java - 在 Android 中使用线程时出现错误

Question

I create a simple Project to load all images in drawable

这是我的代码

public void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    list = (ImageView)findViewById(R.id.tung);
    ct = getApplicationContext();
    try
    {
        IDs = getAllResourceIDs(R.drawable.class);
        n= IDs.length;
        dem=0;
        list.setOnClickListener(new View.OnClickListener()
         {
            public void onClick(View v)
            {
                ++dem;
                list.setImageResource(IDs[dem]);
                if(dem==n-1)
                    dem=0;
            }
        });

        Thread x = new Thread(
                new Runnable ()
                {
                    public void run()
                    {
                        while(true)
                        {
                            try
                            {
                                ++dem;
                                //Toast.makeText(ct, ""+dem, 20).show();
                                list.setImageResource(IDs[dem]);
                                if(dem==n-1)
                                    dem=0;
                            }
                            catch(Exception e)
                            {
                                //Toast.makeText(ct,e.toString(), 200).show();
                            }
                        }
                    }
                }
                );
        x.start();
    }
    catch(Exception e)
    {
        Toast.makeText(this,e.toString(), 200).show();
    }
}

anh 这里是 getAllResourceIDs 函数来获取所有 id

private int[] getAllResourceIDs(Class<?> aClass) throws IllegalArgumentException{
    /* Get all Fields from the class passed. */
    Field[] IDFields = aClass.getFields();

    /* int-Array capable of storing all ids. */
    int[] IDs = new int[IDFields.length];

    try {
            /* Loop through all Fields and store id to array. */
            for(int i = 0; i < IDFields.length; i++){
                    /* All fields within the subclasses of R
                     * are Integers, so we need no type-check here. */

                    // pass 'null' because class is static
                    IDs[i] = IDFields[i].getInt(null);
            }
    } catch (Exception e) {
            /* Exception will only occur on bad class submitted. */
            throw new IllegalArgumentException();
    }
    return IDs;

文件 main.xml 只有一个 id = "tung"的 ImageView我尝试使用名为 x 的 Thead 加载所有图像通过使用代码list.setImageResource(IDs[dem]);正如你在我的代码中看到的但什么也没发生你能给我解释一下吗!非常感谢!

Answer 1

对于初学者来说，catch (Exception e) 几乎从来都不是一个好主意，因为它隐藏了发生错误时可以获得的所有有意义的信息。

您的错误特别出现在后台线程中的这一行:

list.setImageResource(IDs[dem]);

后台线程不允许操作 UI 对象。相反，您需要使用 AsyncTask (更简单)或 Handler (高级)