從android的數組列表中選擇一個隨機項 - 爲什麼我的代碼不工作？

Question

我正在嘗試創建一個小程序，該按鈕在按下按鈕時會從的Media對象中選擇一個隨機創意媒體。它不工作。我是Android的初學者，我不知道自己會出錯。任何人都可以在我的代碼中發現錯誤？

import java.util.ArrayList; 
import java.util.Random; 

import android.app.Activity; 
import android.content.DialogInterface; 
import android.content.DialogInterface.OnClickListener; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.widget.Button; 
import android.widget.TextView; 

public class MainActivity extends Activity { 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     setContentView(R.layout.activity_main); 

     Button button2; 
     TextView tvRandomMedia; 
     Random rnd = new Random(); 
     ArrayList<Media> media = new ArrayList<Media>(); 

     Media m1 = new Media("painting"); 
     Media m2 = new Media("Paper sculpturing"); 
     Media m3 = new Media("sawing"); 
     Media m4 = new Media("writing"); 
     Media m5 = new Media("dance"); 
     Media m6 = new Media("playing music"); 
     Media m7 = new Media("Graphic design"); 
     Media m8 = new Media("photography"); 

     button2=(Button) findViewById(R.id.button2); 
     button2.setOnClickListener((View.OnClickListener) button2Listener); 

     media.add(m1); 
     media.add(m2); 
     media.add(m3); 
     media.add(m4); 
     media.add(m5); 
     media.add(m6); 
     media.add(m7); 
     media.add(m8); 

     tvRandomMedia = (TextView) findViewById(R.id.textView1); 
    }  

    OnClickListener button2Listener=new OnClickListener() { 

     @Override 
     public void onClick(View v) { 
     // TODO Auto-generated method stub 
      doRandomMedia();  
     } 

     public void doRandomMedia() { 
      int creativity = rnd.nextInt(media.size()); 
      Media expression = media.get(creativity); 
      System.out.print("The media of this week is "+ expression); 
     } 
    } 
} 

Answer 1

我想你已經把doRandomMedia（）方法放在onClickListener中。嘗試下面的代碼，看看它是否有幫助。

import java.util.ArrayList; 
import java.util.Random; 
import android.app.Activity; 
import android.os.Bundle; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 
import android.widget.TextView; 

public class MainActivity45 extends Activity { 

    Button button2; 
    TextView tvRandomMedia; 
    Random rnd = new Random(); 
    ArrayList<Media> media = new ArrayList<Media>(); 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    setContentView(R.layout.activity_main); 

    Media m1 = new Media("painting"); 
    Media m2 = new Media("Paper sculpturing"); 
    Media m3 = new Media("sawing"); 
    Media m4 = new Media("writing"); 
    Media m5 = new Media("dance"); 
    Media m6 = new Media("playing music"); 
    Media m7 = new Media("Graphic design"); 
    Media m8 = new Media("photography"); 

    button2 = (Button) findViewById(R.id.button2); 
    button2.setOnClickListener((View.OnClickListener) button2Listener); 

    media.add(m1); 
    media.add(m2); 
    media.add(m3); 
    media.add(m4); 
    media.add(m5); 
    media.add(m6); 
    media.add(m7); 
    media.add(m8); 

    tvRandomMedia = (TextView) findViewById(R.id.textView1); 
} 

OnClickListener button2Listener = new OnClickListener() { 

    @Override 
    public void onClick(View v) { 
     // TODO Auto-generated method stub 
     doRandomMedia(); 
    } 

}; 

public void doRandomMedia() { 
    int creativity = rnd.nextInt(media.size()); 
    Media expression = media.get(creativity); 
    System.out.print("The media of this week is " + expression); 
} 
} 

Answer 2

首先將您的OnClickListener的類型更改爲View.OnClickListener。

其次，media無法從您的OnClickListener到達。

也許你可以做這樣的事情：

... 
button2.setOnClickListener(new View.OnClickListener() { 
    @Override 
    public void onClick(View v) { 
     // TODO Auto-generated method stub 
     doRandomMedia(); 
    } 

    public void doRandomMedia() { 
     int creativity = rnd.nextInt(media.size()); 
     Media expression = media.get(creativity); 
     System.out.print("The media of this week is "+ expression); 
    } 
}); 
... 

Answer 3

在doRandomMedia（）方法，你試圖從「媒體」列表，在方法的onCreate（）中定義的信息。你應該移動ArrayList media = new ArrayList（）;從方法到類

public class MainActivity extends Activity { 
    ArrayList<Media> media = new ArrayList<Media>(); 

    @Override 
    protected void onCreate(Bundle savedInstanceState) {} 
}