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我是 Android 开发的初学者，我正在使用我的第一个应用程序，但遇到了一个问题。我必须下载一些图片扔到互联网上，并在活动中展示它们。在下载图像之前，我有一个 UI 延迟，所以我必须使用多线程。

我阅读了更多关于它的信息，我认为最简单的是 AsyncTask，但我收到了一个例外：Only the original thread that created a view hierarchy can touch its views.

我需要帮助。任何人都可以帮助我吗？代码是这样的：

public class Main extends Activity{



protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    Download download = new Download();
    download.execute(null);
}

private class Download extends AsyncTask<String, Void, String>{
    ImageButtonOverloaded[] imgView = new ImageButtonOverloaded[24];
    TextView[] textView = new TextView[24];
    @Override
    protected String doInBackground(String... params) {
        try{

            URL url = null;
            url = new URL(StaticClass.URL_HOST + "front_page_last_games_plaintext.php");
            URLConnection conn = url.openConnection();
            BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String line;

            initCovers();
            int i = 0;
            Log.d("SYNC", "i = 0");
            while((line = reader.readLine()) != null){
                String gameInfo[] = line.split("<NEXT>");
                //Log.d("SYNC", gameInfo[0]);
                //Log.d("SYNC", gameInfo[1]);
                Drawable x = ImageOperations(Main.this, StaticClass.URL_HOST + "resize.php?imagine=" + gameInfo[0] ,"image.jpg");

                Log.d("SYNC", "in while");
                imgView[i].setImageDrawable(x);
                Log.d("SYNC", "in while");
                imgView[i].setGameID(gameInfo[0]);
                imgView[i].setOnClickListener(new OnClickListener() {

                    public void onClick(View v) {
                        ImageButtonOverloaded temp = (ImageButtonOverloaded) v;
                        Intent intent = new Intent(Main.this, Single.class);
                        intent.putExtra("ID", temp.getGameID());
                        startActivity(intent);

                    }
                });

                textView[i].setText(gameInfo[1]);
                textView[i].setGravity(Gravity.TOP);
                textView[i].setGravity(Gravity.CENTER_HORIZONTAL);
                textView[i].setTextColor(Color.WHITE);
                i++;
            }
        }catch(Exception ex){
            Log.d("SYNC", ex.getMessage());
        }
        return null;
    }
    private Drawable ImageOperations(Context ctx, String url, String saveFilename) {
        try {
            InputStream is = (InputStream) this.fetch(url);
            Drawable d = Drawable.createFromStream(is, "src");
            return d;
        } catch (MalformedURLException e) {
            e.printStackTrace();
            return null;
        } catch (IOException e) {
            e.printStackTrace();
            return null;
        }
    }

    public Object fetch(String address) throws MalformedURLException,IOException {
        URL url = new URL(address);
        Object content = url.getContent();
        return content;
    }
    private void initCovers(){
        imgView[0] = (ImageButtonOverloaded) findViewById(R.id.imageButton1);
        imgView[1] = (ImageButtonOverloaded) findViewById(R.id.imageButton2);
        imgView[2] = (ImageButtonOverloaded) findViewById(R.id.imageButton3);
        imgView[3] = (ImageButtonOverloaded) findViewById(R.id.imageButton4);
        imgView[4] = (ImageButtonOverloaded) findViewById(R.id.imageButton5);
        imgView[5] = (ImageButtonOverloaded) findViewById(R.id.imageButton6);
        imgView[6] = (ImageButtonOverloaded) findViewById(R.id.imageButton7);
        imgView[7] = (ImageButtonOverloaded) findViewById(R.id.imageButton8);
        imgView[8] = (ImageButtonOverloaded) findViewById(R.id.imageButton9);
        imgView[9] = (ImageButtonOverloaded) findViewById(R.id.imageButton10);
        imgView[10] = (ImageButtonOverloaded) findViewById(R.id.imageButton11);
        imgView[11] = (ImageButtonOverloaded) findViewById(R.id.imageButton12);
        imgView[12] = (ImageButtonOverloaded) findViewById(R.id.imageButton13);
        imgView[13] = (ImageButtonOverloaded) findViewById(R.id.imageButton14);
        imgView[14] = (ImageButtonOverloaded) findViewById(R.id.imageButton15);
        imgView[15] = (ImageButtonOverloaded) findViewById(R.id.imageButton16);
        imgView[16] = (ImageButtonOverloaded) findViewById(R.id.imageButton17);
        imgView[17] = (ImageButtonOverloaded) findViewById(R.id.imageButton18);
        imgView[18] = (ImageButtonOverloaded) findViewById(R.id.imageButton19);
        imgView[19] = (ImageButtonOverloaded) findViewById(R.id.imageButton20);
        imgView[20] = (ImageButtonOverloaded) findViewById(R.id.imageButton21);
        imgView[21] = (ImageButtonOverloaded) findViewById(R.id.imageButton22);
        imgView[22] = (ImageButtonOverloaded) findViewById(R.id.imageButton23);
        imgView[23] = (ImageButtonOverloaded) findViewById(R.id.imageButton24);

