当用户没有选择任何选项时，如何防止微调器选择第一项？

Question

当我运行应用程序时，它会直接选择第一项，然后将意图调用到GoogleMap，即使用户尚未选择任何选项。如何防止这种情况？以下是部分代码...谢谢

MainActivity.java

final ArrayList<Country> countries = new ArrayList<Country>();
countries.add(new Country("Malaysia", R.drawable.malaysia));
countries.add(new Country("Korea", R.drawable.south_korea));
countries.add(new Country("Argentina", R.drawable.argentina));
countries.add(new Country("Australia", R.drawable.australia));
countries.add(new Country("Japan", R.drawable.japan));
countries.add(new Country("United Kingdom", R.drawable.united_kingdom));

customSpinner = (Spinner)findViewById(R.id.custom_spinner);
SpinnerAdapter adapter = new SpinnerAdapter(this, countries);
customSpinner.setAdapter(adapter);
customSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
        Intent intent = new Intent(Intent.ACTION_VIEW);

        switch (position) {
            case 0:
                intent.setData(Uri.parse("geo:4.213155, 103.402914"));
                break;
            case 1:
                intent.setData(Uri.parse("geo:36.593562, 127.040436"));
                break;
            case 2:
                intent.setData(Uri.parse("geo:-34.883324, -65.140799"));
                break;
            case 3:
                intent.setData(Uri.parse("geo:-24.372645, 131.823709"));
                break;
            case 4:
                intent.setData(Uri.parse("geo:36.875761, 138.729092"));
                break;
            case 5:
                intent.setData(Uri.parse("geo:54.887410, -2.913750"));
                break;
        }

        if (intent.resolveActivity(getPackageManager()) != null)
                startActivity(intent);
        }
    }

SpinnerAdapter.java

public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        View spinnerItem = convertView;

        if(spinnerItem == null){
            LayoutInflater inflater = (LayoutInflater) getContext().getSystemService(getContext().LAYOUT_INFLATER_SERVICE);
            spinnerItem = inflater.inflate(R.layout.spinner_rows, parent, false);
            //spinnerItem = LayoutInflater.from(getContext()).inflate(R.layout.spinner_rows, parent, false);
        }

        Country tempCountry = (Country) getItem(position);

        ImageView image = (ImageView) spinnerItem.findViewById(R.id.imageView);
        TextView text = (TextView) spinnerItem.findViewById(R.id.textView);

        image.setImageResource(tempCountry.getCountryImage());
        image.setVisibility(View.VISIBLE);
        text.setText(tempCountry.getCountryName());

        return spinnerItem;
    }

    @Override
    public View getDropDownView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        return getView(position, convertView, parent);
    }

Answer 1

请在您的 MainActivity 中使用此代码，同时设置适配器会对您有所帮助。

  SpinnerAdapter adapter = new SpinnerAdapter(this, countries) {

        @Override
        public boolean isEnabled(int position) {

            if (position == 0) {
                return false;
            }
            return true;

        }
    };
    customSpinner.setAdapter(adapter);

Answer 2

将此添加到您的代码中

countries.add(new Country("Select country", -1));

将此添加到您的适配器

if (tempCountry.getCountryImage() !=  -1 ){
    image.setImageResource(tempCountry.getCountryImage());
    image.setVisibility(View.VISIBLE);
}else{
    image.setVisibility(View.GONE);
}

您的案例以case 1开头

Answer 3

please try below code...

final ArrayList<Country> countries = new ArrayList<Country>();
    countries.add(new Country("Select Country", R.drawable.country_icon));
    countries.add(new Country("Malaysia", R.drawable.malaysia));
    countries.add(new Country("Korea", R.drawable.south_korea));
    countries.add(new Country("Argentina", R.drawable.argentina));
    countries.add(new Country("Australia", R.drawable.australia));
    countries.add(new Country("Japan", R.drawable.japan));
    countries.add(new Country("United Kingdom", R.drawable.united_kingdom));

    customSpinner = (Spinner)findViewById(R.id.custom_spinner);
    SpinnerAdapter adapter = new SpinnerAdapter(this, countries);
    customSpinner.setAdapter(adapter);
    customSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            Intent intent = new Intent(Intent.ACTION_VIEW);

            switch (position) {
                case 0:
                break;
                case 1:
                    intent.setData(Uri.parse("geo:4.213155, 103.402914"));
                    break;
                case 2:
                    intent.setData(Uri.parse("geo:36.593562, 127.040436"));
                    break;
                case 3:
                    intent.setData(Uri.parse("geo:-34.883324, -65.140799"));
                    break;
                case 4:
                    intent.setData(Uri.parse("geo:-24.372645, 131.823709"));
                    break;
                case 5:
                    intent.setData(Uri.parse("geo:36.875761, 138.729092"));
                    break;
                case 6:
                    intent.setData(Uri.parse("geo:54.887410, -2.913750"));
                    break;
            }

            if (position!=0 && intent.resolveActivity(getPackageManager()) != null)
                    startActivity(intent);
            }
        }

Answer 4

您好，这可能有点晚了，但我有一个适合我的简单解决方案。 我为任何微调器创建了一个开关。

所以我设置了一个变量 int spinnerSwitch;。 然后在onCreate我将开关设置为spinnerSwitch = 1;

然后

@Override
        public void onItemSelected(AdapterView<?> parent, View view
                , int position, long id) {
            String itemText = parent.getItemAtPosition(position).toString();
            Log.i(TAG, "Selected: " + itemText );
            if(spinnerCitySwitch == 1){
                spinnerCitySwitch = 0;
                return;
            }
            //Then you can write your code here
             
        }

所以当我的活动被创建时，微调器会自动选择列表中的任何项目。我敢肯定那里有很多奇特的解决方法，但这对我有用……现在。

Answer 5

在MainActivity.java 中引入一个布尔变量boolean isFirstTime = true; 在onItemSelected() 方法中添加这一行：

public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
//If the Spinner's item is selected for the first time then return and make 
//isFirstTime to false, so when the user select it for the second time (as user is 
//always second) the spinner will work fine.
                if(isFirstTime){
                    isFirstTime = false;
                    return;
                }
... }

但是，当用户选择第一个选项时，android 不会调用 onItemSelected() 方法 因此，您必须制作一个自定义微调器，即使该项目被第二次选中，它也会调用 onItemSelected()

public class CustomSpinner extends android.support.v7.widget.AppCompatSpinner {

    private int lastPosition = 0;

//overrite the required constructors
...
//

//In android Spinners, when an item is selected for the second time then android does not call onItemSelected () method
//However, when an item is selected, the setSelection method will always be triggered
// So in this method, we record and check the last selection position. If they are the same, just call the monitor manually
    
@Override
    public void setSelection(int position, boolean animate) {
        super.setSelection(position, animate);
        if (position == lastPosition){
            getOnItemSelectedListener().onItemSelected(this,null,position,0);
        }
        lastPosition = position;
    }

    @Override
    public void setSelection(int position) {
        super.setSelection(position);
        if (position == lastPosition){
            getOnItemSelectedListener().onItemSelected(this,null,position,0);
        }
        lastPosition = position;
    }
}

Answer 6

使列表的第一个选择为空。

String selecteditem="";
 
if (selecteditem.isEmpty())
{

}else{
    // do work
}