java.lang.NullPointerException 与 parent.getChildAt(位置) GridView
java.lang.NullPointerException with parent.getChildAt(position) GridView
当我尝试管理我的 GridView 的项目时遇到一些问题，当位置 if >= 6 时。位置 1,2,3,4,5 一切正常。
这是我的名册 class:
public class MyRoster extends ActionBarActivity implements AdapterView.OnItemClickListener {
GridView cardsGridView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my_roster);
cardsGridView = (GridView) findViewById(R.id.cardsGridView);
cardsGridView.setAdapter(new MyAdapter(this));
cardsGridView.setOnItemClickListener(this);
}
@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_my_roster, 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.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Log.d("MYTAG", "DENTRO ON ITEMCLICK");
switch(parent.getId()){
case R.id.cardsGridView:
ImageView prova = (ImageView)parent.getChildAt(position+1);
// ImageView prova = (ImageView)parent.getItemAtPosition(position+1);
prova.setImageResource(R.drawable.checked_checkbox);
break;
}
}
}
这是用于管理 GridView 项目的 class 适配器：
public class MyAdapter extends BaseAdapter{
private List<Item> items = new ArrayList<Item>();
private LayoutInflater inflater;
Integer[] myCardsInteger = takeMyCardsFromDB(); // return an int array
public MyAdapter(Context context) {
inflater = LayoutInflater.from(context);
for( int i = 0; i < myCardsInteger.length; i++){
String key = "" + i;
items.add(new Item(key, myCardsInteger[i] ));
items.add(new Item(key, R.drawable.unchecked_checkbox));
}
}
// da implementare!!
private Integer[] takeMyCardsFromDB(){
// prendo le carte che possiede l'utente dal database interno
Integer[] prova = {R.drawable.two, R.drawable.one, R.drawable.three, R.drawable.four,R.drawable.five,R.drawable.ahah,R.drawable.foeuehu};
return prova;
}
@Override
public int getCount() {
return items.size();
}
@Override
public Object getItem(int i) {
return items.get(i);
}
@Override
public long getItemId(int i) {
return items.get(i).drawableId;
}
@Override
public View getView(int i, View view, ViewGroup viewGroup) {
View v = view;
ImageView picture;
TextView name;
if(v == null) {
v = inflater.inflate(R.layout.row_my_roster_card, viewGroup, false);
v.setTag(R.id.picture, v.findViewById(R.id.picture));
}
picture = (ImageView)v.getTag(R.id.picture);
Item item = (Item)getItem(i);
picture.setImageResource(item.drawableId);
return v;
}
private class Item {
final String name;
final int drawableId;
Item(String name, int drawableId) {
this.name = name;
this.drawableId = drawableId;
}
}
}
GridView单项为ImageView。
布局代码：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context="com.oldmount.fba.MyRoster">
<LinearLayout
android:id="@+id/prova"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<TextView
android:text="SELEZIONA LA TUA ROSA!"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal"
android:layout_below="@id/prova">
<GridView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/cardsGridView"
android:numColumns="2"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</LinearLayout>
当我点击一个项目时，我想在下一个位置更改该项目。
在我的适配器 class 中，我实例化了超过 12 个项目，
但是当我点击项目编号 6 和后续项目时，我有一个 nullpointerexception。
logcat:
29 19:22:38.867 2420-2420/-------E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: --------, PID: 2420
java.lang.NullPointerException
at -----.MyRoster.onItemClick(MyRoster.java:82)
at android.widget.AdapterView.performItemClick(AdapterView.java:308)
at android.widget.AbsListView.performItemClick(AbsListView.java:1510)
at android.widget.AbsListView$PerformClick.run(AbsListView.java:3472)
at android.widget.AbsListView.run(AbsListView.java:4835)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:146)
at android.app.ActivityThread.main(ActivityThread.java:5593)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
at dalvik.system.NativeStart.main(Native Method)
这个错误让我失去了理智。有人能帮我吗？
我认为这段代码是你的问题。
ImageView prova = (ImageView)parent.getChildAt(position+1);
在您的 MyAdapter class 中添加此方法：
public void setView(int position ){
String key = ""+ position;
items.remove(position);
items.add(position , new Item(key, R.drawable.checked_checkbox));
}
在您的 MyRoster class 中实例化一个 MyAdapter 对象并在您的 OnItemClick 中使用此代码：
myAdapter.setView(position);
您总是直接在适配器中更改项目class以保留更改。
当我尝试管理我的 GridView 的项目时遇到一些问题，当位置 if >= 6 时。位置 1,2,3,4,5 一切正常。 这是我的名册 class:
public class MyRoster extends ActionBarActivity implements AdapterView.OnItemClickListener {
GridView cardsGridView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my_roster);
cardsGridView = (GridView) findViewById(R.id.cardsGridView);
cardsGridView.setAdapter(new MyAdapter(this));
cardsGridView.setOnItemClickListener(this);
}
@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_my_roster, 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.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Log.d("MYTAG", "DENTRO ON ITEMCLICK");
switch(parent.getId()){
case R.id.cardsGridView:
ImageView prova = (ImageView)parent.getChildAt(position+1);
// ImageView prova = (ImageView)parent.getItemAtPosition(position+1);
prova.setImageResource(R.drawable.checked_checkbox);
break;
}
}
}
这是用于管理 GridView 项目的 class 适配器：
public class MyAdapter extends BaseAdapter{
private List<Item> items = new ArrayList<Item>();
private LayoutInflater inflater;
Integer[] myCardsInteger = takeMyCardsFromDB(); // return an int array
public MyAdapter(Context context) {
inflater = LayoutInflater.from(context);
for( int i = 0; i < myCardsInteger.length; i++){
String key = "" + i;
items.add(new Item(key, myCardsInteger[i] ));
items.add(new Item(key, R.drawable.unchecked_checkbox));
}
}
// da implementare!!
private Integer[] takeMyCardsFromDB(){
// prendo le carte che possiede l'utente dal database interno
Integer[] prova = {R.drawable.two, R.drawable.one, R.drawable.three, R.drawable.four,R.drawable.five,R.drawable.ahah,R.drawable.foeuehu};
return prova;
}
@Override
public int getCount() {
return items.size();
}
@Override
public Object getItem(int i) {
return items.get(i);
}
@Override
public long getItemId(int i) {
return items.get(i).drawableId;
}
@Override
public View getView(int i, View view, ViewGroup viewGroup) {
View v = view;
ImageView picture;
TextView name;
if(v == null) {
v = inflater.inflate(R.layout.row_my_roster_card, viewGroup, false);
v.setTag(R.id.picture, v.findViewById(R.id.picture));
}
picture = (ImageView)v.getTag(R.id.picture);
Item item = (Item)getItem(i);
picture.setImageResource(item.drawableId);
return v;
}
private class Item {
final String name;
final int drawableId;
Item(String name, int drawableId) {
this.name = name;
this.drawableId = drawableId;
}
}
}
GridView单项为ImageView。 布局代码：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context="com.oldmount.fba.MyRoster">
<LinearLayout
android:id="@+id/prova"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<TextView
android:text="SELEZIONA LA TUA ROSA!"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal"
android:layout_below="@id/prova">
<GridView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/cardsGridView"
android:numColumns="2"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</LinearLayout>
当我点击一个项目时，我想在下一个位置更改该项目。 在我的适配器 class 中，我实例化了超过 12 个项目， 但是当我点击项目编号 6 和后续项目时，我有一个 nullpointerexception。
logcat:
29 19:22:38.867 2420-2420/-------E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: --------, PID: 2420
java.lang.NullPointerException
at -----.MyRoster.onItemClick(MyRoster.java:82)
at android.widget.AdapterView.performItemClick(AdapterView.java:308)
at android.widget.AbsListView.performItemClick(AbsListView.java:1510)
at android.widget.AbsListView$PerformClick.run(AbsListView.java:3472)
at android.widget.AbsListView.run(AbsListView.java:4835)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:146)
at android.app.ActivityThread.main(ActivityThread.java:5593)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
at dalvik.system.NativeStart.main(Native Method)
这个错误让我失去了理智。有人能帮我吗？
我认为这段代码是你的问题。
ImageView prova = (ImageView)parent.getChildAt(position+1);
在您的 MyAdapter class 中添加此方法：
public void setView(int position ){
String key = ""+ position;
items.remove(position);
items.add(position , new Item(key, R.drawable.checked_checkbox));
}
在您的 MyRoster class 中实例化一个 MyAdapter 对象并在您的 OnItemClick 中使用此代码：
myAdapter.setView(position);
您总是直接在适配器中更改项目class以保留更改。