我想过一些不那么优雅的方法来解决这个问题,但我知道我一定遗漏了什么。
我的onItemSelected立即启动,没有与用户进行任何交互,这是不希望的行为。我希望UI能够等到用户选择某样东西后再执行任何操作。
我甚至尝试在onResume()中设置监听器,希望能有所帮助,但它没有。
我怎样才能阻止它在用户可以触摸控件之前发射?
public class CMSHome extends Activity {
private Spinner spinner;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// Heres my spinner ///////////////////////////////////////////
spinner = (Spinner) findViewById(R.id.spinner);
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
this, R.array.pm_list, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(adapter);
};
public void onResume() {
super.onResume();
spinner.setOnItemSelectedListener(new MyOnItemSelectedListener());
}
public class MyOnItemSelectedListener implements OnItemSelectedListener {
public void onItemSelected(AdapterView<?> parent,
View view, int pos, long id) {
Intent i = new Intent(CMSHome.this, ListProjects.class);
i.putExtra("bEmpID", parent.getItemAtPosition(pos).toString());
startActivity(i);
Toast.makeText(parent.getContext(), "The pm is " +
parent.getItemAtPosition(pos).toString(), Toast.LENGTH_LONG).show();
}
public void onNothingSelected(AdapterView parent) {
// Do nothing.
}
}
}
不幸的是,解决这个问题的两个最常见的建议解决方案,即统计回调发生次数和发布Runnable以在稍后设置回调,在启用可访问性选项时都可能失败。下面是一个帮助类,它可以解决这些问题。进一步的解释在评论区。
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.Spinner;
import android.widget.SpinnerAdapter;
/**
* Spinner Helper class that works around some common issues
* with the stock Android Spinner
*
* A Spinner will normally call it's OnItemSelectedListener
* when you use setSelection(...) in your initialization code.
* This is usually unwanted behavior, and a common work-around
* is to use spinner.post(...) with a Runnable to assign the
* OnItemSelectedListener after layout.
*
* If you do not call setSelection(...) manually, the callback
* may be called with the first item in the adapter you have
* set. The common work-around for that is to count callbacks.
*
* While these workarounds usually *seem* to work, the callback
* may still be called repeatedly for other reasons while the
* selection hasn't actually changed. This will happen for
* example, if the user has accessibility options enabled -
* which is more common than you might think as several apps
* use this for different purposes, like detecting which
* notifications are active.
*
* Ideally, your OnItemSelectedListener callback should be
* coded defensively so that no problem would occur even
* if the callback was called repeatedly with the same values
* without any user interaction, so no workarounds are needed.
*
* This class does that for you. It keeps track of the values
* you have set with the setSelection(...) methods, and
* proxies the OnItemSelectedListener callback so your callback
* only gets called if the selected item's position differs
* from the one you have set by code, or the first item if you
* did not set it.
*
* This also means that if the user actually clicks the item
* that was previously selected by code (or the first item
* if you didn't set a selection by code), the callback will
* not fire.
*
* To implement, replace current occurrences of:
*
* Spinner spinner =
* (Spinner)findViewById(R.id.xxx);
*
* with:
*
* SpinnerHelper spinner =
* new SpinnerHelper(findViewById(R.id.xxx))
*
* SpinnerHelper proxies the (my) most used calls to Spinner
* but not all of them. Should a method not be available, use:
*
* spinner.getSpinner().someMethod(...)
*
* Or just add the proxy method yourself :)
*
* (Quickly) Tested on devices from 2.3.6 through 4.2.2
*
* @author Jorrit "Chainfire" Jongma
* @license WTFPL (do whatever you want with this, nobody cares)
*/
public class SpinnerHelper implements OnItemSelectedListener {
private final Spinner spinner;
private int lastPosition = -1;
private OnItemSelectedListener proxiedItemSelectedListener = null;
public SpinnerHelper(Object spinner) {
this.spinner = (spinner != null) ? (Spinner)spinner : null;
}
public Spinner getSpinner() {
return spinner;
}
public void setSelection(int position) {
lastPosition = Math.max(-1, position);
spinner.setSelection(position);
}
public void setSelection(int position, boolean animate) {
lastPosition = Math.max(-1, position);
spinner.setSelection(position, animate);
}
public void setOnItemSelectedListener(OnItemSelectedListener listener) {
proxiedItemSelectedListener = listener;
spinner.setOnItemSelectedListener(listener == null ? null : this);
}
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
if (position != lastPosition) {
lastPosition = position;
if (proxiedItemSelectedListener != null) {
proxiedItemSelectedListener.onItemSelected(
parent, view, position, id
);
}
}
}
public void onNothingSelected(AdapterView<?> parent) {
if (-1 != lastPosition) {
lastPosition = -1;
if (proxiedItemSelectedListener != null) {
proxiedItemSelectedListener.onNothingSelected(
parent
);
}
}
}
public void setAdapter(SpinnerAdapter adapter) {
if (adapter.getCount() > 0) {
lastPosition = 0;
}
spinner.setAdapter(adapter);
}
public SpinnerAdapter getAdapter() { return spinner.getAdapter(); }
public int getCount() { return spinner.getCount(); }
public Object getItemAtPosition(int position) { return spinner.getItemAtPosition(position); }
public long getItemIdAtPosition(int position) { return spinner.getItemIdAtPosition(position); }
public Object getSelectedItem() { return spinner.getSelectedItem(); }
public long getSelectedItemId() { return spinner.getSelectedItemId(); }
public int getSelectedItemPosition() { return spinner.getSelectedItemPosition(); }
public void setEnabled(boolean enabled) { spinner.setEnabled(enabled); }
public boolean isEnabled() { return spinner.isEnabled(); }
}
只是为了补充使用onTouchListener来区分对setOnItemSelectedListener的自动调用(这是Activity初始化的一部分,等等)与实际用户交互触发的对它的调用之间的提示,在尝试了其他一些建议后,我做了以下工作,并发现它用最少的代码行就能很好地工作。
只需要为你的Activity/Fragment设置一个布尔字段:
private Boolean spinnerTouched = false;
然后在你设置你的旋转器的setOnItemSelectedListener之前,设置一个onTouchListener:
spinner.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
System.out.println("Real touch felt.");
spinnerTouched = true;
return false;
}
});
spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
...
if (spinnerTouched){
//Do the stuff you only want triggered by real user interaction.
}
spinnerTouched = false;
我找到了更优雅的解决方法。它包括计算ArrayAdapter(在您的例子中是“适配器”)被调用的次数。假设你有一个转轮,你调用:
int iCountAdapterCalls = 0;
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
this, R.array.pm_list, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(adapter);
在onCreate之后声明一个int计数器,然后在onItemSelected()方法内部放置一个“if”条件来检查atapter被调用了多少次。在你的例子中,你只调用了一次:
if(iCountAdapterCalls < 1)
{
iCountAdapterCalls++;
//This section executes in onCreate, during the initialization
}
else
{
//This section corresponds to user clicks, after the initialization
}
我有很多问题与旋转发射时,我不想,所有的答案在这里是不可靠的。它们确实有效——但只是有时有效。您最终会遇到它们失败并将错误引入代码的情况。
对我来说,有效的方法是将最后选中的索引存储在一个变量中,并在侦听器中对其求值。如果它与新选定的索引相同,则不做任何操作并返回,否则继续使用侦听器。这样做:
//Declare a int member variable and initialize to 0 (at the top of your class)
private int mLastSpinnerPosition = 0;
//then evaluate it in your listener
@Override
public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
if(mLastSpinnerPosition == i){
return; //do nothing
}
mLastSpinnerPosition = i;
//do the rest of your code now
}
相信我,这是目前为止最可靠的解决方案。一个黑客,但它工作!