当我尝试打开此页面时，它会崩溃。我试图让这个按钮以各种方式计数，但无法计算！我已经尝试过各种各样的教程，但是它对我不起作用。
package com.fullcyclestudios.rust;
import android.support.v7.app.ActionBarActivity;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.app.Activity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;
import android.content.Intent;
public class Medical extends ActionBarActivity {
Button add, sub;
int counter;
TextView textView;
TextView quantityDisplay;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_medical);
add=(Button) findViewById(R.id.addButtonMedical);
sub=(Button) findViewById(R.id.minusButtonMedical);
quantityDisplay = (TextView) findViewById(R.id.textViewQuantityMedical);
counter=1;
add.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View arg0)
{
// TODO Auto-generated method stub
counter++;
quantityDisplay.setText("it"+counter);
}
});
sub.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v)
{
// TODO Auto-generated method stub
counter--;
quantityDisplay.setText("it"+counter);
}
});
Intent intent = getIntent();
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.medical, 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();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_medical,
container, false);
return rootView;
}
}
/** Bandage button */
public String bandageMaterials(View view)
{
String materials = "Bandage\r\n\r\n2 Cloth";
textView = (TextView) findViewById(R.id.textViewMatMedical);
textView.setText(materials);
return materials;
}
/** Small Medkit button */
public String smallMedkitMaterials(View view)
{
String materials = "Small Medkit\r\n\r\n2 Cloth\r\n2 Blood";
textView = (TextView) findViewById(R.id.textViewMatMedical);
textView.setText(materials);
return materials;
}
/** Large Medkit button */
public String largeMedkitMaterials(View view)
{
String materials = "Large Medkit\r\n\r\n3 Cloth\r\n3 Blood";
textView = (TextView) findViewById(R.id.textViewMatMedical);
textView.setText(materials);
return materials;
}
}
<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:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.fullcyclestudios.rust.Medical$PlaceholderFragment" >
<ScrollView
android:id="@+id/scrollViewMedical"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="130dp" >
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical" >
<Button
android:id="@+id/bandageButton"
style="?android:attr/buttonStyleSmall"
android:layout_width="150dp"
android:layout_height="35dp"
android:text="@string/bandage"
android:onClick="bandageMaterials" />
<Button
android:id="@+id/smallMedkitButton"
style="?android:attr/buttonStyleSmall"
android:layout_width="150dp"
android:layout_height="35dp"
android:text="@string/smallMedkit"
android:onClick="smallMedkitMaterials" />
<Button
android:id="@+id/largeMedkitButton"
style="?android:attr/buttonStyleSmall"
android:layout_width="150dp"
android:layout_height="35dp"
android:text="@string/largeMedkit"
android:onClick="largeMedkitMaterials" />
</LinearLayout>
</ScrollView>
<TextView
android:id="@+id/textViewMatMedical"
android:layout_width="120dp"
android:layout_height="fill_parent"
android:layout_marginTop="140dp"
android:background="@color/gray"
android:text="@string/blank" />
<TextView
android:id="@+id/textViewQuantityMedical"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/minusButtonMedical"
android:layout_alignRight="@+id/minusButtonMedical"
android:layout_below="@+id/addButtonMedical"
android:gravity="center_horizontal"
android:text="@string/one"
android:textAppearance="?android:attr/textAppearanceSmall"
android:textSize="25sp" />
<Button
android:id="@+id/minusButtonMedical"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="50dp"
android:layout_marginTop="80dp"
android:layout_alignLeft="@+id/addButtonMedical"
android:layout_alignRight="@+id/addButtonMedical"
android:text="@string/minus"
android:textSize="30sp"
android:textStyle="bold" />
<Button
android:id="@+id/addButtonMedical"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="50dp"
android:layout_alignLeft="@+id/textViewMatMedical"
android:layout_alignRight="@+id/textViewMatMedical"
android:text="@string/add"
android:textSize="30sp" />
</RelativeLayout>
06-08 16:10:38.890: W/dalvikvm(855): threadid=1: thread exiting with uncaught exception (group=0xb2a40ba8)
06-08 16:10:38.990: E/AndroidRuntime(855): FATAL EXCEPTION: main
06-08 16:10:38.990: E/AndroidRuntime(855): Process: com.fullcyclestudios.rust, PID: 855
06-08 16:10:38.990: E/AndroidRuntime(855): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.fullcyclestudios.rust/com.fullcyclestudios.rust.Medical}: java.lang.NullPointerException
06-08 16:10:38.990: E/AndroidRuntime(855): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.app.ActivityThread.access$800(ActivityThread.java:135)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.os.Handler.dispatchMessage(Handler.java:102)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.os.Looper.loop(Looper.java:136)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.app.ActivityThread.main(ActivityThread.java:5017)
06-08 16:10:38.990: E/AndroidRuntime(855): at java.lang.reflect.Method.invokeNative(Native Method)
06-08 16:10:38.990: E/AndroidRuntime(855): at java.lang.reflect.Method.invoke(Method.java:515)
06-08 16:10:38.990: E/AndroidRuntime(855): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
06-08 16:10:38.990: E/AndroidRuntime(855): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
06-08 16:10:38.990: E/AndroidRuntime(855): at dalvik.system.NativeStart.main(Native Method)
06-08 16:10:38.990: E/AndroidRuntime(855): Caused by: java.lang.NullPointerException
06-08 16:10:38.990: E/AndroidRuntime(855): at com.fullcyclestudios.rust.Medical.onCreate(Medical.java:33)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.app.Activity.performCreate(Activity.java:5231)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
06-08 16:10:38.990: E/AndroidRuntime(855): ... 11 more
06-08 16:10:43.330: I/Process(855): Sending signal. PID: 855 SIG: 9
答案 0 :(得分：0)
您的问题在这里：
的setContentView（R.layout.activity_medical）;
add=(Button) findViewById(R.id.addButtonMedical);
sub=(Button) findViewById(R.id.minusButtonMedical);
但是你发布的内容：addButtonMedical和minusButtonMedical都在fragment_medical里面而不是activity_medical xml布局！