        textView[0] = (TextView) findViewById(R.id.textView1);
        textView[1] = (TextView) findViewById(R.id.textView2);
        textView[2] = (TextView) findViewById(R.id.textView3);
        textView[3] = (TextView) findViewById(R.id.textView4);
        textView[4] = (TextView) findViewById(R.id.textView5);
        textView[5] = (TextView) findViewById(R.id.textView6);
        textView[6] = (TextView) findViewById(R.id.textView7);
        textView[7] = (TextView) findViewById(R.id.textView8);
        textView[8] = (TextView) findViewById(R.id.textView9);
        textView[9] = (TextView) findViewById(R.id.textView10);
        textView[10] = (TextView) findViewById(R.id.textView11);
        textView[11] = (TextView) findViewById(R.id.textView12);
        textView[12] = (TextView) findViewById(R.id.textView13);
        textView[13] = (TextView) findViewById(R.id.textView14);
        textView[14] = (TextView) findViewById(R.id.textView15);
        textView[15] = (TextView) findViewById(R.id.textView16);
        textView[16] = (TextView) findViewById(R.id.textView17);
        textView[17] = (TextView) findViewById(R.id.textView18);
        textView[18] = (TextView) findViewById(R.id.textView19);
        textView[19] = (TextView) findViewById(R.id.textView20);
        textView[20] = (TextView) findViewById(R.id.textView21);
        textView[21] = (TextView) findViewById(R.id.textView22);
        textView[22] = (TextView) findViewById(R.id.textView23);
        textView[23] = (TextView) findViewById(R.id.textView24);

    }
}}
4

1 回答 1

5

doInBackgorund()是一个非 UI 线程，您无法访问其中的 UI 元素。doInBackground() 中的代码在一个单独的非 UI 线程上运行，该线程无法访问布局中定义的 UI 元素。此外，由于您通过意图调用另一个 Activity，因此您应该始终牢记 Activity 在 UI 线程上运行，因此您永远不应该从非 UI 线程内启动另一个 Activity。

因此，从 doInBackground() 内部删除访问 UI 元素的代码，然后将其放入内部onPostExecute()，这是一个 UI 线程，在 doInBackground() 完成后台处理后调用。

int i =0; // global variable
Drawable drawableArray []; // global array to store all the drawables 

doInBackground(String... params) {
        try{

            URL url = null;
            url = new URL(StaticClass.URL_HOST + "front_page_last_games_plaintext.php");
            URLConnection conn = url.openConnection();
            BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String line;

            initCovers();
            while((line = reader.readLine()) != null){
                String gameInfo[] = line.split("<NEXT>");
                //Log.d("SYNC", gameInfo[0]);
                //Log.d("SYNC", gameInfo[1]);
                drawableArray[i] = ImageOperations(Main.this, StaticClass.URL_HOST + "resize.php?imagine=" + gameInfo[0] ,"image.jpg");
                i++;
}

onPostExecute()
{
   for(j=0;j<=i;j++)

                Log.d("SYNC", "in while");
                imgView[j].setImageDrawable(drawableArray[j]);
                Log.d("SYNC", "in while");
                imgView[j].setGameID(gameInfo[0]);
                imgView[j].setOnClickListener(new OnClickListener() {

                    public void onClick(View v) {
                        ImageButtonOverloaded temp = (ImageButtonOverloaded) v;
                        Intent intent = new Intent(Main.this, Single.class);
                        intent.putExtra("ID", temp.getGameID());
                        startActivity(intent);

                    }
                });

                textView[j].setText(gameInfo[1]);
                textView[j].setGravity(Gravity.TOP);
                textView[j].setGravity(Gravity.CENTER_HORIZONTAL);
                textView[j].setTextColor(Color.WHITE);
                j++;
            }
}

编辑：正如@Luksprog和@tolgap所指出的，主ui 线程上的图像处理部分操作很长，可能会使UI 无响应。因此，最好也在后台线程上进行图像处理，然后使用 onPostExecute() 来设置图像位图并更新其他 UI 元素。通过在后台进行处理，使用全局数组来存储 Drawable，然后在 onPostExecute() 中更新 UI。

于 2012-10-06T19:17:34.253 回答