[英]Dependency Injection: How to get access to the corresponding ProductView that executes the Command?
我想为每个产品视图执行命令。 考虑 10 个产品视图,每个视图都可以执行PrintProductViewCommand
。 此命令接收构造函数ProductView
并打印其名称。 由于它@Inject
,每次创建命令时容器都会创建一个新的ProductView。 以下示例显示了我想要做什么:
public class InjectionTest {
public static void main(String[] args) {
Injector injector = Guice.createInjector(new AbstractModule() {
@Override
protected void configure() {
bind(ProductView.class);
bind(CommandExecutor.class);
bind(PrintProductViewNameCommand.class);
install(new FactoryModuleBuilder().implement(ProductView.class, ProductView.class)
.build(ProductViewFactory.class));
}
});
List<ProductView> productViews = new ArrayList<>();
ProductViewFactory factory = injector.getInstance(ProductViewFactory.class);
for (int i = 0; i < 10; i++) {
productViews.add(factory.create("Name: " + String.valueOf(i)));
}
System.out.println("Done creating");
//Now sometime in future, each product view calls print method
productViews.forEach(ProductView::print);
}
private static interface ProductViewFactory {
ProductView create(String name);
}
private static class ProductView {
private String name; //simulate a property
private CommandExecutor executor;
public ProductView() {
//Guice throws exception when this is missing
//Probably because it is being asked in PrintProductViewCommand
}
@AssistedInject
public ProductView(@Assisted String name, CommandExecutor executor) {
this.name = name;
this.executor = executor;
}
public String getName() {
return name;
}
//assume some time product view it self calls this method
public void print() {
executor.execute(PrintProductViewNameCommand.class);
}
}
@Singleton
private static class CommandExecutor {
@Inject
private Injector injector;
public void execute(Class<? extends Command> cmdType) {
injector.getInstance(cmdType).execute();
}
}
private static class PrintProductViewNameCommand implements Command {
private ProductView view;
@Inject
public PrintProductViewNameCommand(ProductView view) {
this.view = view;
}
@Override
public void execute() {
//Want to print "Name: something" here
System.out.println(view.getName());
}
}
private static interface Command {
void execute();
}
}
如果我向 Command 接口添加一个参数并使其成为Command<T>
,这个问题就解决了。 然后CommandExecutor
将有这个方法:
public <T> void execute(Class<? extends Command<T>> cmdType, T parameter) {
injector.getInstance(cmdType).execute(parameter);
}
所以,我的PrintProductViewNameCommand
现在是class PrintProductViewNameCommand implements Command<ProductView>
,在产品视图中:
public void print() {
executor.execute(PrintProductViewNameCommand.class,this);
}
但是,命令模式在execute()
中没有参数。 我还在某处看到添加参数是一种反模式。
当然,命令很简单。 假设该命令也有其他依赖项,如服务等。
有什么办法可以实现吗? 也许我做错了什么,可能是整个 DI 情况。
当不使用依赖注入时,我会做这样的事情:
ProductView view = new ProductView();
Command command = new PrintProductViewNameCommand(view);
view.setPrintCommand(command);
但是如何使用 DI 呢?
所以这是有效的,虽然我不确定它是否是你想要做的 100%。
public class InjectionTest {
public static void main(String[] args) {
Injector injector = Guice.createInjector(new AbstractModule() {
@Override
protected void configure() {
bind(CommandExecutor.class);
bind(ProductView.class);
install(new FactoryModuleBuilder()
.implement(ProductView.class, ProductView.class)
.build(ProductViewFactory.class));
install(new FactoryModuleBuilder()
.implement(PrintProductViewNameCommand.class, PrintProductViewNameCommand.class)
.build(PrintProductViewNameCommand.Factory.class));
}
});
ProductViewFactory factory = injector.getInstance(ProductViewFactory.class);
List<ProductView> productViews = new ArrayList<>();
for (int i = 0; i < 10; i++) {
productViews.add(factory.create("Name: " + i));
}
System.out.println("Done creating");
//Now sometime in future, each product view calls print method
productViews.forEach(ProductView::print);
}
private interface ProductViewFactory {
ProductView create(String name);
}
private static class ProductView {
private String name;
private CommandExecutor executor;
private PrintProductViewNameCommand printProductViewNameCommand;
@AssistedInject
public ProductView(@Assisted String name, PrintProductViewNameCommand.Factory printProductViewNameCommandFactory, CommandExecutor executor) {
this.name = name;
this.executor = executor;
this.printProductViewNameCommand = printProductViewNameCommandFactory.create(this);
}
public ProductView() {}
public String getName() {
return name;
}
//assume some time product view it self calls this method
public void print() {
executor.execute(printProductViewNameCommand);
}
}
@Singleton
private static class CommandExecutor {
public void execute(Command command) {
command.execute();
}
}
private static class PrintProductViewNameCommand implements Command {
private final ProductView view;
@AssistedInject
public PrintProductViewNameCommand(@Assisted ProductView view) {
this.view = view;
}
static interface Factory {
PrintProductViewNameCommand create(ProductView productView);
}
@Override
public void execute() {
//Want to print "Name: something" here
System.out.println(view.getName());
}
}
private static interface Command {
void execute();
}
}
基本上你遇到的是一个循环依赖问题( https://github.com/google/guice/wiki/CyclicDependencies#use-factory-methods-to-tie-two-objects-together )也被激怒了事实上,您在ProductView
中有一个额外的AssistedInject
。
顺便说一下,我在此示例中使用的是 Guice 3。
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