在 Kotlin 中更改 TextView 的文本时出错 - Android
Getting error in changing the text of TextView in Kotlin - Android
我是 android 开发的新手（几个小时前才开始），我只是想看看我在尝试如何工作，例如单击按钮时 TextView 的文本应该更改，但应用程序崩溃时它到达那条线。任何人都可以建议我应该做哪些改变。
MainActivity.kt
package com.example.ruthvikapplication
import android.os.Bundle
import android.widget.Button
import android.widget.RatingBar
import android.widget.TextView
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val button1=findViewById<Button>(R.id.button)
val ratingBar1= findViewById<RatingBar>(R.id.ratingBar)
val title1= findViewById<TextView>(R.id.title)
button1.setOnClickListener{
Toast.makeText(this@MainActivity, "Your rating"+ratingBar1.rating.toString(), Toast.LENGTH_SHORT).show()
title1.text= "Thanks for rating!!" // app crashes here...
}
}
}
activity_main.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="match_parent"
android:layout_height="match_parent"
android:background="#00FFCC"
tools:context=".MainActivity">
<TextView
android:id="@+id/myTitle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:rotationX="33"
android:text="Please rate this app!!"
android:textColor="#FF0000"
android:textSize="34sp"
android:textStyle="bold|italic"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Rate"
app:backgroundTint="#FFC800"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="@+id/ratingBar"
app:layout_constraintTop_toBottomOf="@+id/myTitle" />
<RatingBar
android:id="@+id/ratingBar"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="10dp"
android:layout_marginRight="10dp"
android:background="#00FFCC"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toStartOf="@+id/button"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/myTitle"
tools:ignore="SpeakableTextPresentCheck" />
</androidx.constraintlayout.widget.ConstraintLayout>
控制台
09/25 21:43:43: Launching 'app' on Pixel 5 API 30.
Install successfully finished in 4 s 826 ms.
$ adb shell am start -n "com.example.ruthvikapplication/com.example.ruthvikapplication.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER
Connected to process 6745 on device 'Pixel_5_API_30 [emulator-5554]'.
Capturing and displaying logcat messages from application. This behavior can be disabled in the "Logcat output" section of the "Debugger" settings page.
D/NetworkSecurityConfig: No Network Security Config specified, using platform default
D/NetworkSecurityConfig: No Network Security Config specified, using platform default
D/libEGL: loaded /vendor/lib/egl/libEGL_emulation.so
D/libEGL: loaded /vendor/lib/egl/libGLESv1_CM_emulation.so
D/libEGL: loaded /vendor/lib/egl/libGLESv2_emulation.so
W/System: A resource failed to call close.
W/hvikapplicatio: Accessing hidden method Landroid/view/View;->computeFitSystemWindows(Landroid/graphics/Rect;Landroid/graphics/Rect;)Z (greylist, reflection, allowed)
W/hvikapplicatio: Accessing hidden method Landroid/view/ViewGroup;->makeOptionalFitsSystemWindows()V (greylist, reflection, allowed)
D/HostConnection: HostConnection::get() New Host Connection established 0xee45b910, tid 6768
D/HostConnection: HostComposition ext ANDROID_EMU_CHECKSUM_HELPER_v1 ANDROID_EMU_native_sync_v2 ANDROID_EMU_native_sync_v3 ANDROID_EMU_native_sync_v4 ANDROID_EMU_dma_v1 ANDROID_EMU_direct_mem ANDROID_EMU_host_composition_v1 ANDROID_EMU_host_composition_v2 ANDROID_EMU_vulkan ANDROID_EMU_deferred_vulkan_commands ANDROID_EMU_vulkan_null_optional_strings ANDROID_EMU_vulkan_create_resources_with_requirements ANDROID_EMU_YUV_Cache ANDROID_EMU_async_unmap_buffer ANDROID_EMU_vulkan_ignored_handles ANDROID_EMU_has_shared_slots_host_memory_allocator ANDROID_EMU_vulkan_free_memory_sync ANDROID_EMU_vulkan_shader_float16_int8 ANDROID_EMU_vulkan_async_queue_submit ANDROID_EMU_sync_buffer_data GL_OES_vertex_array_object GL_KHR_texture_compression_astc_ldr ANDROID_EMU_host_side_tracing ANDROID_EMU_async_frame_commands ANDROID_EMU_gles_max_version_2
W/OpenGLRenderer: Failed to choose config with EGL_SWAP_BEHAVIOR_PRESERVED, retrying without...
