Java Can';t将setOnClickListener添加到导航抽屉中的按钮
我想在按下导航抽屉中的按钮时创建一个Java Can';t将setOnClickListener添加到导航抽屉中的按钮,java,android,Java,Android,我想在按下导航抽屉中的按钮时创建一个警报对话框。我在activity.java文件中的onCreate函数中编写了以下代码 Button chooseBuildings = findViewById(R.id.chooseBuilding); final String[] colors = {"red", "green", "blue", "black"}; chooseBuildings.setOnClickListener(new View.OnClickListener()
警报对话框
。我在activity.java文件中的onCreate
函数中编写了以下代码
Button chooseBuildings = findViewById(R.id.chooseBuilding);
final String[] colors = {"red", "green", "blue", "black"};
chooseBuildings.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
AlertDialog.Builder builder = new AlertDialog.Builder(StartNavigationActivity.this);
builder.setTitle("Choose a building");
builder.setItems(colors, new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
}
});
builder.show();
}
});
当检查我的logcat时,我得到一个NullPointerException
:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
这是我的menu.xml
文件:
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
>
<item
android:id="@+id/settings"
android:icon="@drawable/ic_settings"
android:title="Settings"
/>
<item
android:id="@+id/chooseBuilding"
android:icon="@drawable/ic_change_building"
android:title="Choose Building"
/>
<item
android:id="@+id/feedback"
android:title="Send Feedback"
android:icon="@drawable/ic_feedback"
/>
<item
android:id="@+id/help"
android:title="Help"
android:icon="@drawable/ic_help"
/>
</menu>
如何正确引用导航抽屉中的按钮以使事件侦听器工作?您不能以这种方式对菜单项使用ClickListener,但可以使用setNavigationItemSelectedListener: 首先在活动中实现侦听器:
public class YourActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener
然后,为导航抽屉设置侦听器:
NavigationView mNavigationView = findViewById(R.id.navigation view id);
mNavigationView.setNavigationItemSelectedListener(this);
最后,请观看以下活动:
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
switch (item.getItemId()) {
case R.id.chooseBuilding: {
AlertDialog.Builder builder = new AlertDialog.Builder(StartNavigationActivity.this);
builder.setTitle("Choose a building");
builder.setItems(colors, new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
}
});
builder.show();
}
}
return true;
}
您是否
实现了NavigationView.OnNavigationItemSelectedListener
?是否可以发布包含按钮R.id.chooseBuilding的xml?我已经添加了它。