Android：自定义 ArrayList 不起作用

Question

我从三天开始就一直在搜索这个问题。请帮忙！

我正在尝试在AsynTask中创建自定义ArrayList，但不在乎，因为它在外部也不起作用。

首先我使用了setListAdapter，但它没有为我的类定义，甚至我的类也扩展了ListActivity。然后，我尝试使用ListView setAdapter，但它始终返回nullpointerexception。

这是我的第一个代码：

package Comments;
import java.util.ArrayList;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.Window;
import android.view.WindowManager;
import android.widget.ListView;
import android.widget.Toast;
import com.example.helloandroid.R;
import com.example.podcastq.ListActivity;
public class PrepareComments extends ListActivity {
static String titulo;
static String parentid;
static Context contexto;
static ArrayList<String> resultado;
ListView lv;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
            WindowManager.LayoutParams.FLAG_FULLSCREEN);
    setContentView(R.layout.buscar_listview);
}
public PrepareComments(Context contexto) {
    super();
    PrepareComments.contexto=contexto;
}

public void SetParams(String titulo, String parentid) {
    PrepareComments.titulo = titulo;
    PrepareComments.parentid = parentid;
}

public void ShowComments() {
    new AsyncTaskSearchName().execute(titulo, parentid);
}
private class AsyncTaskSearchName
extends
AsyncTask<String, String, SubmitResponseResult> {
    ProgressDialog dialog;

    @Override
    protected void onPreExecute() {
        try {
            dialog = new ProgressDialog(PrepareComments.contexto);
            dialog.setTitle(R.string.cargando);
            dialog.setMessage(PrepareComments.contexto.getString(R.string.obtInfoServer));
            dialog.setCancelable(false);
            dialog.show();
        } catch (final Exception e) {
            runOnUiThread(new Runnable() {
                public void run() {
                    Toast.makeText(PrepareComments.contexto, e.getMessage(),Toast.LENGTH_SHORT).show();
                    Log.e("ERROR", e.getStackTrace().toString());
                }
            });
        }
    }
    @Override
    protected SubmitResponseResult doInBackground(String... strings) {
        JoomlaServices oc = new JoomlaServices();
        try {
            SubmitResponseResult sr = oc.getComments(PrepareComments.titulo);
            PrepareComments.resultado = sr.getResult();
            PrepareComments.parentid = sr.getId();
        }  catch (final Exception e) {
            runOnUiThread(new Runnable() {
                public void run() {
                    Toast.makeText(PrepareComments.contexto,PrepareComments.contexto.getString(R.string.connectionError), Toast.LENGTH_SHORT).show();
                    Log.e("ERROR", e.getCause().toString());
                }
            });
        }
        return null;
    }
    @Override
    protected void onProgressUpdate(String... responses) {
        runOnUiThread(new Runnable() {
            public void run() {
                try {
                    ListView lv = (ListView) findViewById(android.R.id.list); //NULLPOINTEREXCEPTION IN THIS LINE!!
                    ListViewSuggestionAdapter lvSuggestionAdapt = new ListViewSuggestionAdapter(
                            PrepareComments.contexto, R.layout.listview_item_left, PrepareComments.resultado);  
                    lv.setAdapter(lvSuggestionAdapt);
                } catch (Exception e) {
                    Log.i("MI_ERROR", e.getMessage());
                }
            }
        });
    }
    @Override
    protected void onPostExecute(final SubmitResponseResult result) {
        runOnUiThread(new Runnable() {
            public void run() {
                try {
                    dialog.dismiss();
                } catch (Exception e) {
                    Log.i("MI_ERROR", e.getMessage());
                }
            }
        });
    }
}
}

有以下几行的问题：

ListView lv = (ListView) findViewById(android.R.id.list); //NULLPOINTEREXCEPTION IN THIS LINE!!
                    ListViewSuggestionAdapter lvSuggestionAdapt = new ListViewSuggestionAdapter(
                            PrepareComments.contexto, R.layout.listview_item_left, PrepareComments.resultado);  
                    lv.setAdapter(lvSuggestionAdapt);

这是我的第二个代码：

package Comments;
import java.util.ArrayList;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.Window;
import android.view.WindowManager;
import android.widget.ListView;
import android.widget.Toast;
import com.example.helloandroid.R;
import com.example.podcastq.ListActivity;
public class PrepareComments extends ListActivity {
static String titulo;
static String parentid;
static Context contexto;
static ArrayList<String> resultado;
ListView lv;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
            WindowManager.LayoutParams.FLAG_FULLSCREEN);
    setContentView(R.layout.buscar_listview);
}
public PrepareComments(Context contexto) {
    super();
    PrepareComments.contexto=contexto;
}

public void SetParams(String titulo, String parentid) {
    PrepareComments.titulo = titulo;
    PrepareComments.parentid = parentid;
}

public void ShowComments() {
    new AsyncTaskSearchName().execute(titulo, parentid);
}
private class AsyncTaskSearchName
extends
AsyncTask<String, String, SubmitResponseResult> {
    ProgressDialog dialog;

    @Override
    protected void onPreExecute() {
        try {
            dialog = new ProgressDialog(PrepareComments.contexto);
            dialog.setTitle(R.string.cargando);
            dialog.setMessage(PrepareComments.contexto.getString(R.string.obtInfoServer));
            dialog.setCancelable(false);
            dialog.show();
        } catch (final Exception e) {
            runOnUiThread(new Runnable() {
                public void run() {
                    Toast.makeText(PrepareComments.contexto, e.getMessage(),Toast.LENGTH_SHORT).show();
                    Log.e("ERROR", e.getStackTrace().toString());
                }
            });
        }
    }
    @Override
    protected SubmitResponseResult doInBackground(String... strings) {
        JoomlaServices oc = new JoomlaServices();
        try {
            SubmitResponseResult sr = oc.getComments(PrepareComments.titulo);
            PrepareComments.resultado = sr.getResult();
            PrepareComments.parentid = sr.getId();

        }  catch (final Exception e) {
            runOnUiThread(new Runnable() {
                public void run() {
                    Toast.makeText(PrepareComments.contexto,PrepareComments.contexto.getString(R.string.connectionError), Toast.LENGTH_SHORT).show();
                    Log.e("ERROR", e.getCause().toString());
                }
            });
        }
        return null;
    }
    @Override
    protected void onProgressUpdate(String... responses) {
        runOnUiThread(new Runnable() {
            public void run() {
                try {
                                       ListViewSuggestionAdapter lvSuggestionAdapt = new ListViewSuggestionAdapter(
                            PrepareComments.contexto, R.layout.listview_item_left, PrepareComments.resultado);  
                                            PrepareComments.setListAdapter(lvSuggestionAdapt); //UNDEFINED FUNCTION FOR PREPARECOMMENTS IN THIS LINE
                } catch (Exception e) {
                    Log.i("MI_ERROR", e.getMessage());
                }
            }
        });
    }
    @Override
    protected void onPostExecute(final SubmitResponseResult result) {
        runOnUiThread(new Runnable() {
            public void run() {
                try {
                    dialog.dismiss();
                } catch (Exception e) {
                    Log.i("MI_ERROR", e.getMessage());
                }
            }
        });
    }
}
}

有以下几行的问题：

ListViewSuggestionAdapter lvSuggestionAdapt = new ListViewSuggestionAdapter(
                            PrepareComments.contexto, R.layout.listview_item_left, PrepareComments.resultado);  
                                                PrepareComments.setListAdapter(lvSuggestionAdapt); //UNDEFINED FUNCTION FOR PREPARECOMMENTS IN THIS LINE

我的 xml 列表视图定义是：

<ListView
            android:id="@android:id/list"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentLeft="true"
            android:layout_alignParentTop="true"
            android:clickable="false"
            android:longClickable="false" >
        </ListView>

谢谢！

编辑：日志猫

01-31 22:10:08.995: E/AndroidRuntime(283): FATAL EXCEPTION: main
01-31 22:10:08.995: E/AndroidRuntime(283): java.lang.NullPointerException
01-31 22:10:08.995: E/AndroidRuntime(283):  at Comments.PrepareComments$AsyncTaskSearchName$3.run(PrepareComments.java:141)
01-31 22:10:08.995: E/AndroidRuntime(283):  at android.os.Handler.handleCallback(Handler.java:587)
01-31 22:10:08.995: E/AndroidRuntime(283):  at android.os.Handler.dispatchMessage(Handler.java:92)
01-31 22:10:08.995: E/AndroidRuntime(283):  at android.os.Looper.loop(Looper.java:123)
01-31 22:10:08.995: E/AndroidRuntime(283):  at android.app.ActivityThread.main(ActivityThread.java:4627)
01-31 22:10:08.995: E/AndroidRuntime(283):  at java.lang.reflect.Method.invokeNative(Native Method)
01-31 22:10:08.995: E/AndroidRuntime(283):  at java.lang.reflect.Method.invoke(Method.java:521)
01-31 22:10:08.995: E/AndroidRuntime(283):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
01-31 22:10:08.995: E/AndroidRuntime(283):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
01-31 22:10:08.995: E/AndroidRuntime(283):  at dalvik.system.NativeStart.main(Native Method)

Answer 1

使用

ListView lv = (ListView)PrepareComments.this.findViewById(android.R.id.list);

而不是

ListView lv = (ListView) findViewById(android.R.id.list);

在进度更新中使用列表视图初始化lv

注意：无需在onPreExecute和onPostExecute中使用runOnUiThread，因为这些方法在UI线程上调用，那么我们可以在不使用runOnUiThread的情况下访问或更新UI元素