我的应用程序继续停止，我不知道为什么。它是片段中的绘图应用程序，允许用户绘制。我是初学程序员，所以任何帮助都会非常感谢你！
Field Fragment：
package com.example.marlon.fieldapp;
import android.app.DialogFragment;
import android.content.Context;
import android.graphics.Color;
import android.media.Image;
import android.net.Uri;
import android.os.Bundle;
import android.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageButton;
import android.widget.LinearLayout;
import java.util.UUID;
import android.provider.MediaStore;
import android.app.AlertDialog;
import android.app.Dialog;
import android.content.DialogInterface;
import android.view.View.OnClickListener;
import android.widget.Toast;
/**
* A simple {@link Fragment} subclass.
* Activities that contain this fragment must implement the
* {@link Field_fragment.OnFragmentInteractionListener} interface
* to handle interaction events.
* Use the {@link Field_fragment#newInstance} factory method to
* create an instance of this fragment.
*/
public class Field_fragment extends Fragment implements OnClickListener
{
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
private DrawingView drawView;
private ImageButton currPaint, drawBtn;
private float smallBrush, mediumBrush, largeBrush;
private OnFragmentInteractionListener mListener;
public Field_fragment() {
// Required empty public constructor
}
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @param param2 Parameter 2.
* @return A new instance of fragment Field_fragment.
*/
// TODO: Rename and change types and number of parameters
public static Field_fragment newInstance(String param1, String param2)
{
Field_fragment fragment = new Field_fragment();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState)
{
smallBrush = getResources().getInteger(R.integer.small_size);
mediumBrush = getResources().getInteger(R.integer.medium_size);
largeBrush = getResources().getInteger(R.integer.large_size);
drawBtn = (ImageButton)getView().findViewById(R.id.draw_btn);
drawBtn.setOnClickListener(this);
drawView.setBrushSize(mediumBrush);
super.onCreate(savedInstanceState);
if (getArguments() != null)
{
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
{
// Inflate the layout for this fragment
drawView = (DrawingView) drawView.findViewById(R.id.drawing);
LinearLayout paintLayout = (LinearLayout) getView().findViewById(R.id.paint_colours);
currPaint = (ImageButton)paintLayout.getChildAt(0);
currPaint.setImageDrawable(getResources().getDrawable(R.drawable.paint_pressed));
return getView();
}
// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement OnFragmentInteractionListener");
}
}
@Override
public void onDetach() {
super.onDetach();
mListener = null;
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p/>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public void paintClicked(View view)
{
if(view!=currPaint)
{
ImageButton imgView = (ImageButton)view;
String color = view.getTag().toString();
drawView.setColor(color);
}
}
@Override
public void onClick(View view)
{ //Respond to clicks
if(view.getId()==R.id.draw_btn)
{
final Dialog brushDialog;
brushDialog = new Dialog(getActivity());
brushDialog.setTitle("Brush size:");
brushDialog.setContentView(R.layout.brush_chooser);
ImageButton smallBtn = (ImageButton)brushDialog.findViewById(R.id.small_brush);
smallBtn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
drawView.setBrushSize(smallBrush);
drawView.setLastBrushSize(smallBrush);
brushDialog.dismiss();
}
});
ImageButton mediumBtn = (ImageButton)brushDialog.findViewById(R.id.medium_brush);
mediumBtn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
drawView.setBrushSize(mediumBrush);
drawView.setLastBrushSize(mediumBrush);
brushDialog.dismiss();
}
});
ImageButton largeBtn = (ImageButton)brushDialog.findViewById(R.id.large_brush);
largeBtn.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
drawView.setBrushSize(largeBrush);
drawView.setLastBrushSize(largeBrush);
brushDialog.dismiss();
}
});
brushDialog.show();
}
}
public interface OnFragmentInteractionListener
{
// TODO: Update argument type and name
void onFragmentInteraction(Uri uri);
}
}
这是我得到的错误：
02-06 11:39:00.681 28557-28557/com.example.marlon.fieldapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.marlon.fieldapp, PID: 28557
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.marlon.fieldapp/com.example.marlon.fieldapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2339)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2413)
at android.app.ActivityThread.access$800(ActivityThread.java:155)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1317)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5343)
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:905)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:700)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at com.example.marlon.fieldapp.Field_fragment.onCreate(Field_fragment.java:80)
at android.app.Fragment.performCreate(Fragment.java:2031)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:863)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
at android.app.BackStackRecord.run(BackStackRecord.java:834)
at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1454)
at android.app.Activity.performStart(Activity.java:6025)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2302)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2413)
at android.app.ActivityThread.access$800(ActivityThread.java:155)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1317)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5343)
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:905)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:700)
答案 0 :(得分：1)
在onCreateView中，您应该返回一个膨胀的视图。
获取片段布局的根视图（返回的布局） onCreateView（LayoutInflater，ViewGroup，Bundle）），如果提供的话。
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// Inflate the layout for this fragment
使用提供的inflater来扩充您的布局资源。 像
这样的东西View fragmentView = inflater.inflate(R.layout.frag_view, container, false);
返回fragmentView。
您可能也应该移动
drawBtn = (ImageButton)getView().findViewById(R.id.draw_btn);
到onCreateView。再次，使用膨胀的视图，而不是getView（）。
答案 1 :(得分：0)
在片段中，您不应该访问ui element ion oncreate方法。您必须在oncreateView方法中执行此操作，尝试此代码。
package com.example.marlon.fieldapp;
import android.app.DialogFragment;
import android.content.Context;
import android.graphics.Color;
import android.media.Image;
import android.net.Uri;
import android.os.Bundle;
import android.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageButton;
import android.widget.LinearLayout;
import java.util.UUID;
import android.provider.MediaStore;
import android.app.AlertDialog;
import android.app.Dialog;
import android.content.DialogInterface;
import android.view.View.OnClickListener;
import android.widget.Toast;
/**
* A simple {@link Fragment} subclass.
