java - float 操作按钮 android

Question

有人可以帮助我吗？当我按下 FloatingActionButton 时， Activity 将关闭并返回。我做错了什么？

    public class Regolamento extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_regolamento);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "English", Snackbar.LENGTH_LONG);
                TextView tv = (TextView) findViewById(R.id.text);
                tv.setText("ciao");

            }
        });
    }}

<androidx.core.widget.NestedScrollView
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        tools:context=".Regolamento"
        tools:showIn="@layout/activity_regolamento">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="@dimen/text_margin"
            android:text="wow"/>
    </androidx.core.widget.NestedScrollView>

我该怎么办？有人能帮我吗？直到一切正常之前突然停止工作

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference at com.example.bbmarinablu.Regolamento$1.onClick(Regolamento.java:29) at android.view.View.performClick(Unknown Source:17) at android.view.View.performClickInternal(Unknown Source:3) at android.view.View.access$3500(Unknown Source:0) at android.view.View$PerformClick.run(Unknown Source:8) at android.os.Handler.handleCallback(Unknown Source:2) at android.os.Handler.dispatchMessage(Unknown Source:4) at android.os.Looper.loop(Unknown Source:242) at android.app.ActivityThread.main(Unknown Source:98) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(Unknown Source:11) at com.android.internal.os.ZygoteInit.main(Unknown Source:275)

Answer 1

您需要在activity_regolamento.xml中定义id text。

在 TextView 元素中添加 android:id="@+id/text"。