D/EGL_emulation: eglCreateContext: 0xee460760: maj 2 min 0 rcv 2
D/EGL_emulation: eglMakeCurrent: 0xee460760: ver 2 0 (tinfo 0xee7b43f0) (first time)
I/Gralloc4: mapper 4.x is not supported
D/HostConnection: createUnique: call
D/HostConnection: HostConnection::get() New Host Connection established 0xee461330, tid 6768
D/goldfish-address-space: allocate: Ask for block of size 0x100
D/goldfish-address-space: allocate: ioctl allocate returned offset 0x34dffc000 size 0x2000
D/HostConnection: HostComposition ext ANDROID_EMU_CHECKSUM_HELPER_v1 ANDROID_EMU_native_sync_v2 ANDROID_EMU_native_sync_v3 ANDROID_EMU_native_sync_v4 ANDROID_EMU_dma_v1 ANDROID_EMU_direct_mem ANDROID_EMU_host_composition_v1 ANDROID_EMU_host_composition_v2 ANDROID_EMU_vulkan ANDROID_EMU_deferred_vulkan_commands ANDROID_EMU_vulkan_null_optional_strings ANDROID_EMU_vulkan_create_resources_with_requirements ANDROID_EMU_YUV_Cache ANDROID_EMU_async_unmap_buffer ANDROID_EMU_vulkan_ignored_handles ANDROID_EMU_has_shared_slots_host_memory_allocator ANDROID_EMU_vulkan_free_memory_sync ANDROID_EMU_vulkan_shader_float16_int8 ANDROID_EMU_vulkan_async_queue_submit ANDROID_EMU_sync_buffer_data GL_OES_vertex_array_object GL_KHR_texture_compression_astc_ldr ANDROID_EMU_host_side_tracing ANDROID_EMU_async_frame_commands ANDROID_EMU_gles_max_version_2
I/Choreographer: Skipped 45 frames! The application may be doing too much work on its main thread.
I/OpenGLRenderer: Davey! duration=792ms; Flags=0, IntendedVsync=1872865754256, Vsync=1873615754226, OldestInputEvent=9223372036854775807, NewestInputEvent=0, HandleInputStart=1873628675300, AnimationStart=1873628792800, PerformTraversalsStart=1873630847400, DrawStart=1873631928700, SyncQueued=1873632253400, SyncStart=1873637319300, IssueDrawCommandsStart=1873637409900, SwapBuffers=1873651804500, FrameCompleted=1873663434900, DequeueBufferDuration=2445200, QueueBufferDuration=5067700, GpuCompleted=9223372034707292159,
D/CompatibilityChangeReporter: Compat change id reported: 147798919; UID 10121; state: ENABLED
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.ruthvikapplication, PID: 6745
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at com.example.ruthvikapplication.MainActivity.onCreate$lambda-0(MainActivity.kt:21)
at com.example.ruthvikapplication.MainActivity.$r8$lambda$dEE9GmU9yeAvvuQdJ131D5Xmycc(Unknown Source:0)
at com.example.ruthvikapplication.MainActivity$$ExternalSyntheticLambda0.onClick(Unknown Source:6)
at android.view.View.performClick(View.java:7448)
at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1119)
at android.view.View.performClickInternal(View.java:7425)
at android.view.View.access00(View.java:810)
at android.view.View$PerformClick.run(View.java:28305)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
I/Process: Sending signal. PID: 6745 SIG: 9
我认为 XML 中 TextView 的 ID 是 myTitle，这与您在 Kotlin 文件中使用的 ID 不同，即 title
尝试log.d("TextView", title1.toString());
检查确认
我是 android 开发的新手（几个小时前才开始），我只是想看看我在尝试如何工作，例如单击按钮时 TextView 的文本应该更改，但应用程序崩溃时它到达那条线。任何人都可以建议我应该做哪些改变。
MainActivity.kt
package com.example.ruthvikapplication
import android.os.Bundle
import android.widget.Button
import android.widget.RatingBar
import android.widget.TextView
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val button1=findViewById<Button>(R.id.button)
val ratingBar1= findViewById<RatingBar>(R.id.ratingBar)
val title1= findViewById<TextView>(R.id.title)
button1.setOnClickListener{
Toast.makeText(this@MainActivity, "Your rating"+ratingBar1.rating.toString(), Toast.LENGTH_SHORT).show()
title1.text= "Thanks for rating!!" // app crashes here...
}
}
}
activity_main.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="match_parent"
android:layout_height="match_parent"
android:background="#00FFCC"
tools:context=".MainActivity">
<TextView
android:id="@+id/myTitle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:rotationX="33"
android:text="Please rate this app!!"
android:textColor="#FF0000"
android:textSize="34sp"
android:textStyle="bold|italic"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Rate"
app:backgroundTint="#FFC800"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="@+id/ratingBar"
app:layout_constraintTop_toBottomOf="@+id/myTitle" />
<RatingBar
android:id="@+id/ratingBar"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="10dp"
android:layout_marginRight="10dp"
android:background="#00FFCC"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toStartOf="@+id/button"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/myTitle"
tools:ignore="SpeakableTextPresentCheck" />
</androidx.constraintlayout.widget.ConstraintLayout>
控制台
09/25 21:43:43: Launching 'app' on Pixel 5 API 30.
Install successfully finished in 4 s 826 ms.
$ adb shell am start -n "com.example.ruthvikapplication/com.example.ruthvikapplication.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER
Connected to process 6745 on device 'Pixel_5_API_30 [emulator-5554]'.
Capturing and displaying logcat messages from application. This behavior can be disabled in the "Logcat output" section of the "Debugger" settings page.
D/NetworkSecurityConfig: No Network Security Config specified, using platform default
D/NetworkSecurityConfig: No Network Security Config specified, using platform default
D/libEGL: loaded /vendor/lib/egl/libEGL_emulation.so
D/libEGL: loaded /vendor/lib/egl/libGLESv1_CM_emulation.so
D/libEGL: loaded /vendor/lib/egl/libGLESv2_emulation.so
W/System: A resource failed to call close.
W/hvikapplicatio: Accessing hidden method Landroid/view/View;->computeFitSystemWindows(Landroid/graphics/Rect;Landroid/graphics/Rect;)Z (greylist, reflection, allowed)
W/hvikapplicatio: Accessing hidden method Landroid/view/ViewGroup;->makeOptionalFitsSystemWindows()V (greylist, reflection, allowed)
D/HostConnection: HostConnection::get() New Host Connection established 0xee45b910, tid 6768
D/HostConnection: HostComposition ext ANDROID_EMU_CHECKSUM_HELPER_v1 ANDROID_EMU_native_sync_v2 ANDROID_EMU_native_sync_v3 ANDROID_EMU_native_sync_v4 ANDROID_EMU_dma_v1 ANDROID_EMU_direct_mem ANDROID_EMU_host_composition_v1 ANDROID_EMU_host_composition_v2 ANDROID_EMU_vulkan ANDROID_EMU_deferred_vulkan_commands ANDROID_EMU_vulkan_null_optional_strings ANDROID_EMU_vulkan_create_resources_with_requirements ANDROID_EMU_YUV_Cache ANDROID_EMU_async_unmap_buffer ANDROID_EMU_vulkan_ignored_handles ANDROID_EMU_has_shared_slots_host_memory_allocator ANDROID_EMU_vulkan_free_memory_sync ANDROID_EMU_vulkan_shader_float16_int8 ANDROID_EMU_vulkan_async_queue_submit ANDROID_EMU_sync_buffer_data GL_OES_vertex_array_object GL_KHR_texture_compression_astc_ldr ANDROID_EMU_host_side_tracing ANDROID_EMU_async_frame_commands ANDROID_EMU_gles_max_version_2
W/OpenGLRenderer: Failed to choose config with EGL_SWAP_BEHAVIOR_PRESERVED, retrying without...
D/EGL_emulation: eglCreateContext: 0xee460760: maj 2 min 0 rcv 2
D/EGL_emulation: eglMakeCurrent: 0xee460760: ver 2 0 (tinfo 0xee7b43f0) (first time)
I/Gralloc4: mapper 4.x is not supported
D/HostConnection: createUnique: call
D/HostConnection: HostConnection::get() New Host Connection established 0xee461330, tid 6768
D/goldfish-address-space: allocate: Ask for block of size 0x100
D/goldfish-address-space: allocate: ioctl allocate returned offset 0x34dffc000 size 0x2000
D/HostConnection: HostComposition ext ANDROID_EMU_CHECKSUM_HELPER_v1 ANDROID_EMU_native_sync_v2 ANDROID_EMU_native_sync_v3 ANDROID_EMU_native_sync_v4 ANDROID_EMU_dma_v1 ANDROID_EMU_direct_mem ANDROID_EMU_host_composition_v1 ANDROID_EMU_host_composition_v2 ANDROID_EMU_vulkan ANDROID_EMU_deferred_vulkan_commands ANDROID_EMU_vulkan_null_optional_strings ANDROID_EMU_vulkan_create_resources_with_requirements ANDROID_EMU_YUV_Cache ANDROID_EMU_async_unmap_buffer ANDROID_EMU_vulkan_ignored_handles ANDROID_EMU_has_shared_slots_host_memory_allocator ANDROID_EMU_vulkan_free_memory_sync ANDROID_EMU_vulkan_shader_float16_int8 ANDROID_EMU_vulkan_async_queue_submit ANDROID_EMU_sync_buffer_data GL_OES_vertex_array_object GL_KHR_texture_compression_astc_ldr ANDROID_EMU_host_side_tracing ANDROID_EMU_async_frame_commands ANDROID_EMU_gles_max_version_2
I/Choreographer: Skipped 45 frames! The application may be doing too much work on its main thread.
I/OpenGLRenderer: Davey! duration=792ms; Flags=0, IntendedVsync=1872865754256, Vsync=1873615754226, OldestInputEvent=9223372036854775807, NewestInputEvent=0, HandleInputStart=1873628675300, AnimationStart=1873628792800, PerformTraversalsStart=1873630847400, DrawStart=1873631928700, SyncQueued=1873632253400, SyncStart=1873637319300, IssueDrawCommandsStart=1873637409900, SwapBuffers=1873651804500, FrameCompleted=1873663434900, DequeueBufferDuration=2445200, QueueBufferDuration=5067700, GpuCompleted=9223372034707292159,
D/CompatibilityChangeReporter: Compat change id reported: 147798919; UID 10121; state: ENABLED
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.ruthvikapplication, PID: 6745
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at com.example.ruthvikapplication.MainActivity.onCreate$lambda-0(MainActivity.kt:21)
at com.example.ruthvikapplication.MainActivity.$r8$lambda$dEE9GmU9yeAvvuQdJ131D5Xmycc(Unknown Source:0)
at com.example.ruthvikapplication.MainActivity$$ExternalSyntheticLambda0.onClick(Unknown Source:6)
at android.view.View.performClick(View.java:7448)
at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1119)
at android.view.View.performClickInternal(View.java:7425)
at android.view.View.access00(View.java:810)
at android.view.View$PerformClick.run(View.java:28305)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
I/Process: Sending signal. PID: 6745 SIG: 9
我认为 XML 中 TextView 的 ID 是 myTitle，这与您在 Kotlin 文件中使用的 ID 不同，即 title
尝试log.d("TextView", title1.toString());
检查确认