尝试在空对象引用上调用虚拟方法 - 抽屉布局
Attempt to invoke virtual method on a null object reference - drawer layout
我正在创建一个扩展 ActionBarActivity 的父级 activity，我的所有活动都将扩展它（因此我只需设置一次抽屉）。
我一直在抽屉列表的 setAdapter 方法上收到空指针异常，但无法弄清楚原因。
这是父级 activity：
（崩溃日志显示这是 activity 的原因，我在该行的末尾添加了注释）
import android.app.Activity;
import android.content.res.Configuration;
import android.graphics.Color;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBar;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.RelativeLayout;
import android.widget.TextView;
import com.makeramen.RoundedImageView;
import com.makeramen.RoundedTransformationBuilder;
import com.squareup.picasso.Picasso;
import com.squareup.picasso.Transformation;
public class MainActivity extends ActionBarActivity implements AdapterView.OnItemClickListener {
// Action bar
private ActionBar actionBar;
private Toolbar toolbar;
// Navigation Drawer
private ActionBarDrawerToggle drawerToggle;
private DrawerLayout drawerLayout;
private ListView drawerList;
private RelativeLayout drawerHeader;
private ImageView drawerHeaderBG;
private RoundedImageView userImage;
private TextView userName;
public void setupActivity() {
setMyActionBar();
createDrawer();
}
public void setMyActionBar() {
toolbar = (Toolbar) findViewById(R.id.toolbar);
toolbar.setTitleTextColor(Color.WHITE);
setSupportActionBar(toolbar);
actionBar = getSupportActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);
actionBar.setHomeButtonEnabled(true);
actionBar.setTitle(getString(R.string.app_name));
actionBar.setDisplayShowTitleEnabled(true);
actionBar.setDisplayHomeAsUpEnabled(getSupportFragmentManager().getBackStackEntryCount() > 0);
}
public void createDrawer() {
drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
drawerLayout.post(new Runnable() {
@Override
public void run() {
drawerList = (ListView) drawerLayout.findViewById(R.id.left_drawer);
drawerList.setMinimumWidth(((View) findViewById(R.id.baseLayoutRootParent)).getWidth() - actionBar.getHeight());
if (drawerList.getHeaderViewsCount() == 0)
drawerList.addHeaderView(drawerHeader);
drawerList.setAdapter(new DrawerAdapter(MainActivity.this)); // crash happens here
drawerList.setOnItemClickListener(MainActivity.this);
drawerToggle = new ActionBarDrawerToggle(
MainActivity.this, /* host Activity */
drawerLayout, /* DrawerLayout object */
R.drawable.ic_action_navigation_menu, /* nav drawer icon to replace 'Up' caret */
R.string.open_drawer, /* "open drawer" description */
R.string.close_drawer /* "close drawer" description */
) {
/**
* Called when a drawer has settled in a completely closed state.
*/
public void onDrawerClosed(View view) {
actionBar.setTitle(getString(R.string.app_name));
}
/**
* Called when a drawer has settled in a completely open state.
*/
public void onDrawerOpened(View drawerView) {
actionBar.setTitle(getString(R.string.app_name));
}
};
// Set the drawer toggle as the DrawerListener
drawerLayout.setDrawerListener(drawerToggle);
drawerToggle.syncState();
}
});
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
// drawer list item click events
}
@Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
drawerToggle.onConfigurationChanged(newConfig);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
if (drawerToggle.onOptionsItemSelected(item)) {
return true;
}
switch (item.getItemId()) {
case R.id.action_settings:
return true;
}
return super.onOptionsItemSelected(item);
}
}
这是扩展前一个的 activity：
public class HomeActivity extends MainActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_layout);
setupActivity();
getSupportFragmentManager().beginTransaction().replace(R.id.mainContainer, MainFragment.newInstance()).commit();
}
}
这是抽屉列表的适配器：
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;
public class DrawerAdapter extends BaseAdapter {
private Context context;
private String[] items;
public DrawerAdapter(Context context) {
this.context = context;
items = context.getResources().getStringArray(R.array.drawer_array);
}
@Override
public int getCount() {
return items.length;
}
@Override
public String getItem(int position) {
return items[position];
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
holder = new ViewHolder();
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(R.layout.drawer_list_item, parent, false);
holder.image = (ImageView) convertView.findViewById(R.id.drawerItemImage);
holder.text = (TextView) convertView.findViewById(R.id.drawerItemText);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
holder.image.setImageResource(getIcon(position));
holder.text.setText(getItem(position));
return convertView;
}
private int getIcon(int position) {
switch (position) {
case 0:
return R.drawable.ic_action_home_blue;
case 1:
return R.drawable.ic_action_heart_blue;
case 2:
return R.drawable.ic_action_search_blue;
case 3:
return R.drawable.ic_action_map_blue;
case 4:
return R.drawable.ic_action_wheel_blue;
case 5:
return R.drawable.ic_action_calendar_blue;
case 6:
return R.drawable.ic_action_parameters_blue;
}
return 0;
}
class ViewHolder {
