我是新来的，也是Android开发的新手，刚刚开始学习， 涵盖了一些概念并开始研究我的第一个应用程序，但感叹，错误 到处都是错误我用Google搜索但没有找到我能理解的解决方案， 也许是因为我是新的以及我看到的其他堆栈溢出页面 压倒性的代码和解决方案
在我尝试构建的第一个应用程序上，错误立即开始。
这是我的日志：
06/26 09:43:01: Launching app
Cold swapped changes.
$ adb shell am start -n "com.example.android.cricketcounter/com.example.android.cricketcounter.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER -D
Waiting for application to come online: com.example.android.cricketcounter.test | com.example.android.cricketcounter
Waiting for application to come online: com.example.android.cricketcounter.test | com.example.android.cricketcounter
Waiting for application to come online: com.example.android.cricketcounter.test | com.example.android.cricketcounter
Connecting to com.example.android.cricketcounter
W/ActivityThread: Application com.example.android.cricketcounter is waiting for the debugger on port 8100...
I/System.out: Sending WAIT chunk
I/art: Debugger is active
I/System.out: Debugger has connected
I/System.out: waiting for debugger to settle...
Connected to the target VM, address: 'localhost:8611', transport: 'socket'
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: waiting for debugger to settle...
I/System.out: debugger has settled (1499)
W/System: ClassLoader referenced unknown path: /data/app/com.example.android.cricketcounter-1/lib/x86
I/InstantRun: Instant Run Runtime started. Android package is com.example.android.cricketcounter, real application class is null.
W/System: ClassLoader referenced unknown path: /data/app/com.example.android.cricketcounter-1/lib/x86
W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
I/art: Do partial code cache collection, code=18KB, data=21KB
I/art: After code cache collection, code=18KB, data=21KB
I/art: Increasing code cache capacity to 128KB
I/art: Do partial code cache collection, code=18KB, data=40KB
I/art: After code cache collection, code=18KB, data=40KB
I/art: Increasing code cache capacity to 256KB
I/art: JIT allocated 61KB for compiled code of void android.widget.TextView.<init>(android.content.Context, android.util.AttributeSet, int, int)
I/art: Compiler allocated 4MB to compile void android.widget.TextView.<init>(android.content.Context, android.util.AttributeSet, int, int)
[ 06-26 09:43:05.790 5001: 5001 D/ ]
HostConnection::get() New Host Connection established 0xa6c3a180, tid 5001
[ 06-26 09:43:05.865 5001: 5020 D/ ]
HostConnection::get() New Host Connection established 0xa6ccb9c0, tid 5020
I/OpenGLRenderer: Initialized EGL, version 1.4
D/OpenGLRenderer: Swap behavior 1
W/OpenGLRenderer: Failed to choose config with EGL_SWAP_BEHAVIOR_PRESERVED, retrying without...
D/OpenGLRenderer: Swap behavior 0
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.android.cricketcounter, PID: 5001
java.lang.IllegalStateException: Could not execute method for android:onClick
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
at android.view.View.performClick(View.java:5610)
at android.view.View$PerformClick.run(View.java:22265)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:5610)
at android.view.View$PerformClick.run(View.java:22265)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at com.example.android.cricketcounter.MainActivity.runsScored(MainActivity.java:20)
at com.example.android.cricketcounter.MainActivity.addSix(MainActivity.java:25)
at java.lang.reflect.Method.invoke(Native Method)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:5610)
at android.view.View$PerformClick.run(View.java:22265)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Disconnected from the target VM, address: 'localhost:8611', transport: 'socket'
这是xml文件：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.android.cricketcounter.MainActivity">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center_horizontal"
android:text="Cricket scores"
android:textSize="20dp" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center_horizontal">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Score: "
android:textSize="40dp" />
<TextView
android:id="@+id/runs"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="0"
android:textSize="40dp" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="/"
android:textSize="40dp" />
<TextView
android:id="@+id/wickets"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="0"
android:textSize="40dp" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center_horizontal">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Balls: "
android:textSize="40dp" />
<TextView
android:id="@+id/balls"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="0"
android:textSize="40dp" />
</LinearLayout>
</LinearLayout>
<Button
android:id="@+id/reset_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="40dp"
android:text="Reset" />
<LinearLayout
android:id="@+id/other_buttons"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_above="@id/reset_button">
<Button
android:id="@+id/six_runs"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:onClick="addSix"
android:text="+6" />
<Button
android:id="@+id/no_ball"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="No ball"
android:textSize="13sp" />
<Button
android:id="@+id/wide_ball"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Wide" />
<Button
android:id="@+id/out"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="out" />
<Button
android:id="@+id/dot_ball"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Dot" />
</LinearLayout>
<LinearLayout
android:id="@+id/runs_buttons"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_above="@id/other_buttons">
<Button
android:id="@+id/one_run"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="+1" />
<Button
android:id="@+id/two_runs"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="+2" />
<Button
android:id="@+id/three_runs"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="+3" />
<Button
android:id="@+id/four_runs"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="+4" />
<Button
android:id="@+id/five_runs"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="+5" />
</LinearLayout>
</RelativeLayout>
和java文件：
package com.example.android.cricketcounter;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
int runs = 0;
public void runsScored(int runsa) {
TextView scoreView = (TextView) findViewById(runs);
scoreView.setText(String.valueOf(runsa));
}
public void addSix(View v) {
runs = runs + 6;
runsScored(runs);
}
}
注意：java文件仍然不完整，但足以使其中一个按钮起作用
答案 0 :(得分：4)
此处发生NullPointerException：
TextView scoreView = (TextView) findViewById(runs);
TextView scoreView = (TextView) findViewById(R.id.runs);