Button.setOnLongClickListener失效：单击显示默认Toast长按不显示自定义Toast

想要实现按钮单击显示默认Toast、长按显示自定义Toast的功能，但目前程序启动就崩溃，自定义Toast无法触发，默认Toast也无法正常显示。

相关代码 #

MainActivity.kt #

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        btntoste.setOnClickListener {
            Toast.makeText(this,"this is defult toaste",Toast.LENGTH_SHORT)
        }
        btntoste.setOnLongClickListener {
            Toast(this).apply {
                duration = Toast.LENGTH_LONG
                view = layoutInflater.inflate(R.layout.custom_toaste, layconstrain)
                show()
            }
        }
    }
}

activity_main.xml #

<androidx.constraintlayout.widget.ConstraintLayout 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"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/btntoste"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Show Toste"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.266"
        android:backgroundTint="@color/material_dynamic_neutral50"
        android:textColor="@color/white"/>
</androidx.constraintlayout.widget.ConstraintLayout>

自定义Toast布局 custom_toaste.xml #

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/layconstrain"
    android:padding="16dp"
    android:background="@color/material_dynamic_neutral70">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:src="@drawable/ic_baseline_circle_notifications_24"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/txtcucont"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:text="Hay this is custom toaste"
        android:textSize="15sp"
        android:textColor="@color/purple_700"
        app:layout_constraintBottom_toBottomOf="@+id/imageView"
        app:layout_constraintStart_toEndOf="@+id/imageView"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.583" />
</androidx.constraintlayout.widget.ConstraintLayout>

Logcat错误信息 #

failed to add asset path /data/app/com.sumita.toaste-wg1Yd4-KC7e1sn36eDPchA==/base.apk
2023-05-10 11:58:44.858 18737-18737 ResourcesManager        pid-18737                            E  failed to add asset path /data/app/com.sumita.toaste-wg1Yd4-KC7e1sn36eDPchA==/base.apk
2023-05-10 11:58:44.861 18737-18737 ResourcesManager        pid-18737                            E  failed to add asset path /data/app/com.sumita.toaste-wg1Yd4-KC7e1sn36eDPchA==/base.apk
2023-05-10 11:58:45.088  2461-2501  ActivityThread          com.sumita.toaste                    E  Failed to find provider info for cn.teddymobile.free.anteater.den.provider
2023-05-10 11:58:45.229  2461-2461  AndroidRuntime          com.sumita.toaste                    E  FATAL EXCEPTION: main
                                                                                                    Process: com.sumita.toaste, PID: 2461
                                                                                                    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sumita.toaste/com.sumita.toaste.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                                                        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2994)
                                                                                                        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3072)
                                                                                                        at android.app.ActivityThread.-wrap11(Unknown Source:0)
                                                                                                        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1766)
                                                                                                        at android.os.Handler.dispatchMessage(Handler.java:106)
                                                                                                        at android.os.Looper.loop(Looper.java:214)
                                                                                                        at android.app.ActivityThread.main(ActivityThread.java:6977)
                                                                                                        at java.lang.reflect.Method.invoke(Native Method)
                                                                                                        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:528)
                                                                                                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:910)
                                                                                                    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                                                        at com.sumita.toaste.MainActivity.onCreate(MainActivity.kt:17)
                                                                                                        at android.app.Activity.performCreate(Activity.java:7227)
                                                                                                        at android.app.Activity.performCreate(Activity.java:7218)
                                                                                                        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
                                                                                                        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2947)
                                                                                                        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3072) 
                                                                                                        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
                                                                                                        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1766) 
                                                                                                        at android.os.Handler.dispatchMessage(Handler.java:106) 
                                                                                                        at android.os.Looper.loop(Looper.java:214) 
                                                                                                        at android.app.ActivityThread.main(ActivityThread.java:6977) 
                                                                                                        at java.lang.reflect.Method.invoke(Native Method) 
                                                                                                        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:528) 
                                                                                                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:910) 

核心问题 #

1. 按钮实例为空：直接使用btntoste但未正确绑定视图，导致空指针异常，程序启动即崩溃，根本无法触发后续的点击/长按事件。
2. 默认Toast未调用show()：Toast.makeText()创建实例后未执行show()，所以默认Toast也不会显示。
3. 自定义Toast布局加载错误：inflate(R.layout.custom_toaste, layconstrain)中的layconstrain是自定义布局里的ID，此时尚未加载该布局，传入会导致空指针，且Toast的视图不需要指定父容器，应传null。
4. 长按事件未返回布尔值：setOnLongClickListener要求返回布尔值，用于标记事件是否被消费。

修复步骤 #

1. 绑定按钮视图 #

可以选择两种方式：

• 方式一：使用视图绑定（推荐）
  在模块的build.gradle中启用视图绑定：

  android {
      ...
      buildFeatures {
          viewBinding true
      }
  }
  

  然后在Activity中使用：

  val binding = ActivityMainBinding.inflate(layoutInflater)
  setContentView(binding.root)
  // 用binding.btntoste访问按钮
  

• 方式二：手动findViewById
  在setContentView后添加：

  val btntoste = findViewById<Button>(R.id.btntoste)
  

2. 修复默认Toast代码 #

添加show()方法：

Toast.makeText(this,"this is default toast",Toast.LENGTH_SHORT).show()

3. 修复自定义Toast布局加载 #

将inflate的第二个参数改为null：

view = layoutInflater.inflate(R.layout.custom_toaste, null)

4. 补全长按事件返回值 #

在长按事件的最后返回true，表示消费该事件：

true

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        
        // 手动绑定按钮视图
        val btntoste = findViewById<Button>(R.id.btntoste)
        
        btntoste.setOnClickListener {
            // 默认Toast添加show()
            Toast.makeText(this,"this is default toast",Toast.LENGTH_SHORT).show()
        }
        
        btntoste.setOnLongClickListener {
            Toast(this).apply {
                duration = Toast.LENGTH_LONG
                // 修复布局加载的父容器参数
                view = layoutInflater.inflate(R.layout.custom_toaste, null)
                show()
            }
            // 返回true表示消费长按事件
            true
        }
    }
}

内容的提问来源于stack exchange，提问作者Sumita Das