private ImageView image;
private TextView text;
}
}
为了以防万一，这里是布局文件：
<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"
android:background="?attr/color">
<!-- The main content view -->
<LinearLayout
android:id="@+id/baseLayoutRootParent"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.v7.widget.Toolbar xmlns:bar="http://schemas.android.com/apk/res-auto"
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
android:gravity="end|center_vertical"
android:paddingEnd="@dimen/activity_horizontal_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingStart="@dimen/activity_horizontal_margin"
bar:theme="@style/ThemeOverlay.AppCompat.ActionBar" />
<FrameLayout
android:id="@+id/mainContainer"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
<!-- The drawer content view -->
<ListView
android:id="@+id/left_drawer"
android:layout_width="250dp"
android:layout_height="match_parent"
android:layout_gravity="start"
android:background="?attr/background"
android:choiceMode="singleChoice"
android:divider="@android:color/transparent"
android:dividerHeight="0dp" />
</android.support.v4.widget.DrawerLayout>
最后，这是错误日志：
02-27 13:05:55.205 11723-11723/com.example.myApp.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.myApp.app, PID: 11723
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.ViewGroup$LayoutParams android.view.View.getLayoutParams()' on a null object reference
at android.widget.ListView.clearRecycledState(ListView.java:539)
at android.widget.ListView.resetList(ListView.java:525)
at android.widget.ListView.setAdapter(ListView.java:469)
at com.example.myApp.app.MainActivity.run(MainActivity.java:92)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:155)
at android.app.ActivityThread.main(ActivityThread.java:5696)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1028)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:823)
提前致谢！
编辑
我试过从 onCreate、onPostCreate 和 onResume 调用 setupActivity() 并在所有 3 个中都得到相同的错误
所以，我也遇到了这个奇怪的错误，但我的错误日志没有指向我的应用程序中的任何代码行，所以这是一个关于问题出在哪里的猜谜游戏。
它是：
listView.scrollToPosition(0);
Cursor results = performQuery();
if(results != null){
adapter.changeCursor(results);
}
我的崩溃是在没有结果的情况下发生的，所以我最终决定使用空视图。
Cursor results = performQuery();
if(results != null && results.getCount() > 0){
listView.setVisibility(View.VISIBLE);
emptyView.setVisibility(View.GONE);
adapter.changeCursor(results);
listView.scrollToPosition(0);
}
else{
emptyView.setVisibility(View.VISIBLE);
listView.setVisibility(View.GONE);
}
这解决了我的崩溃问题。请注意，我使用的是新的 RecyclerView.
我正在创建一个扩展 ActionBarActivity 的父级 activity，我的所有活动都将扩展它（因此我只需设置一次抽屉）。
我一直在抽屉列表的 setAdapter 方法上收到空指针异常，但无法弄清楚原因。
这是父级 activity： （崩溃日志显示这是 activity 的原因，我在该行的末尾添加了注释）
import android.app.Activity;
import android.content.res.Configuration;
import android.graphics.Color;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBar;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.RelativeLayout;
import android.widget.TextView;
import com.makeramen.RoundedImageView;
import com.makeramen.RoundedTransformationBuilder;
import com.squareup.picasso.Picasso;
import com.squareup.picasso.Transformation;
public class MainActivity extends ActionBarActivity implements AdapterView.OnItemClickListener {
// Action bar
private ActionBar actionBar;
private Toolbar toolbar;
// Navigation Drawer
private ActionBarDrawerToggle drawerToggle;
private DrawerLayout drawerLayout;
private ListView drawerList;
private RelativeLayout drawerHeader;
private ImageView drawerHeaderBG;
private RoundedImageView userImage;
private TextView userName;
public void setupActivity() {
setMyActionBar();
createDrawer();
}
public void setMyActionBar() {
toolbar = (Toolbar) findViewById(R.id.toolbar);
toolbar.setTitleTextColor(Color.WHITE);
setSupportActionBar(toolbar);
actionBar = getSupportActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);
actionBar.setHomeButtonEnabled(true);
actionBar.setTitle(getString(R.string.app_name));
actionBar.setDisplayShowTitleEnabled(true);
actionBar.setDisplayHomeAsUpEnabled(getSupportFragmentManager().getBackStackEntryCount() > 0);
}
public void createDrawer() {
drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
drawerLayout.post(new Runnable() {
@Override
public void run() {
drawerList = (ListView) drawerLayout.findViewById(R.id.left_drawer);
drawerList.setMinimumWidth(((View) findViewById(R.id.baseLayoutRootParent)).getWidth() - actionBar.getHeight());
if (drawerList.getHeaderViewsCount() == 0)
drawerList.addHeaderView(drawerHeader);
drawerList.setAdapter(new DrawerAdapter(MainActivity.this)); // crash happens here
drawerList.setOnItemClickListener(MainActivity.this);
drawerToggle = new ActionBarDrawerToggle(
MainActivity.this, /* host Activity */
drawerLayout, /* DrawerLayout object */
R.drawable.ic_action_navigation_menu, /* nav drawer icon to replace 'Up' caret */
R.string.open_drawer, /* "open drawer" description */
R.string.close_drawer /* "close drawer" description */
) {
/**
* Called when a drawer has settled in a completely closed state.
*/
public void onDrawerClosed(View view) {
actionBar.setTitle(getString(R.string.app_name));
}
/**
* Called when a drawer has settled in a completely open state.
*/
public void onDrawerOpened(View drawerView) {
actionBar.setTitle(getString(R.string.app_name));
}
};
// Set the drawer toggle as the DrawerListener
drawerLayout.setDrawerListener(drawerToggle);
drawerToggle.syncState();
}
});
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
// drawer list item click events
}
@Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
drawerToggle.onConfigurationChanged(newConfig);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
if (drawerToggle.onOptionsItemSelected(item)) {
return true;
}
switch (item.getItemId()) {
case R.id.action_settings:
return true;
}
return super.onOptionsItemSelected(item);
}
}
这是扩展前一个的 activity：
public class HomeActivity extends MainActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_layout);
setupActivity();
getSupportFragmentManager().beginTransaction().replace(R.id.mainContainer, MainFragment.newInstance()).commit();
}
}
这是抽屉列表的适配器：
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;
public class DrawerAdapter extends BaseAdapter {
private Context context;
private String[] items;
public DrawerAdapter(Context context) {
this.context = context;
items = context.getResources().getStringArray(R.array.drawer_array);
}
@Override
public int getCount() {
return items.length;
}
@Override
public String getItem(int position) {
return items[position];
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
holder = new ViewHolder();
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(R.layout.drawer_list_item, parent, false);
holder.image = (ImageView) convertView.findViewById(R.id.drawerItemImage);
holder.text = (TextView) convertView.findViewById(R.id.drawerItemText);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
holder.image.setImageResource(getIcon(position));
holder.text.setText(getItem(position));
return convertView;
}
private int getIcon(int position) {
switch (position) {
case 0:
return R.drawable.ic_action_home_blue;
case 1:
return R.drawable.ic_action_heart_blue;
case 2:
return R.drawable.ic_action_search_blue;
case 3:
return R.drawable.ic_action_map_blue;
case 4:
return R.drawable.ic_action_wheel_blue;
case 5:
return R.drawable.ic_action_calendar_blue;
case 6:
return R.drawable.ic_action_parameters_blue;
}
return 0;
}
class ViewHolder {
private ImageView image;
private TextView text;
}
}
为了以防万一，这里是布局文件：
<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"
android:background="?attr/color">
<!-- The main content view -->
<LinearLayout
android:id="@+id/baseLayoutRootParent"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.v7.widget.Toolbar xmlns:bar="http://schemas.android.com/apk/res-auto"
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
android:gravity="end|center_vertical"
android:paddingEnd="@dimen/activity_horizontal_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingStart="@dimen/activity_horizontal_margin"
bar:theme="@style/ThemeOverlay.AppCompat.ActionBar" />
<FrameLayout
android:id="@+id/mainContainer"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
<!-- The drawer content view -->
<ListView
android:id="@+id/left_drawer"
android:layout_width="250dp"
android:layout_height="match_parent"
android:layout_gravity="start"
android:background="?attr/background"
android:choiceMode="singleChoice"
android:divider="@android:color/transparent"
android:dividerHeight="0dp" />
</android.support.v4.widget.DrawerLayout>
最后，这是错误日志：
02-27 13:05:55.205 11723-11723/com.example.myApp.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.myApp.app, PID: 11723
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.ViewGroup$LayoutParams android.view.View.getLayoutParams()' on a null object reference
at android.widget.ListView.clearRecycledState(ListView.java:539)
at android.widget.ListView.resetList(ListView.java:525)
at android.widget.ListView.setAdapter(ListView.java:469)
at com.example.myApp.app.MainActivity.run(MainActivity.java:92)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:155)
at android.app.ActivityThread.main(ActivityThread.java:5696)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1028)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:823)
提前致谢！
编辑
我试过从 onCreate、onPostCreate 和 onResume 调用 setupActivity() 并在所有 3 个中都得到相同的错误
所以，我也遇到了这个奇怪的错误，但我的错误日志没有指向我的应用程序中的任何代码行，所以这是一个关于问题出在哪里的猜谜游戏。 它是：
listView.scrollToPosition(0);
Cursor results = performQuery();
if(results != null){
adapter.changeCursor(results);
}
我的崩溃是在没有结果的情况下发生的，所以我最终决定使用空视图。
Cursor results = performQuery();
if(results != null && results.getCount() > 0){
listView.setVisibility(View.VISIBLE);
emptyView.setVisibility(View.GONE);
adapter.changeCursor(results);
listView.scrollToPosition(0);
}
else{
emptyView.setVisibility(View.VISIBLE);
listView.setVisibility(View.GONE);
}
这解决了我的崩溃问题。请注意，我使用的是新的 RecyclerView.