希望线程中出现简单错误Android

Question

我对Android有点新。使用一个让用户输入数字然后计算斐波纳契数列的应用程序，然后以1秒的间隔显示序列中的每个元素。但是当我尝试在for循环中使用线程显示时，我遇到了一个问题。我尝试从数组列表中打印，但它给我一个错误，我的计数器变量（j）。我试着在一个更简单的应用程序中运行这个相同的确切方法，数组列表工作得很好。我不知道为什么这次不行。我希望这是一个简单明显的错误。谁能告诉我为什么？代码下面贴：

public class MainActivity extends Activity { 

// primary widgets 
private EditText editText; 
private TextView textView; 
private Button button1; 
Thread thread; 
static ArrayList<Integer> fibList = new ArrayList<Integer>(); 

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

    editText = (EditText) findViewById(R.id.editText1); 
    textView = (TextView) findViewById(R.id.textView2); 
    button1 = (Button) findViewById(R.id.button1); 

    //Attempt to clear TextView 
    textView.setText(""); 

    button1.setOnClickListener(new OnClickListener() { 

     @Override 
     public void onClick(View v) { 

      //Clear Textview 
      String array = " "; 
      fibList.clear(); 
      textView.setText(array); 

      final String input = editText.getText().toString(); 
      int number = Integer.parseInt(input); 
      int tmp = 0; 

      // confirm input 
      if (number < 20) { 
       Toast.makeText(getApplicationContext(), 
         "You entered: " + number, Toast.LENGTH_LONG).show(); 
       for (int i = 0; i <= number; i++) { 
        fibList.add(fib(i)); 

        // sum even numbers 
        if (fib(i) % 2 == 0) { 
         tmp += fib(i); 

        } 

       } 
      } else { 
       Toast.makeText(getApplicationContext(), 
         "Number is too Large: " + number, Toast.LENGTH_LONG) 
         .show(); 
      } 

      Log.i("TEST", "ARRAY"+fibList); 

      thread = new Thread(new Runnable(){ 

        @Override 
        public void run(){ 

        for(int j = 0; j < fibList.size(); j++){ 
         runOnUiThread(new Runnable(){ 

         @Override 
         public void run(){ 

          //ERROR OCCURS HERE: Cannot refer to a non-final variable j 
          //inside an inner class defined in a different method 
          textView.append(fibList.get(j).toString()); 

          textView.append(""); 
         } 
         }); 
         try { 
         Thread.sleep(1000); 
        } catch (InterruptedException e) { 
         // TODO Auto-generated catch block 
         e.printStackTrace(); 
        } //wait one second 
        } 
        } 

       }); 
       thread.start(); 
     } 

    }); 
} 

// run fibonacci sequence 
public static int fib(int n) { 
    if (n < 2) { 
     return n; 
    } else { 
     return fib(n - 1) + fib(n - 2); 
    } 
} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.main, menu); 
    return true; 
} 

}

Answer 1

一个简单的解决方法来解决你的问题是用这种方式来声明一个临时变量final：

 for(int j = 0; j < fibList.size(); j++){ 
      final int finalJ = j; 
      runOnUiThread(new Runnable(){ 

       @Override 
       public void run(){ 
        //ERROR OCCURS HERE: Cannot refer to a non-final variable j 
        //inside an inner class defined in a different method 
        textView.append(fibList.get(finalJ).toString()); 
        textView.append(""); 
       } 
      }); 

Answer 2

你有一个更严重的问题。 你正试图从一个线程操纵一个texView。这是不允许的。只有GUI线程可以操纵屏幕对象或发生不良事情。

看看AsyncTask。它旨在解决您正在尝试解决的问题。

http://developer.android.com/reference/android/os/AsyncTask.html