当我将 onClickListener 放在 ImageView 上时，它使我的应用程序崩溃
It crashes my app when I put onClickListener on a ImageView
总结问题
开发者您好，
所以.. 我正在寻找一个 PopupMenù，它会在单击以下图标时出现，该图标停留在 ListView 中的项目上。我想在点击时出现带有一些选项的弹出栏
描述您尝试过的内容
我尝试按照有关创建 Popup Menù 的教程进行操作，但方法始终相同，我对此没有任何问题。但它向我显示 Logcat 上的空指针错误，我尝试通过初始化 ImageView 来修复，但目前没有任何正确的方法。
我尝试做一些类似“image = (Imageview)findviewbyId(R.id.imagesrc)”的事情，但它总是出现以下错误：
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.isilente/com.example.isilente.HomePage}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
在适当的时候，显示一些代码
我在编码时遇到这种情况：
Class -> Homepage.java
public class HomePage extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {
DrawerLayout drawerLayout;
NavigationView navigationView;
Toolbar toolbar;
private AppCompatButton getstart, augurio;
//new stuff
private ArrayList<Music> my_mainarraylist;
private MusicAdapter my_musicadapter;
private ListView listView_songs;
ImageView imageView_puntini;
//end new stuff
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home_page);
getstart=findViewById(R.id.GetStart);
imageView_puntini=findViewById(R.id.imageview_puntini);
listView_songs=findViewById(R.id.listview_buongiorno);
//START NEW STUFF
my_mainarraylist=new ArrayList<>();
my_mainarraylist.add(new Music("Buongiorno#1", "Pozione Polisucchio", R.raw.silente, R.id.imageview_play, R.id.imageview_stop, R.id.imageview_puntini));
my_mainarraylist.add(new Music("Augurio", "Hai dato il massimo", R.raw.massimo, R.id.imageview_play, R.id.imageview_stop, R.id.imageview_puntini));
MusicAdapter adapter = new MusicAdapter(this, R.layout.songs_item_listview,my_mainarraylist);
listView_songs.setAdapter(adapter);
listView_songs.setVisibility(View.GONE);
//FINE NEW STUFF
/*----Hooks----*/
drawerLayout = findViewById(R.id.drawerLayout);
navigationView = findViewById(R.id.nav_view);
toolbar = findViewById(R.id.toolbar);
/*----Toolbar----*/
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayShowTitleEnabled(false);
/*----NavigationDrawerMenu----*/
//Menu menu = navigationView.getMenu();
navigationView.bringToFront();
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawerLayout, toolbar,R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawerLayout.addDrawerListener(toggle);
toggle.syncState();
//navigationView.setCheckedItem(R.id.nav_home);
navigationView.setNavigationItemSelectedListener(this);
getstart.setOnClickListener(v -> listView_songs.setVisibility(View.VISIBLE));
//popup
imageView_puntini.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
PopupMenu popupMenu = new PopupMenu(HomePage.this, v);
MenuInflater menuInflater = popupMenu.getMenuInflater();
menuInflater.inflate(R.menu.menuset, popupMenu.getMenu());
popupMenu.show();
}
});
//popup end
}
在 res/menu 中：
<menu><item
android:id="@+id/item_settings"
android:title="Settings"
android:showAsAction="ifRoom|withText"
/>
<item
android:id="@+id/item_about"
android:title="About"
android:showAsAction="ifRoom|withText"
/></menu>
然后我得到了这个，它是 ListView 上的项目.. songs-item-listview.xml:
<?xml version="1.0" encoding="utf-8"?>
<androidx.appcompat.widget.LinearLayoutCompat xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingTop="5dp"
android:paddingBottom="5dp"
android:background="#152238"
android:paddingLeft="5dp"
android:paddingRight="16dp">
<ImageView
android:id="@+id/audio_microfono"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/ic__431742_audio_communication_instrument_media_microphone_icon"
/>
<androidx.appcompat.widget.LinearLayoutCompat
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="3"
android:orientation="vertical">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/textview_songs"
android:text="Current song"
android:textStyle="bold"
android:textColor="#eee86b"
android:textSize="16sp"
android:layout_toEndOf="@+id/audio_microfono"
/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/textview_artist"
android:text="Current artist"
android:textStyle="italic"
android:textColor="#eee86b"
android:layout_toEndOf="@+id/audio_microfono"
android:layout_below="@+id/textview_songs"
android:textSize="16sp"
/>
</androidx.appcompat.widget.LinearLayoutCompat>
<androidx.appcompat.widget.LinearLayoutCompat
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="5dp"
android:orientation="horizontal">
<ImageView
android:id="@+id/imageview_play"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:paddingRight="10dp"
android:src="@drawable/ic_play"/>
<ImageView
android:id="@+id/imageview_stop"
android:layout_width="wrap_content"
android:layout_alignParentEnd="true"
android:paddingRight="5dp"
android:layout_height="wrap_content"
android:src="@drawable/ic_stop"
/>
<ImageView
android:id="@+id/imageview_puntini"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/ic_trepuntini"
/>
</androidx.appcompat.widget.LinearLayoutCompat>
</androidx.appcompat.widget.LinearLayoutCompat>
有人说按钮不在主按钮中可能是错误 activity 但它在另一个主按钮中，但无论如何，你建议我做什么？
Ps: 这是 LogCat :
2021-09-05 20:20:19.629 9883-9883/com.example.isilente
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.isilente, PID: 9883
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.isilente/com.example.isilente.HomePage}:
java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.ImageView.setOnClickListener(android.view.View$OnClickListener)'
on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3449)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.ImageView.setOnClickListener(android.view.View$OnClickListener)'
on a null object reference
at com.example.isilente.HomePage.onCreate(HomePage.java:94)
at android.app.Activity.performCreate(Activity.java:8000)
at android.app.Activity.performCreate(Activity.java:7984)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3422)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
at android.os.Handler.dispatchMessage(Handler.java:106)
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$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
Blockquote
Blockquote
Blockquote
请添加这个
<ImageView
android:id="@+id/imageview_puntini"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/ic_trepuntini"
/>
到 activity_home_page.xml 您定义了列表视图而不是列表视图项 songs-item-listview.xml，因为您正试图从 activity.
访问它
尝试像这样初始化你的 PopupMenu
popup.getMenu().add(groupId, itemId, order, title);
对于您要添加的每个 MenuItem。
您还可以查看此 link 以查看其他解决方案
（我的解决方案来自 this man）
总结问题
开发者您好，
所以.. 我正在寻找一个 PopupMenù，它会在单击以下图标时出现，该图标停留在 ListView 中的项目上。我想在点击时出现带有一些选项的弹出栏
描述您尝试过的内容
我尝试按照有关创建 Popup Menù 的教程进行操作，但方法始终相同，我对此没有任何问题。但它向我显示 Logcat 上的空指针错误，我尝试通过初始化 ImageView 来修复，但目前没有任何正确的方法。
我尝试做一些类似“image = (Imageview)findviewbyId(R.id.imagesrc)”的事情，但它总是出现以下错误：
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.isilente/com.example.isilente.HomePage}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
在适当的时候，显示一些代码
我在编码时遇到这种情况：
Class -> Homepage.java
public class HomePage extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {
DrawerLayout drawerLayout;
NavigationView navigationView;
Toolbar toolbar;
private AppCompatButton getstart, augurio;
//new stuff
private ArrayList<Music> my_mainarraylist;
private MusicAdapter my_musicadapter;
private ListView listView_songs;
ImageView imageView_puntini;
//end new stuff
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home_page);
getstart=findViewById(R.id.GetStart);
imageView_puntini=findViewById(R.id.imageview_puntini);
listView_songs=findViewById(R.id.listview_buongiorno);
//START NEW STUFF
my_mainarraylist=new ArrayList<>();
my_mainarraylist.add(new Music("Buongiorno#1", "Pozione Polisucchio", R.raw.silente, R.id.imageview_play, R.id.imageview_stop, R.id.imageview_puntini));
my_mainarraylist.add(new Music("Augurio", "Hai dato il massimo", R.raw.massimo, R.id.imageview_play, R.id.imageview_stop, R.id.imageview_puntini));
MusicAdapter adapter = new MusicAdapter(this, R.layout.songs_item_listview,my_mainarraylist);
listView_songs.setAdapter(adapter);
listView_songs.setVisibility(View.GONE);
//FINE NEW STUFF
/*----Hooks----*/
drawerLayout = findViewById(R.id.drawerLayout);
navigationView = findViewById(R.id.nav_view);
toolbar = findViewById(R.id.toolbar);
/*----Toolbar----*/
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayShowTitleEnabled(false);
/*----NavigationDrawerMenu----*/
//Menu menu = navigationView.getMenu();
navigationView.bringToFront();
