Android类变量未及时赋值setOnItemSelectedListener
Android类变量未及时赋值setOnItemSelectedListener
提问于 2018-06-04 02:20:15
我正在编写一个货币转换器应用程序，并使用Volley请求向API发送请求以检索转换率。
我现在有两个旋转器(从货币和目标货币)。我有三个函数，一个用于将项添加到微调程序，一个用于在按下按钮时添加侦听器，另一个用于发送volley请求以检索JSON信息。
我相信我调用函数的顺序是正确的，但是似乎由于某种原因，toSpinnerText和fromSpinnerText的值没有被设置为微调函数的值。在我看来，它们应该在发送对url的请求之前设置，因为我在jsonSendRequest()之前调用了addItemsOnToSpinner()。但是当我调试日志调用时，当构造url字符串时，toSpinnerText和fromSpinnerText的值仍然是空字符串。
这是我到目前为止所拥有的。谢谢。
public class MainActivity extends AppCompatActivity {
RequestQueue rq;
Double conversionDouble;
Spinner toSpinner, fromSpinner;
String toSpinnerText = "";
String fromSpinnerText = "";
private Button convertBtn;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
addItemsOnToSpinner();
addListenerOnButton();
jsonSendRequest();
Button convertBtn = (Button) findViewById(R.id.convertBtn);
final EditText fromAmountEditText = findViewById(R.id.fromAmountEditText);
convertBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
TextView toAmountTextView = findViewById(R.id.toAmountTextView);
DecimalFormat percentageFormat = new DecimalFormat("0.00");
Double fromAmount = Double.parseDouble(fromAmountEditText.getText().toString());
String result = "$" + percentageFormat.format(conversionDouble*fromAmount);
toAmountTextView.setText(result);
}
});
rq = Volley.newRequestQueue(this);
}
public void jsonSendRequest() {
RequestQueue queue = Volley.newRequestQueue(this);
// String url = "http://free.currencyconverterapi.com/api/v3/convert?q=CAD_USD&compact=ultra";
String url = "http://free.currencyconverterapi.com/api/v3/convert?q=" + fromSpinnerText + "_" + toSpinnerText + "&compact=ultra";
// Request a string response
StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
JSONObject jsonobject = null;
try {
jsonobject = new JSONObject(response);
} catch (JSONException e) {
e.printStackTrace();
}
if (jsonobject.has(fromSpinnerText + "_" + toSpinnerText)) {
try {
conversionDouble = jsonobject.getDouble(fromSpinnerText + "_" + toSpinnerText);
// conversionDouble = jsonobject.getDouble(fromSpinnerText + "_" + toSpinnerText);
} catch (JSONException e) {
e.printStackTrace();
}
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
}
});
// Add the request to the RequestQueue.
queue.add(stringRequest);
}
public void addItemsOnToSpinner(){
Spinner toSpinner = (Spinner) findViewById(R.id.toSpinner);
Spinner fromSpinner = (Spinner) findViewById(R.id.fromSpinner);
List<String> currency = new ArrayList<String>();
currency.add("USD");
currency.add("CAD");
currency.add("CNY");
ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(
this, android.R.layout.simple_spinner_item, currency
);
dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
toSpinner.setAdapter(dataAdapter);
fromSpinner.setAdapter(dataAdapter);
fromSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
String fromSpinnerText = (String) parent.getItemAtPosition(position);
}
@Override
public void onNothingSelected(AdapterView<?> parent) {
}
});
toSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
String toSpinnerText = (String) parent.getItemAtPosition(position);
}
@Override
public void onNothingSelected(AdapterView<?> parent) {
}
});
}
public void addListenerOnButton() {
Spinner fromSpinner = (Spinner) findViewById(R.id.fromSpinner);
Spinner toSpinner = (Spinner) findViewById(R.id.toSpinner);
Button convertBtn = (Button) findViewById(R.id.convertBtn);
}
}回答 1
Stack Overflow用户
发布于 2018-06-04 02:23:43
如果你为它创建了一个新的局部变量，你将如何在fromSpinnerText中选择项。您将所选值存储到一个局部变量中，而不是在activity顶部创建的全局变量中。
替换
String fromSpinnerText = (String) parent.getItemAtPosition(position);至
fromSpinnerText = (String) parent.getItemAtPosition(position);并替换
String toSpinnerText = (String) parent.getItemAtPosition(position);至
toSpinnerText = (String) parent.getItemAtPosition(position);页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/50669590
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