我正在使用GWT Activities and Places框架来组织我的应用程序,结果非常不错。但有一件事情让我很烦恼,ActivityMapper
实现会(1)接收所有应用程序中的视图 (2) 包含一个庞大的if/else块,根据所接收到的位置实例化活动。随着视图数量的增加,这种情况只会变得更糟。
我已经在使用Gin,但是我不知道如何在这里使用它。
如何减少或消除我的ActivityMapper
的样板代码?
class BasePlace extends Place {
<T> T acceptFilter(PlaceFilter filter);
}
interface PlaceFilter<T> {
T filter(FooPlace place);
T filter(BarPlace place);
T filter(BazPlace place);
}
public class MainActivities implements ActivityMapper {
@Inject FooFactory fooMaker;
@Inject BarFactory barMaker;
@Inject BazFactory bazMaker;
public Activity getActivity(PlaceChangeEvent e) {
return ((BasePlace)e.getPlace()).acceptFilter(
new PlaceFilter<Activity>() {
Activity filter(FooPlace place) {
return fooMaker.create(place);
}
Activity filter(BarPlace place) {
return barMaker.create(place);
}
Activity filter(BazPlace place) {
return bazMaker.create(place);
}
})
}
}
一种可能的方法是让您的Place类层次结构的根定义一个createActivity()方法,而Place子类可以返回与其关联的Activity的新实例。
@Override
public Activity getActivity(Place place) {
return ((BaseAppPlace)place).createActivity();
}
这样做的好处是消除了if/else块,当你添加新的Place/Activity时,就少了一个需要修改的地方。不足之处在于,即使只是委托给Ginjector,它也会在某种程度上污染你的Place类,因为它包含了Activity创建行为。
public abstract class AbstractPlace extends Place {
public abstract Activity getActivity();
}
public class EditUserPlace extends AbstractPlace {
private Long id;
private User.Type type;
//getters and setters
@Override
public Activity getActivity() {
return App.getClientFactory().getEditUserPresenter().withPlace(this);
}
}
Defered binding 的 PlaceFactory 接口:
public interface PlaceFactory {
Place fromToken(String token);
String toToken(Place place);
}
以及用于注册位置类的注释
public @interface WithPlaces {
Class<? extends Place>[] value() default {};
}
以及PlaceFactoryGenerator
在你的GWT模块中设置生成器
<generate-with class="app.rebind.place.PlaceFactoryGenerator">
<when-type-assignable class="app.client.common.AppPlaceFactory"/>
</generate-with>
public class PlaceFactoryGenerator extends Generator {
private TreeLogger logger;
private TypeOracle typeOracle;
private JClassType interfaceType;
private String packageName;
private String implName;
private Class<? extends Place>[] placeTypes;
@Override
public String generate(TreeLogger logger,
GeneratorContext generatorContext, String interfaceName)
throws UnableToCompleteException {
this.logger = logger;
this.typeOracle = generatorContext.getTypeOracle();
this.interfaceType = typeOracle.findType(interfaceName);
this.packageName = interfaceType.getPackage().getName();
this.implName = interfaceType.getName().replace(".", "_") + "Impl";
// TODO Trocar annotation por scan
WithPlaces places = interfaceType.getAnnotation(WithPlaces.class);
assert (places != null);
Class<? extends Place>[] placeTypes = places.value();
this.placeTypes = placeTypes;
PrintWriter out = generatorContext.tryCreate(logger,
packageName, implName);
if (out != null) {
generateOnce(generatorContext, out);
}
return packageName + "." + implName;
}
private void generateOnce(GeneratorContext generatorContext, PrintWriter out) {
TreeLogger logger = this.logger.branch(
TreeLogger.DEBUG,
String.format("Generating implementation of %s",
interfaceType));
ClassSourceFileComposerFactory factory = new ClassSourceFileComposerFactory(
packageName, implName);
factory.addImport(interfaceType.getQualifiedSourceName());
factory.addImplementedInterface(interfaceType.getSimpleSourceName());
factory.addImport(StringBuilder.class.getCanonicalName());
factory.addImport(Map.class.getCanonicalName());
factory.addImport(HashMap.class.getCanonicalName());
factory.addImport(Place.class.getCanonicalName());
for (Class<? extends Place> place : placeTypes)
factory.addImport(place.getCanonicalName());
SourceWriter sw = factory.createSourceWriter(generatorContext, out);
sw.println("public Place fromToken(String token) {");
sw.indent();
sw.println("int barAt = token.indexOf('/');");
sw.println("String placeName = token;");
sw.println("Map<String, String> params = new HashMap<String, String>();");
sw.println("if (barAt > 0) {");
sw.indent();
sw.println("placeName = token.substring(0, barAt);");
sw.println("String[] keyValues = token.substring(barAt + 1).split(\"/\");");
sw.println("for (String item : keyValues) {");
sw.indent();
sw.println("int colonAt = item.indexOf(':');");
sw.println("if (colonAt > 0) {");
sw.indent();
sw.println("String key = item.substring(0, colonAt);");
sw.println("String value = item.substring(colonAt + 1);");
sw.println("params.put(key, value);");
sw.outdent();
sw.println("}");
sw.outdent();
sw.println("}");
sw.outdent();
sw.println("}\n");
for (Class<? extends Place> placeType : placeTypes) {
String placeTypeName = placeType.getSimpleName();
int replaceStrPos = placeTypeName.lastIndexOf("Place");
String placeName = placeTypeName.substring(0, replaceStrPos);
sw.println("if (placeName.equals(\"%s\")) {", placeName);
sw.indent();
sw.println("%s place = new %s();", placeTypeName, placeTypeName);
generateSetExpressions(sw, placeType);
sw.println("return place;");
sw.outdent();
sw.println("}\n");
}
sw.println("return null;");
sw.outdent();
sw.println("}\n");
sw.println("public String toToken(Place place) {");
sw.indent();
sw.println("StringBuilder token = new StringBuilder();\n");
for (Class<? extends Place> placeType : placeTypes) {
String placeTypeName = placeType.getSimpleName();
int replaceStrPos = placeTypeName.lastIndexOf("Place");
String placeName = placeTypeName.substring(0, replaceStrPos);
sw.println("if (place instanceof %s) {", placeTypeName);
sw.indent();
sw.println("%s newPlace = (%s)place;", placeTypeName, placeTypeName);
sw.println("token.append(\"%s\");", placeName);
generateTokenExpressions(sw, placeType);
sw.println("return token.toString();");
sw.outdent();
sw.println("}\n");
}
sw.println("return token.toString();");
sw.outdent();
sw.println("}\n");
sw.outdent();
sw.println("}");
generatorContext.commit(logger, out);
}
private void generateTokenExpressions(SourceWriter sw,
Class<? extends Place> placeType) {
for (Field field : placeType.getDeclaredFields()) {
char[] fieldName = field.getName().toCharArray();
fieldName[0] = Character.toUpperCase(fieldName[0]);
String getterName = "get" + new String(fieldName);
sw.println("token.append(\"/%s:\");", field.getName());
sw.println("token.append(newPlace.%s().toString());", getterName);
}
}
private void generateSetExpressions(SourceWriter sw, Class<? extends Place> placeType) {
for (Field field : placeType.getDeclaredFields()) {
char[] fieldName = field.getName().toCharArray();
fieldName[0] = Character.toUpperCase(fieldName[0]);
String setterName = "set" + new String(fieldName);
List<Method> methods = findMethods(placeType, setterName);
for (Method method : methods) {
Class<?>[] parameterTypes = method.getParameterTypes();
if (parameterTypes.length == 0 || parameterTypes.length > 1)
continue;
Class<?> parameterType = parameterTypes[0];
String exp = "%s";
if (parameterType == Character.class) {
exp = "%s.charAt(0)";
} else if (parameterType == Boolean.class) {
exp = "Boolean.parseBoolean(%s)";
} else if (parameterType == Byte.class) {
exp = "Byte.parseInt(%s)";
} else if (parameterType == Short.class) {
exp = "Short.parseShort(%s)";
} else if (parameterType == Integer.class) {
exp = "Integer.parseInt(%s)";
} else if (parameterType == Long.class) {
exp = "Long.parseLong(%s)";
} else if (parameterType == Float.class) {
exp = "Float.parseFloat(%s)";
} else if (parameterType == Double.class) {
exp = "Double.parseDouble(%s)";
} else if (parameterType.getSuperclass().isAssignableFrom(Enum.class)) {
exp = parameterType.getCanonicalName() + ".valueOf(%s)";
} else if (parameterType != String.class){
continue;
}
String innerExp = String.format("params.get(\"%s\")", field.getName());
String wrapperExp = String.format(exp, innerExp);
sw.println("place.%s(%s);", setterName, wrapperExp);
}
}
}
private List<Method> findMethods(Class<? extends Place> placeType, String name) {
Method[] methods = placeType.getMethods();
List<Method> found = new ArrayList<Method>();
for (Method method : methods) {
if (method.getName().equals(name)) {
found.add(method);
}
}
return found;
}
}
我的ActivityMapper长什么样子?
