Question

当我按下导航抽屉内的按钮时，我想创建一个AlertDialog。我从我的activity.java文件的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，以便事件监听器正常工作？

Answer 1

您不能以这种方式将clicklistener用于菜单项，而可以使用setNavigationItemSelectedListener：

在您的活动中首先实现侦听器：

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，赶上事件：

@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;
}

无法将setOnClickListener添加到导航抽屉中的按钮

1 个答案: