Question

我正在研究与“可选协议要求”相关的 The Swift Programming Language 一书中的一个示例。我在以下代码中遇到问题。

import Foundation

@objc protocol CounterDataSource {
    optional func incrementForCount(count: Int) -> Int
    optional var fixedIncrement: Int { get }
}

@objc class Counter {
    var count = 0
    var dataSource: CounterDataSource?
    func increment() {
        if let amount = dataSource?.incrementForCount?(count) {
            count += amount
        } else if let amount = dataSource?.fixedIncrement {
            count += amount
        }
    }
}

class ThreeSource: CounterDataSource {
    var fixedIncrement = 3
}

var counter = Counter()
counter.dataSource = ThreeSource()

for _ in 1...4 {
    counter.increment()
    println(counter.count)
}

不应该这样吗？当println()应该递增3秒时，import android.os.Bundle; import android.support.v7.app.ActionBarActivity; import android.view.Menu; import android.view.MenuItem; import android.view.View; import android.widget.Toast; public class MyActivity extends ActionBarActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_my); } public void buttonHandler(View view) { Toast.makeText(getApplicationContext(), "Thank you for using Hinglish", Toast.LENGTH_LONG).show(); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.menu_my, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { // Handle action bar item clicks here. The action bar will // automatically handle clicks on the Home/Up button, so long // as you specify a parent activity in AndroidManifest.xml. int id = item.getItemId(); //noinspection SimplifiableIfStatement if (id == R.id.action_settings) { return true; } return super.onOptionsItemSelected(item); } }连续输出0。

Answer 1

@objc protocol需要@objc实施。

在你的情况下：

class ThreeSource: CounterDataSource {
    @objc var fixedIncrement = 3
//  ^^^^^ YOU NEED THIS!
}

没有它，Objective-C运行时找不到属性。

可选的协议要求，我无法使其工作

1 个答案: