当您调用异步任务的方法时，应用程序退出

Question

我有问题。我正在尝试创建 Activity 导致异步任务，并在执行调用的方法 adapterCreate() class Profile.class 后创建适配器。有必要在方法的第一个参数中传输上下文。在这里，例如如果我在class线上调用一个方法，一切正常，如果调用contex"this"。如果我从异步任务中调用，应用程序将退出。我不知道该怎么办。我希望得到你的帮助。谢谢！

Profile.class

public class Profile extends AppCompatActivity {



    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_application);

        new ParseTask(this).execute();

    }



public void adapterCreate(Activity context){

    String[] str1 = {"mesages1", "messages2"};
    String[] str2 = {"photo1", "photo2"};
    String[] str3 = {"name1", "name2"};

    adapter = new LazyAdapter(context, str1, str2, str3);
    list.setAdapter(adapter);

}

}

ParseTask.class

public class ParseTask extends AsyncTask<Void, Void, String> {

    HttpURLConnection urlConnection = null;
    BufferedReader reader = null;
    String resultJson = "";

    Activity act;

    public ParseTask (Activity context){
        this.act = context;
    }

    @Override
    protected String doInBackground(Void... params) {
        try {
            URL url = new URL("/friends.json");

            urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("GET");
            urlConnection.connect();

            InputStream inputStream = urlConnection.getInputStream();
            StringBuffer buffer = new StringBuffer();

            reader = new BufferedReader(new InputStreamReader(inputStream));

            String line;
            while ((line = reader.readLine()) != null) {
                buffer.append(line);
            }

            resultJson = buffer.toString();

        } catch (Exception e) {
            e.printStackTrace();
        }
        return resultJson;
    }

    @Override
    protected void onPostExecute(String strJson) {
        super.onPostExecute(strJson);

        new Profile().chatCreate();

    }
}

LazyAdapter.class

public class LazyAdapter extends BaseAdapter {

    private Activity activity;
    private String[] messages;
    private String[] photo;
    private String[] name;
    private static LayoutInflater inflater=null;
    //public ImageLoader imageLoader;

    public LazyAdapter(Activity a, String[] messages_c, String[] photo_c, String[] name_c) {
        activity = a;
        messages=messages_c;
        photo = photo_c;
        name = name_c;
        inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        //imageLoader=new ImageLoader(activity.getApplicationContext());
    }

    public int getCount() {
        return name.length;
    }

    public Object getItem(int position) {
        return position;
    }

    public long getItemId(int position) {
        return position;
    }

    public View getView(int position, View convertView, ViewGroup parent) {
        View vi=convertView;
        if(convertView==null) vi = inflater.inflate(R.layout.listview_row, null);

        TextView name_c = (TextView)vi.findViewById(R.id.name_c);
        TextView content_c = (TextView)vi.findViewById(R.id.content_c);
        ImageView image = (ImageView)vi.findViewById(R.id.image);
        name_chat.setText(name[position]);
        content_chat.setText(messages[position]);
        return vi;
    }
}

logcat 日志

09-24 16:49:10.821 7969-7969/package E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.NullPointerException
    at package.Profile.chatCreate(Profile.java:645)
    at package.ParseTask.onPostExecute(ParseTask.java:108)
    at package.ParseTask.onPostExecute(ParseTask.java:21)
    at android.os.AsyncTask.finish(AsyncTask.java:631)
    at android.os.AsyncTask.access0(AsyncTask.java:177)
    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:4745)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:511)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
    at dalvik.system.NativeStart.main(Native Method)

Answer 1

当您在 activity 中说 this 时，会发送 activity 的上下文，但异步任务并非如此（此处 this 指的是异步任务本身）所以你必须做的是 yourActivity.this.

Answer 2

你绝对不能这样做：

    new Profile().chatCreate();

Profile 是一个 Activity，它是一个 Android 组件。您不能使用 new 自己实例化 Android 个组件。只有 Android 框架可以实例化 Android 组件，因为它们需要先设置 Context 才能使用。

如果要调用 Activity 上的方法，则需要使用 Android 框架已经创建的 Activity 实例。

当您调用异步任务的方法时，应用程序退出

When you call a method of asynchronous tasks, the application quits

java

android

android-context

android-activity