私有OnClickListener clickFunction =新OnClickListener(){stmt；}

Question

我在android上尝试了一个示例应用程序。我可以得到输出。

studentFormsActiviyt.java

package com.example.android.accelerometerplay;

import android.app.Activity;
import android.view.View;
import android.view.View.OnClickListener;
import android.os.Bundle;
import android.widget.Button;
import android.widget.Toast;
import android.content.Context;

public class StudentFormsActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        // To specify the actions of the Buttons
        Button accept = (Button) findViewById(R.id.myButton1);
        Button reject = (Button) findViewById(R.id.myButton2);

        accept.setOnClickListener(clickFunction);
        reject.setOnClickListener(clickFunction);
    }

    private OnClickListener clickFunction = new OnClickListener(){
        public void onClick(View v){
            Context context = getApplicationContext();
            CharSequence text;

            switch(v.getId()){
               case R.id.myButton1: text="accept was pushed"; 
                                    break;
               case R.id.myButton2: text="reject was pushed"; 
                                    break;
               default: text="We didn't know what was pressed :(";  
            }

            int duration = Toast.LENGTH_SHORT;
            Toast toast = Toast.makeText(context,text,duration);
            toast.show();

        }
    }
 }

main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView 
    android:id="@+id/myLabel"
    android:text="Name of the student:" 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    />
<EditText
    android:id="@+id/myText"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content"
    android:layout_below="@id/myLabel" 
    />
<Button
    android:id="@+id/myButton1"
    android:text="Accept:" 
    android:textColor="#00FF00"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content"
    android:layout_below="@id/myText"
    android:layout_alignParentRight="true"
    />
<Button
    android:id="@+id/myButton2"
    android:text="Reject:" 
    android:textColor="#FF0000"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content"
    android:layout_toLeftOf="@id/myButton1"
    android:layout_alignTop="@id/myButton1"
    />
</RelativeLayout>

但是我不能理解“私有OnClickListener clickFunction =新OnClickListener(){stmt；}”这个类的定义。我们曾经将类声明为私有类classname{stmt}；，然后用来创建类的实例。但在上面的第一个声明中，他们创建了类的实例，然后定义。他们为什么要这样做。请帮我理解一下。

Answer 1

OnClickListener是一个接口。当在该接口上使用new操作符时，实际上是为该接口提供了一个实现(一个匿名内部类)。类实现是匿名的，因为您没有在编译时为其提供名称，而将在运行时为其分配名称。您还可以为它提供一个显式的实现，作为实现OnClickListener接口的私有内部类。

    package com.example.android.accelerometerplay;

    import android.app.Activity;
    import android.view.View;
    import android.view.View.OnClickListener;
    import android.os.Bundle;
    import android.widget.Button;
    import android.widget.Toast;
    import android.content.Context;

    public class StudentFormsActivity extends Activity {
    /** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    // To specify the actions of the Buttons
    Button accept = (Button) findViewById(R.id.myButton1);
    Button reject = (Button) findViewById(R.id.myButton2);

    accept.setOnClickListener(clickFunction);
    reject.setOnClickListener(clickFunction);
}

private OnClickListener clickFunction = new OnClickClass();

private class OnClickClass implements OnClickListener{
    public void onClick(View v){
        Context context = getApplicationContext();
        CharSequence text;

        switch(v.getId()){
           case R.id.myButton1: text="accept was pushed"; 
                                break;
           case R.id.myButton2: text="reject was pushed"; 
                                break;
           default: text="We didn't know what was pressed :(";  
        }

        int duration = Toast.LENGTH_SHORT;
        Toast toast = Toast.makeText(context,text,duration);
        toast.show();

    }
 }
}

Answer 2

private OnClickListener clickFunction = new OnClickListener(){stmt; }

但这不是私有类的定义..它是私有成员类的定义.

它就像这样：

//declaring member class
private OnClickListener clickFunction;

private OnClickListener clickFunctionMake(){
    return new OnClickListener(){stmt; };
}

 @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
//.....initializing member class
        clickFunction=clickFunctionMake();
///....
}

Answer 3

private OnClickListener clickFunction = new OnClickListener(){stmt; }

在上面的语句中，OnClickListener不是它的类，而是android.view.View类中的接口。我们不能通过使用关键字来实例化任何接口。

在您在这里发布的代码中，他通过实现View.OnClickListener接口来创建实例clickFunction，因此他还实现了onClick方法。

他为两个按钮使用了单实例clickFunction，以消除两个侦听器。

我希望你能理解这一点，这可能会对你有所帮助。