Question

我想要显示Toast消息＆＃34;正在处理..请等待。＆＃34;在用户按下listview项目后进行一些处理。从lv.setOnItemClickListener调用时，AsyncTask不起作用（但是从button.setOnClickListener调用时有效）。

知道为什么吗？

MyActivity.java

public class MyActivity extends Activity {

    private static Context context;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.my_activity);
        context = this;

        ListView lv = (ListView) findViewById(R.id.listView);
        Button button = (Button) findViewById(R.id.btn);

        // this DOESN't show the waiting message while processing
        lv.setOnItemClickListener(new OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view,
            int position, long id) {
                new AsyncMsg(position).execute();
            }
        });

        // this shows the waiting message while processing 
        button.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                int position = 0; //first item
                new AsyncMsg(position).execute();
            }
        });
    }

    public static void showWaitMessage() {
        Toast.makeText(context, "Processing.. Please wait.", Toast.LENGTH_SHORT)
           .show();
    }
}

AsyncTask：AsyncMsg.java

public class AsyncMsg extends AsyncTask<Void, Void, Void> {
    public int position;

    public AsyncMsg(int position) {
        this.position = position;
    }

    public void onPreExecute() {
        MyActivity.showWaitMessage();
    }

    @Override
    protected Void doInBackground(Void... params) {
        // do some long process with position
    }

    public void onPostExecute() {
    }
}

Answer 1

为什么不尝试这个

public class AsyncMsg extends AsyncTask<Void, Void, Void> {
    public int position;
    Context context;
    public AsyncMsg(int position,Context con) {
        this.position = position;
        context =con;
    }

    public void onPreExecute() {
        Toast.makeText(context, "Processing.. Please wait.", Toast.LENGTH_SHORT)
           .show();
    }
   }

然后像这样打电话

 new AsyncMsg(position,context).execute();

Answer 2

在Toast.make（..）中用作上下文MyActivity.this。

从OnItemClickListener内部调用时，AsyncTask无法显示Toast消息

2 个答案: