Question

我对Android有点新鲜。处理一个应用程序，让用户输入一个数字，然后计算斐波纳契数列，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循环中使用线程进行显示时，我遇到了问题。我尝试从数组列表打印但它给我一个错误与我的计数器变量（j）。我尝试在一个更简单的应用程序中运行这个相同的方法，并且数组列表工作得很好。我不知道为什么这次不起作用。我希望这是一个简单明显的错误。谁能告诉我为什么？代码发布如下：

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

解决问题的简单解决方法是以这种方式声明临时final变量：

       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。您正在尝试从线程中操作texView。这是不允许的。只有GUI线程可以操作屏幕对象或者Bad Things Happen。

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

希望线程Android中的简单错误

2 个答案: