Question

我正在解析从API检索的数据，然后在列表视图中显示它。我还包括了一个swipeToRefreshLayout。我希望列表每2秒后自动更新一次信息。

错误::尝试在空对象引用上调用虚方法'java.io.File android.content.Context.getCacheDir（）' 这个错误就在这一行 -

RequestQueue requestQueue = Volley.newRequestQueue（this）;

我对处理程序了解不多。我想我没有在正确的地方使用它。

以下是完整的代码：

public class BitbnsPrice extends AppCompatActivity {

private TextView mtv1;
private ListView list;
ArrayList<String> price=null;
private int mInterval = 5000;
private Handler mHandler;
private SwipeRefreshLayout swipe2refresh;


protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    swipe2refresh= (SwipeRefreshLayout) findViewById(R.id.swipe2refresh);
    swipe2refresh.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
        @Override
        public void onRefresh() {
            swipe2refresh.setRefreshing(true);
            DataFromExchange();
            swipe2refresh.setRefreshing(false);

        }
    });

    DataFromExchange();
    //ListView list=(ListView) findViewById(R.id.list);

}

public void updateList(ArrayList<String> price){
    ListView list= (ListView) findViewById(R.id.list) ;
    CoinAdapter adapter= new CoinAdapter(this,R.layout.coin_layout,price);
    list.setAdapter(adapter);
}

public  void DataFromExchange(){
    String URL="https://bitbns.com/order/getTickerAll";
    //////////below line is showing me the error after 3 second.
    RequestQueue requestQueue= Volley.newRequestQueue(this);
    JsonArrayRequest objreq = new JsonArrayRequest(
            Request.Method.GET,
            URL,
            null,
            new Response.Listener<JSONArray>() {
                @Override
                public void onResponse(JSONArray response) {
                    getDataFromExchange Getprice= new getDataFromExchange();
                    price= Getprice.getDataFromBitbnsExchange(response);
                    String str="";
                    for(String p : price)
                        str+=p + " ";
                    Log.e("price from API response" ,str);
                    //////////////////////////////////////////////////////
                    updateList(price);

                }
            },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    Log.e("error response" ,error.toString());
                    Toast.makeText(BitbnsPrice.this," Network error", Toast.LENGTH_LONG).show();

                }
            }

    );

    requestQueue.add(objreq);

    final Handler handler = new Handler();

    Runnable refresh = new Runnable() {
        @Override
        public void run() {
            new BitbnsPrice().DataFromExchange();
            handler.postDelayed(this, 3 * 1000);
        }
    };

    handler.postDelayed(refresh, 3 * 1000);
}

}

Answer 1

我将处理程序放在一个不同的函数中，然后我从onCreate方法调用它并且它有效。

这是更改的代码。这完全没问题。

private final Handler handler = new Handler();

private void doTheAutoRefresh() {
    handler.postDelayed(new Runnable() {
        @Override
        public void run() {
            DataFromExchange();
            doTheAutoRefresh();
        }
    }, 2000);
}

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    doTheAutoRefresh(); //// added code

    swipe2refresh= (SwipeRefreshLayout) findViewById(R.id.swipe2refresh);
    swipe2refresh.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
        @Override
        public void onRefresh() {
            swipe2refresh.setRefreshing(true);
            DataFromExchange();
            swipe2refresh.setRefreshing(false);

        }
    });

    DataFromExchange();
    //ListView list=(ListView) findViewById(R.id.list);

}

我希望此活动每3秒后自动刷新一次，但它给了我错误

1 个答案: