Question

我正在尝试使用ArrayList填充listview，而ArrayList必须根据此处https://stackoverflow.com/a/22326209/8520030的内容从Asynctask返回。我试图将zip文件显示为listview。我使用asynctask通常需要花费太多时间在listview中加载项目。 但是使用Asynctask时listview中没有显示任何内容。就像它没有填充listview项目。我这样做到现在为止。

public interface IAsyncTask {

    ArrayList<String> IAmFinished(ArrayList<File> arrayList);
}

public class MainActivity2 extends AppCompatActivity implements IAsyncTask {

public static ArrayList<File> fileList = new ArrayList<>();
public static ArrayList<String> name = new ArrayList<>();
Longoperation longoperation;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main2);

    File dir1 = new File(Environment.getExternalStorageDirectory().getPath());
    longoperation = new Longoperation(dir1, this);
    longoperation.execute();
    JazzyListView lv = (JazzyListView) findViewById(R.id.list);


    lv.setAdapter(new ArrayAdapter<>(this,
            android.R.layout.simple_list_item_1, name));
}

@Override
public ArrayList<String> IAmFinished(ArrayList<File> list) {
    for(int i=0;i< list.size();i++){
        name.add(list.get(i).getName());
    }
    return name;
}

private class Long operation extends AsyncTask<File, Void, ArrayList<File>>{

    File dir;
    private static final String TAG = "com.example.dell_1.myapp3.Zip";
    private IAsyncTask asyncTaskListener;

    public Longoperation(File dir,IAsyncTask asyncTaskListener) {
        this.dir = dir;
        this.asyncTaskListener = asyncTaskListener;
    }

    @Override
    protected ArrayList<File> doInBackground(File... params) {
        File listFile[] = dir.listFiles();
        if (listFile != null && listFile.length > 0) {
            for (int i = 0; i < listFile.length; i++) {

                if (listFile[i].isDirectory()) {
                    doInBackground(listFile[i]);

                } else {

                    boolean booleanpdf = false;
                    if (listFile[i].getName().endsWith(".zip") || listFile[i].getName().endsWith(".jar")) {

                        for (int j = 0; j < fileList.size(); j++) {
                            if (fileList.get(j).getName().equals(listFile[i].getName())) {
                                booleanpdf = true;
                            } else {

                            }
                        }

                        if (booleanpdf) {
                            booleanpdf = false;
                        } else {
                            fileList.add(listFile[i]);

                        }
                    }
                }
            }
        }
        return fileList;
    }

    public void onPostExecute(ArrayList<File> list) {
        asyncTaskListener.IAmFinished(list);
    }
}
}

但我无法填充列表视图。 列表视图中没有显示任何内容。
我怎样才能解决这个问题？我究竟做错了什么？

Answer 1

从onCreate中删除以下行。

IAmFinished(fileList);

从onCreate剪切以下行并在for循环后粘贴IamFinished。

lv.setAdapter(new ArrayAdapter<>(this,
        android.R.layout.simple_list_item_1, name));

并且不要忘记声明JazzyListView全球。

修改代码的结尾。

    public interface IAsyncTask {

    ArrayList<String> IAmFinished(ArrayList<File> arrayList);
}

public class MainActivity2 extends AppCompatActivity implements IAsyncTask {


public static ArrayList<File> fileList = new ArrayList<>();
public static ArrayList<String> name = new ArrayList<>();
Longoperation longoperation;
JazzyListView lv;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main2);

    File dir1 = new File(Environment.getExternalStorageDirectory().getPath());
    longoperation = new Longoperation(dir1, this);
    longoperation.execute();
    lv = (JazzyListView) findViewById(R.id.list);



}

@Override
public ArrayList<String> IAmFinished(ArrayList<File> list) {
    for(int i=0;i< list.size();i++){
        name.add(list.get(i).getName());
    }

        lv.setAdapter(new ArrayAdapter<>(this,
            android.R.layout.simple_list_item_1, name));
    return name;
}

private class Longoperation extends AsyncTask<File, Void, ArrayList<File>>{

    File dir;
    private static final String TAG = "com.example.dell_1.myapp3.Zip";
    private IAsyncTask asyncTaskListener;

    public Longoperation(File dir,IAsyncTask asyncTaskListener) {
        this.dir = dir;
        this.asyncTaskListener = asyncTaskListener;
    }

    @Override
    protected ArrayList<File> doInBackground(File... params) {
        File listFile[] = dir.listFiles();
        if (listFile != null && listFile.length > 0) {
            for (int i = 0; i < listFile.length; i++) {

                if (listFile[i].isDirectory()) {
                    doInBackground(listFile[i]);

                } else {

                    boolean booleanpdf = false;
                    if (listFile[i].getName().endsWith(".zip") || listFile[i].getName().endsWith(".jar")) {

                        for (int j = 0; j < fileList.size(); j++) {
                            if (fileList.get(j).getName().equals(listFile[i].getName())) {
                                booleanpdf = true;
                            } else {

                            }
                        }

                        if (booleanpdf) {
                            booleanpdf = false;
                        } else {
                            fileList.add(listFile[i]);

                        }
                    }
                }
            }
        }
        return fileList;
    }

    public void onPostExecute(ArrayList<File> list) {
        asyncTaskListener.IAmFinished(list);
    }
}
}

Answer 2

您需要通过调用notifyDataSetChanged()来刷新适配器。像这样：

lv = (JazzyListView) findViewById(R.id.list);
..
lv.getAdapter().notifyDataSetChanged();

或者您可以使用以下内容：

// need to make the class scope variable.
ArrayAdapter mAdapter;

// create the adapter
mAdapter = new ArrayAdapter<>(this,
        android.R.layout.simple_list_item_1, name)
lv.setAdapter(adapter);

...
// refresh the adapter in your listener.
mAdapter.notifyDataSetChanged()

从Asynctask返回arraylist

2 个答案: