span></code> that have levelled up in the past.</p>
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