Question

我有以下特点：

package com.czhou.dailyprincetoniannewspaper;

import android.os.Bundle;
import android.support.design.widget.CoordinatorLayout;
import android.support.design.widget.TabLayout;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.widget.ProgressBar;
import android.widget.RelativeLayout;

import java.util.ArrayList;
import java.util.List;
/**
 * Created by czhou on 11/21/2015.
 */
public class MainActivity extends AppCompatActivity {

    private Toolbar toolbar;
    private TabLayout tabLayout;
    private ViewPager viewPager;
    private ProgressBar mProgressBar;
    private CoordinatorLayout coordinatorLayout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);


        viewPager = (ViewPager) findViewById(R.id.viewpager);
        setupViewPager(viewPager);

        tabLayout = (TabLayout) findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(viewPager);
    }

    private void setupViewPager(ViewPager viewPager){
        ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
        adapter.addFragment(new PUNewsFragment(), "News");
        adapter.addFragment(new PUSportsFragment(), "Sports");

        viewPager.setAdapter(adapter);
    }

    class ViewPagerAdapter extends FragmentPagerAdapter {
        private final List<Fragment> mFragmentList = new ArrayList<>();
        private final List<String> mFragmentTitleList = new ArrayList<>();

        public ViewPagerAdapter(FragmentManager manager) {
            super(manager);
        }

        @Override
        public Fragment getItem(int position) {
            return mFragmentList.get(position);
        }

        @Override
        public int getCount() {
            return mFragmentList.size();
        }

        public void addFragment(Fragment fragment, String title) {
            mFragmentList.add(fragment);
            mFragmentTitleList.add(title);
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return mFragmentTitleList.get(position);
        }
    }
}

我想创建另一个特性，它在一个函数中采用一个实现pub trait Stream<T: Read + Write + AsRawFd>: Sized { fn new(stream: T) -> Result<Self, Error>; fn recv(&mut self) -> Result<Vec<u8>, Error>; fn send(&mut self, buf: &[u8]) -> Result<usize, Error>; }作为参数的类型，如下所示：

Stream

我已经尝试了几种变体来定位特征定义，但我似乎总是得到错误：

pub trait EventHandler<T: Stream> {
    fn on_data_received(&mut self, stream: T, buffer: Vec<u8>);
    fn on_stream_closed(&mut self, id: u32);
}

这个的正确语法是什么？

Answer 1

您需要在<T: Stream>界限上指定一个类型参数，如下所示：

pub trait EventHandler<T: Stream<U>, U: Read + Write + AsRawFd> {
    fn on_data_received(&mut self, stream: T, buffer: Vec<u8>);
    fn on_stream_closed(&mut self, id: u32);
}

您还可以使用where子句编写边界：

pub trait EventHandler<T, U> where
    T: Stream<U>,
    U: Read + Write + AsRawFd
{
    fn on_data_received(&mut self, stream: T, buffer: Vec<u8>);
    fn on_stream_closed(&mut self, id: u32);
}

另一种选择是使用相关类型。像这样定义Stream：

pub trait Stream: Sized {
    type T: Read + Write + AsRawFd;

    fn new(stream: Self::T) -> Result<Self, Error>;
    fn recv(&mut self) -> Result<Vec<u8>, Error>;
    fn send(&mut self, buf: &[u8]) -> Result<usize, Error>;
}

然后您EventHandler的原始定义将起作用。

具有泛型的特征的语法

1 个答案: