当我用导航抽屉单击导航抽屉调用第二个 activity 时，应用程序停止工作
App stops working when I call a second activity with nav drawer from nav drawer click
好的，所以我想让导航抽屉可供所有活动使用。我正在创建一个音板应用程序，当我单击列表中的第 0 项时，我希望它将我带到第一个 activity，其中有一个导航抽屉和第一个音板 activity。从那个 activity 我想打开导航抽屉并单击列表中的另一个项目，它可以带我到 activity 带有音板等等...我有导航抽屉当应用程序打开时工作正常，但当我单击位置 0 将我带到另一个 activity 时，应用程序中的音板关闭，因为它已停止工作。我做错了什么？我将如何纠正它才能工作。
这是我的主要 activity 应用程序启动时打开的代码：
public class MainActivity extends ActionBarActivity {
DrawerLayout mDrawerLayout;
ListView mDrawerList;
ActionBarDrawerToggle mDrawerToggle;
String[] mDrawerListItems;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar)findViewById(R.id.toolbar);
mDrawerLayout = (DrawerLayout)findViewById(R.id.drawer);
mDrawerList = (ListView)findViewById(android.R.id.list);
mDrawerListItems = getResources().getStringArray(R.array.drawer_list);
mDrawerList.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, mDrawerListItems));
mDrawerList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
switch(position) {
case 0:
Intent i = new Intent(MainActivity.this, MrsClubb.class);
startActivity(i);
}
mDrawerLayout.closeDrawer(mDrawerList);
}
});
mDrawerToggle = new ActionBarDrawerToggle(this,
mDrawerLayout,
toolbar,
R.string.drawer_open,
R.string.drawer_close){
public void onDrawerClosed(View v){
super.onDrawerClosed(v);
invalidateOptionsMenu();
syncState();
}
public void onDrawerOpened(View v){
super.onDrawerOpened(v);
invalidateOptionsMenu();
syncState();
}
};
mDrawerLayout.setDrawerListener(mDrawerToggle);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setHomeButtonEnabled(true);
mDrawerToggle.syncState();
}
@Override
protected void onPostCreate(Bundle savedInstanceState){
super.onPostCreate(savedInstanceState);
mDrawerToggle.syncState();
}
@Override
public void onConfigurationChanged(Configuration newConfig){
super.onConfigurationChanged(newConfig);
mDrawerToggle.onConfigurationChanged(newConfig);
}
@Override
public boolean onOptionsItemSelected(MenuItem item){
switch (item.getItemId()){
case android.R.id.home: {
if (mDrawerLayout.isDrawerOpen(mDrawerList)){
mDrawerLayout.closeDrawer(mDrawerList);
} else {
mDrawerLayout.openDrawer(mDrawerList);
}
return true;
}
default: return super.onOptionsItemSelected(item);
}
}
}
这是我的第二个 class，我希望列表视图中的位置 0 将我带到音板中：
public class MrsClubb extends ActionBarActivity {
DrawerLayout mDrawerLayout;
ListView mDrawerList;
ActionBarDrawerToggle mDrawerToggle;
String[] mDrawerListItems;
SoundPool Clubb1;
int clubb1Id;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.mrsclubb);
Clubb1 = new SoundPool(10, AudioManager.STREAM_MUSIC, 1);
clubb1Id = Clubb1.load(this, R.raw.clubb1,1);
Toolbar toolbar = (Toolbar)findViewById(R.id.toolbar);
mDrawerLayout = (DrawerLayout)findViewById(R.id.drawer);
mDrawerList = (ListView)findViewById(android.R.id.list);
mDrawerListItems = getResources().getStringArray(R.array.drawer_list);
mDrawerList.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, mDrawerListItems));
mDrawerList.setOnItemClickListener(new AdapterView.OnItemClickListener()
{
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
switch(position) {
case 0:
Intent i = new Intent(MrsClubb.this, MrsClubb.class);
startActivity(i);
}
mDrawerLayout.closeDrawer(mDrawerList);
}
});
mDrawerToggle = new ActionBarDrawerToggle(this,
mDrawerLayout,
toolbar,
R.string.drawer_open,
R.string.drawer_close){
public void onDrawerClosed(View v){
super.onDrawerClosed(v);
invalidateOptionsMenu();
syncState();
}
public void onDrawerOpened(View v){
super.onDrawerOpened(v);
invalidateOptionsMenu();
syncState();
}
};
mDrawerLayout.setDrawerListener(mDrawerToggle);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setHomeButtonEnabled(true);
mDrawerToggle.syncState();
}
@Override
protected void onPostCreate(Bundle savedInstanceState){
super.onPostCreate(savedInstanceState);
mDrawerToggle.syncState();
}
@Override
public void onConfigurationChanged(Configuration newConfig){
super.onConfigurationChanged(newConfig);
mDrawerToggle.onConfigurationChanged(newConfig);
}
@Override
public boolean onOptionsItemSelected(MenuItem item){
switch (item.getItemId()){
case android.R.id.home: {
if (mDrawerLayout.isDrawerOpen(mDrawerList)){
mDrawerLayout.closeDrawer(mDrawerList);
} else {
mDrawerLayout.openDrawer(mDrawerList);
}
return true;
}
default: return super.onOptionsItemSelected(item);
}
} public void playSound1(View view) {Clubb1.play(clubb1Id, 1, 1, 1, 0, 1);}
}
这是清单：
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".MrsClubb"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MRSCLUBB" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
这里是 LogCat:
-30 21:58:33.984 1971-1971/com.jonatboard.jonat.htssoundboard D/AndroidRuntime﹕ Shutting
down VM
--------- beginning of crash
03-30 21:58:33.985 1971-1971/com.jonatboard.jonat.htssoundboard E/AndroidRuntime﹕
FATAL EXCEPTION: main
Process: com.jonatboard.jonat.htssoundboard, PID: 1971
java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.jonatboard.jonat.htssoundboard/com.jonatboard.jonat.htssoundboard.MrsClu
bb}: java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at com.jonatboard.jonat.htssoundboard.MrsClubb.onCreate(MrsClubb.java:49)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
如果您需要更多代码，请告诉我，非常感谢您的帮助。
这是你的问题：
java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
看起来您的 listView 为 null，请检查以确保您在 activity 中正确声明并找到它。
您的问题是在 MrsClubb activity 中错误地引用了 DrawerLayout 中的 ListView。这是您应该如何使用和引用 ListView 的示例。
<android.support.v4.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent">
<FrameLayout
android:id="@+id/content"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
<ListView
android:id="@+id/drawer"
android:layout_width="240dp"
android:layout_height="match_parent"
android:layout_gravity="start"
android:background="#111"
android:choiceMode="singleChoice"
android:divider="@android:color/transparent"
android:dividerHeight="0dp"/>
</android.support.v4.widget.DrawerLayout>
现在DrawerLayout中的ListView可以引用为：
ListView lv = (ListView) findViewByid(R.id.drawer);
使用 Android 提供的 ID 有时会变得棘手，我相信这就是您出错的地方。
好的，所以我想让导航抽屉可供所有活动使用。我正在创建一个音板应用程序，当我单击列表中的第 0 项时，我希望它将我带到第一个 activity，其中有一个导航抽屉和第一个音板 activity。从那个 activity 我想打开导航抽屉并单击列表中的另一个项目，它可以带我到 activity 带有音板等等...我有导航抽屉当应用程序打开时工作正常，但当我单击位置 0 将我带到另一个 activity 时，应用程序中的音板关闭，因为它已停止工作。我做错了什么？我将如何纠正它才能工作。
这是我的主要 activity 应用程序启动时打开的代码：
public class MainActivity extends ActionBarActivity {
DrawerLayout mDrawerLayout;
ListView mDrawerList;
ActionBarDrawerToggle mDrawerToggle;
String[] mDrawerListItems;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar)findViewById(R.id.toolbar);
mDrawerLayout = (DrawerLayout)findViewById(R.id.drawer);
mDrawerList = (ListView)findViewById(android.R.id.list);
mDrawerListItems = getResources().getStringArray(R.array.drawer_list);
mDrawerList.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, mDrawerListItems));
mDrawerList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
switch(position) {
case 0:
Intent i = new Intent(MainActivity.this, MrsClubb.class);
startActivity(i);
}
mDrawerLayout.closeDrawer(mDrawerList);
}
});
mDrawerToggle = new ActionBarDrawerToggle(this,
mDrawerLayout,
toolbar,
R.string.drawer_open,
R.string.drawer_close){
public void onDrawerClosed(View v){
super.onDrawerClosed(v);
invalidateOptionsMenu();
syncState();
}
public void onDrawerOpened(View v){
super.onDrawerOpened(v);
invalidateOptionsMenu();
syncState();
}
};
mDrawerLayout.setDrawerListener(mDrawerToggle);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setHomeButtonEnabled(true);
mDrawerToggle.syncState();
}
@Override
protected void onPostCreate(Bundle savedInstanceState){
super.onPostCreate(savedInstanceState);
mDrawerToggle.syncState();
}
@Override
public void onConfigurationChanged(Configuration newConfig){
super.onConfigurationChanged(newConfig);
mDrawerToggle.onConfigurationChanged(newConfig);
}
@Override
public boolean onOptionsItemSelected(MenuItem item){
switch (item.getItemId()){
case android.R.id.home: {
if (mDrawerLayout.isDrawerOpen(mDrawerList)){