public class AppActivityMapper implements ActivityMapper {
public Activity getActivity(Place place) {
AbstractPlace abstractPlace = (AbstractPlace)place;
return abstractPlace.getActivity();
}
}
public class AppPlaceHistoryMapper implements PlaceHistoryMapper {
private AppPlaceFactory placeFactory = GWT.create(AppPlaceFactory.class);
public Place getPlace(String token) {
return placeFactory.fromToken(token);
}
public String getToken(Place place) {
return placeFactory.toToken(place);
}
}
@WithPlaces(value = {
HomePlace.class,
EditUserPlace.class
})
public interface AppPlaceFactory extends PlaceFactory {
}
实际上,我正在使用自定义的样板代码来完成这个任务:
public class PuksaActivityMapper implements ActivityMapper {
private HashMap<String, ActivityContainer> mappings;
@Inject
private SearchResultActivityContainer searchResultContainer;
@Inject
private HelloActivityContainer helloContainer;
@Override
public Activity getActivity(Place place) {
ActivityContainer container = getMappings().get(place.getClass().getName());
return container.getActivity(place);
}
public HashMap<String, ActivityContainer> getMappings() {
if (mappings == null) {
mappings = new HashMap<String, ActivityContainer>();
mappings.put(ShowResultsPlace.class.getName(), searchResultContainer);
mappings.put(HelloPlace.class.getName(), helloContainer);
}
return mappings;
}
}
其中ActivityContainer是一种简单的工厂类型(从这一点上可以使用经典的ioc方法)。
当然,现在只是用映射查找/填充替换了'if block',但结合Gin multibinding(目前不存在)可以完成它的工作。
另外,Gin enhancement - 通用GWT Activity/Places GinModule看起来很有前途。
首先,我在GWT问题上创建了一个问题,请给它点赞或评论。
public abstract class PlaceWithActivity extends Place {
public Activity getActivity();
}
然后在你的 ActivityMapper 中:
Public Activity get Activity(Place newPlace) {
return ((PlaceWithActivity) newPlace).getActivity();
}
你所有的地方都应该扩展PlaceWithActivity。唯一的问题是向下转换,这会导致ClassCastException。如果Place有getActivity(),那么你就不必向下转换,但它没有,所以你必须将其向下转换为一个具有此方法的类。
我不喜欢的是你必须进行强制类型转换并创建PlaceWithActivity类。如果GWT支持我正在做的事情,这将不是必需的。如果他们包括一个PlaceWithActivity类,你就不必创建它,如果ActivityManager只调用PlaceWithActivity类的getActivity()方法,那么你不仅不必向下转换,甚至不需要编写ActivityMapper!
我发现了一个很棒的方法,来自Igor Klimer。他使用访问者模式将决策逻辑推入Place实现中,这样ActivityMapper就保持简单。请查看他的博客文章以获取实现细节。