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawerLayout, toolbar,R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawerLayout.addDrawerListener(toggle);
toggle.syncState();
//navigationView.setCheckedItem(R.id.nav_home);
navigationView.setNavigationItemSelectedListener(this);
getstart.setOnClickListener(v -> listView_songs.setVisibility(View.VISIBLE));
//popup
imageView_puntini.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
PopupMenu popupMenu = new PopupMenu(HomePage.this, v);
MenuInflater menuInflater = popupMenu.getMenuInflater();
menuInflater.inflate(R.menu.menuset, popupMenu.getMenu());
popupMenu.show();
}
});
//popup end
}
在 res/menu 中：
<menu><item
android:id="@+id/item_settings"
android:title="Settings"
android:showAsAction="ifRoom|withText"
/>
<item
android:id="@+id/item_about"
android:title="About"
android:showAsAction="ifRoom|withText"
/></menu>
然后我得到了这个，它是 ListView 上的项目.. songs-item-listview.xml:
<?xml version="1.0" encoding="utf-8"?>
<androidx.appcompat.widget.LinearLayoutCompat xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingTop="5dp"
android:paddingBottom="5dp"
android:background="#152238"
android:paddingLeft="5dp"
android:paddingRight="16dp">
<ImageView
android:id="@+id/audio_microfono"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/ic__431742_audio_communication_instrument_media_microphone_icon"
/>
<androidx.appcompat.widget.LinearLayoutCompat
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="3"
android:orientation="vertical">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/textview_songs"
android:text="Current song"
android:textStyle="bold"
android:textColor="#eee86b"
android:textSize="16sp"
android:layout_toEndOf="@+id/audio_microfono"
/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/textview_artist"
android:text="Current artist"
android:textStyle="italic"
android:textColor="#eee86b"
android:layout_toEndOf="@+id/audio_microfono"
android:layout_below="@+id/textview_songs"
android:textSize="16sp"
/>
</androidx.appcompat.widget.LinearLayoutCompat>
<androidx.appcompat.widget.LinearLayoutCompat
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="5dp"
android:orientation="horizontal">
<ImageView
android:id="@+id/imageview_play"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:paddingRight="10dp"
android:src="@drawable/ic_play"/>
<ImageView
android:id="@+id/imageview_stop"
android:layout_width="wrap_content"
android:layout_alignParentEnd="true"
android:paddingRight="5dp"
android:layout_height="wrap_content"
android:src="@drawable/ic_stop"
/>
<ImageView
android:id="@+id/imageview_puntini"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/ic_trepuntini"
/>
</androidx.appcompat.widget.LinearLayoutCompat>
</androidx.appcompat.widget.LinearLayoutCompat>
有人说按钮不在主按钮中可能是错误 activity 但它在另一个主按钮中，但无论如何，你建议我做什么？
Ps: 这是 LogCat :
2021-09-05 20:20:19.629 9883-9883/com.example.isilente E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.isilente, PID: 9883 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.isilente/com.example.isilente.HomePage}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3449) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066) at android.os.Handler.dispatchMessage(Handler.java:106) 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$MethodAndArgsCaller.run(RuntimeInit.java:592) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at com.example.isilente.HomePage.onCreate(HomePage.java:94) at android.app.Activity.performCreate(Activity.java:8000) at android.app.Activity.performCreate(Activity.java:7984) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3422) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:223) at android.app.ActivityThread.main(ActivityThread.java:7656) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
Blockquote Blockquote Blockquote
请添加这个
<ImageView
android:id="@+id/imageview_puntini"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/ic_trepuntini"
/>
到 activity_home_page.xml 您定义了列表视图而不是列表视图项 songs-item-listview.xml，因为您正试图从 activity.
尝试像这样初始化你的 PopupMenu
popup.getMenu().add(groupId, itemId, order, title);
对于您要添加的每个 MenuItem。
您还可以查看此 link 以查看其他解决方案
（我的解决方案来自 this man）