mDrawerLayout.closeDrawer(mDrawerList);
} else {
mDrawerLayout.openDrawer(mDrawerList);
}
return true;
}
default: return super.onOptionsItemSelected(item);
}
}
}
这是我的第二个 class，我希望列表视图中的位置 0 将我带到音板中：
public class MrsClubb extends ActionBarActivity {
DrawerLayout mDrawerLayout;
ListView mDrawerList;
ActionBarDrawerToggle mDrawerToggle;
String[] mDrawerListItems;
SoundPool Clubb1;
int clubb1Id;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.mrsclubb);
Clubb1 = new SoundPool(10, AudioManager.STREAM_MUSIC, 1);
clubb1Id = Clubb1.load(this, R.raw.clubb1,1);
Toolbar toolbar = (Toolbar)findViewById(R.id.toolbar);
mDrawerLayout = (DrawerLayout)findViewById(R.id.drawer);
mDrawerList = (ListView)findViewById(android.R.id.list);
mDrawerListItems = getResources().getStringArray(R.array.drawer_list);
mDrawerList.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, mDrawerListItems));
mDrawerList.setOnItemClickListener(new AdapterView.OnItemClickListener()
{
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
switch(position) {
case 0:
Intent i = new Intent(MrsClubb.this, MrsClubb.class);
startActivity(i);
}
mDrawerLayout.closeDrawer(mDrawerList);
}
});
mDrawerToggle = new ActionBarDrawerToggle(this,
mDrawerLayout,
toolbar,
R.string.drawer_open,
R.string.drawer_close){
public void onDrawerClosed(View v){
super.onDrawerClosed(v);
invalidateOptionsMenu();
syncState();
}
public void onDrawerOpened(View v){
super.onDrawerOpened(v);
invalidateOptionsMenu();
syncState();
}
};
mDrawerLayout.setDrawerListener(mDrawerToggle);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setHomeButtonEnabled(true);
mDrawerToggle.syncState();
}
@Override
protected void onPostCreate(Bundle savedInstanceState){
super.onPostCreate(savedInstanceState);
mDrawerToggle.syncState();
}
@Override
public void onConfigurationChanged(Configuration newConfig){
super.onConfigurationChanged(newConfig);
mDrawerToggle.onConfigurationChanged(newConfig);
}
@Override
public boolean onOptionsItemSelected(MenuItem item){
switch (item.getItemId()){
case android.R.id.home: {
if (mDrawerLayout.isDrawerOpen(mDrawerList)){
mDrawerLayout.closeDrawer(mDrawerList);
} else {
mDrawerLayout.openDrawer(mDrawerList);
}
return true;
}
default: return super.onOptionsItemSelected(item);
}
} public void playSound1(View view) {Clubb1.play(clubb1Id, 1, 1, 1, 0, 1);}
}
这是清单：
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".MrsClubb"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MRSCLUBB" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
这里是 LogCat:
-30 21:58:33.984 1971-1971/com.jonatboard.jonat.htssoundboard D/AndroidRuntime﹕ Shutting
down VM
--------- beginning of crash
03-30 21:58:33.985 1971-1971/com.jonatboard.jonat.htssoundboard E/AndroidRuntime﹕
FATAL EXCEPTION: main
Process: com.jonatboard.jonat.htssoundboard, PID: 1971
java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.jonatboard.jonat.htssoundboard/com.jonatboard.jonat.htssoundboard.MrsClu
bb}: java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at com.jonatboard.jonat.htssoundboard.MrsClubb.onCreate(MrsClubb.java:49)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
如果您需要更多代码，请告诉我，非常感谢您的帮助。
这是你的问题：
java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
看起来您的 listView 为 null，请检查以确保您在 activity 中正确声明并找到它。
您的问题是在 MrsClubb activity 中错误地引用了 DrawerLayout 中的 ListView。这是您应该如何使用和引用 ListView 的示例。
<android.support.v4.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent">
<FrameLayout
android:id="@+id/content"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
<ListView
android:id="@+id/drawer"
android:layout_width="240dp"
android:layout_height="match_parent"
android:layout_gravity="start"
android:background="#111"
android:choiceMode="singleChoice"
android:divider="@android:color/transparent"
android:dividerHeight="0dp"/>
</android.support.v4.widget.DrawerLayout>
现在DrawerLayout中的ListView可以引用为：
ListView lv = (ListView) findViewByid(R.id.drawer);
使用 Android 提供的 ID 有时会变得棘手，我相信这就是您出错的地方。