* Activities that contain this fragment must implement the
* {@link Field_fragment.OnFragmentInteractionListener} interface
* to handle interaction events.
* Use the {@link Field_fragment#newInstance} factory method to
* create an instance of this fragment.
*/
public class Field_fragment extends Fragment implements OnClickListener
{
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
private DrawingView drawView;
private ImageButton currPaint, drawBtn;
private float smallBrush, mediumBrush, largeBrush;
private OnFragmentInteractionListener mListener;
public Field_fragment() {
// Required empty public constructor
}
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @param param2 Parameter 2.
* @return A new instance of fragment Field_fragment.
*/
// TODO: Rename and change types and number of parameters
public static Field_fragment newInstance(String param1, String param2)
{
Field_fragment fragment = new Field_fragment();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
if (getArguments() != null)
{
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
{
// Inflate the layout for this fragment
drawView = (DrawingView) drawView.findViewById(R.id.drawing);
LinearLayout paintLayout = (LinearLayout) getView().findViewById(R.id.paint_colours);
currPaint = (ImageButton)paintLayout.getChildAt(0);
currPaint.setImageDrawable(getResources().getDrawable(R.drawable.paint_pressed));
smallBrush = getResources().getInteger(R.integer.small_size);
mediumBrush = getResources().getInteger(R.integer.medium_size);
largeBrush = getResources().getInteger(R.integer.large_size);
drawBtn = (ImageButton)getView().findViewById(R.id.draw_btn);
drawBtn.setOnClickListener(this);
drawView.setBrushSize(mediumBrush);
return getView();
}
// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement OnFragmentInteractionListener");
}
}
@Override
public void onDetach() {
super.onDetach();
mListener = null;
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p/>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public void paintClicked(View view)
{
if(view!=currPaint)
{
ImageButton imgView = (ImageButton)view;
String color = view.getTag().toString();
drawView.setColor(color);
}
}
@Override
public void onClick(View view)
{ //Respond to clicks
if(view.getId()==R.id.draw_btn)
{
final Dialog brushDialog;
brushDialog = new Dialog(getActivity());
brushDialog.setTitle("Brush size:");
brushDialog.setContentView(R.layout.brush_chooser);
ImageButton smallBtn = (ImageButton)brushDialog.findViewById(R.id.small_brush);
smallBtn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
drawView.setBrushSize(smallBrush);
drawView.setLastBrushSize(smallBrush);
brushDialog.dismiss();
}
});
ImageButton mediumBtn = (ImageButton)brushDialog.findViewById(R.id.medium_brush);
mediumBtn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
drawView.setBrushSize(mediumBrush);
drawView.setLastBrushSize(mediumBrush);
brushDialog.dismiss();
}
});
ImageButton largeBtn = (ImageButton)brushDialog.findViewById(R.id.large_brush);
largeBtn.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
drawView.setBrushSize(largeBrush);
drawView.setLastBrushSize(largeBrush);
brushDialog.dismiss();
}
});
brushDialog.show();
}
}
public interface OnFragmentInteractionListener
{
// TODO: Update argument type and name
void onFragmentInteraction(Uri uri);
}
}
onCreate方法在onCreateView方法之前运行，因此您不应该访问
drawView.setBrushSize(mediumBrush);
在oncreateview
中初始化之前drawView = (DrawingView) drawView.findViewById(R.id.drawing);