希望線程中出現簡單錯誤Android

Question

我對Android有點新。使用一個讓用戶輸入數字然後計算斐波納契數列的應用程序，然後以1秒的間隔顯示序列中的每個元素。但是當我嘗試在for循環中使用線程顯示時，我遇到了一個問題。我嘗試從數組列表中打印，但它給我一個錯誤，我的計數器變量（j）。我試着在一個更簡單的應用程序中運行這個相同的確切方法，數組列表工作得很好。我不知道爲什麼這次不行。我希望這是一個簡單明顯的錯誤。誰能告訴我爲什麼？代碼下面貼：

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

一個簡單的解決方法來解決你的問題是用這種方式來聲明一個臨時變量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

你有一個更嚴重的問題。 你正試圖從一個線程操縱一個texView。這是不允許的。只有GUI線程可以操縱屏幕對象或發生不良事情。

看看AsyncTask。它旨在解決您正在嘗試解決的問題。

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