Java 在android活动中使用外部类 我想在我开始着手一个项目之前实践我所认为的Android开发的基本原理。我目前有一个ChipCount类,负责保存和加载玩家将拥有的芯片数量。该课程还将负责跟踪芯片的数量
我的Java 在android活动中使用外部类 我想在我开始着手一个项目之前实践我所认为的Android开发的基本原理。我目前有一个ChipCount类,负责保存和加载玩家将拥有的芯片数量。该课程还将负责跟踪芯片的数量,java,android,Java,Android,我的ChipCount类当前看起来如下所示: package com.example.parceltest; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import android.content.Context; public class ChipCount { private int number_of_chips; Cont
ChipCount
类当前看起来如下所示:
package com.example.parceltest;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import android.content.Context;
public class ChipCount {
private int number_of_chips;
Context file_context;
public ChipCount() {
loadChips();
}
public void setChips(int chips) {
this.number_of_chips = chips;
}
public int getChips() {
return number_of_chips;
}
public void saveChips() {
String filename = "chipsave";
String save_string = String.valueOf(number_of_chips);
try {
FileOutputStream output = file_context.getApplicationContext().openFileOutput(filename, Context.MODE_PRIVATE);
output.write(save_string.getBytes());
output.close();
} catch(IOException e) {
}
}
public void loadChips() {
String filename = "chipsave";
String chip_count = "";
try {
FileInputStream input = file_context.getApplicationContext().openFileInput(filename);
input.read(chip_count.getBytes());
} catch(IOException e) {
this.setChips(500);
}
}
}
我还有main活动
,它试图利用ChipCount
,但它崩溃了
package com.example.parceltest;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
public class MainActivity extends Activity {
ChipCount chips = new ChipCount();
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView number_of_chips = (TextView) findViewById(R.id.number_of_chips);
int chip = chips.getChips();
//number_of_chips.setText("500");
}
}
通过注释不同的行,我已经确定问题出在int chip=chips.getChips()行代码>
为什么这会使程序崩溃,我怎么可能修复它
这是日志:
10-01 22:51:06.958: I/Process(28051): Sending signal. PID: 28051 SIG: 9
10-01 22:51:26.669: D/AndroidRuntime(28106): Shutting down VM
10-01 22:51:26.669: W/dalvikvm(28106): threadid=1: thread exiting with uncaught exception (group=0x40b7c300)
10-01 22:51:26.669: E/AndroidRuntime(28106): FATAL EXCEPTION: main
10-01 22:51:26.669: E/AndroidRuntime(28106): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.parceltest/com.example.parceltest.MainActivity}: java.lang.NullPointerException
10-01 22:51:26.669: E/AndroidRuntime(28106): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
10-01 22:51:26.669: E/AndroidRuntime(28106): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
10-01 22:51:26.669: E/AndroidRuntime(28106): at android.app.ActivityThread.access$600(ActivityThread.java:130)
10-01 22:51:26.669: E/AndroidRuntime(28106): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
10-01 22:51:26.669: E/AndroidRuntime(28106): at android.os.Handler.dispatchMessage(Handler.java:99)
10-01 22:51:26.669: E/AndroidRuntime(28106): at android.os.Looper.loop(Looper.java:137)
10-01 22:51:26.669: E/AndroidRuntime(28106): at android.app.ActivityThread.main(ActivityThread.java:4745)
10-01 22:51:26.669: E/AndroidRuntime(28106): at java.lang.reflect.Method.invokeNative(Native Method)
10-01 22:51:26.669: E/AndroidRuntime(28106): at java.lang.reflect.Method.invoke(Method.java:511)
10-01 22:51:26.669: E/AndroidRuntime(28106): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
10-01 22:51:26.669: E/AndroidRuntime(28106): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-01 22:51:26.669: E/AndroidRuntime(28106): at dalvik.system.NativeStart.main(Native Method)
10-01 22:51:26.669: E/AndroidRuntime(28106): Caused by: java.lang.NullPointerException
10-01 22:51:26.669: E/AndroidRuntime(28106): at com.example.parceltest.ChipCount.loadChips(ChipCount.java:45)
10-01 22:51:26.669: E/AndroidRuntime(28106): at com.example.parceltest.ChipCount.<init>(ChipCount.java:15)
10-01 22:51:26.669: E/AndroidRuntime(28106): at com.example.parceltest.MainActivity.<init>(MainActivity.java:9)
10-01 22:51:26.669: E/AndroidRuntime(28106): at java.lang.Class.newInstanceImpl(Native Method)
10-01 22:51:26.669: E/AndroidRuntime(28106): at java.lang.Class.newInstance(Class.java:1319)
10-01 22:51:26.669: E/AndroidRuntime(28106): at android.app.Instrumentation.newActivity(Instrumentation.java:1053)
10-01 22:51:26.669: E/AndroidRuntime(28106): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974)
10-01 22:51:26.669: E/AndroidRuntime(28106): ... 11 more
10-01 22:51:06.958:I/进程(28051):发送信号。PID:28051信号:9
10-01 22:51:26.669:D/AndroidRuntime(28106):关闭虚拟机
10-01 22:51:26.669:W/dalvikvm(28106):threadid=1:线程退出,但出现未捕获异常(组=0x40b7c300)
10-01 22:51:26.669:E/AndroidRuntime(28106):致命异常:main
10-01 22:51:26.669:E/AndroidRuntime(28106):java.lang.RuntimeException:无法实例化活动组件信息{com.example.parceltest/com.example.parceltest.MainActivity}:java.lang.NullPointerException
10-01 22:51:26.669:E/AndroidRuntime(28106):在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
10-01 22:51:26.669:E/AndroidRuntime(28106):在android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
10-01 22:51:26.669:E/AndroidRuntime(28106):在android.app.ActivityThread.access$600(ActivityThread.java:130)
10-01 22:51:26.669:E/AndroidRuntime(28106):在android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
10-01 22:51:26.669:E/AndroidRuntime(28106):位于android.os.Handler.dispatchMessage(Handler.java:99)
10-01 22:51:26.669:E/AndroidRuntime(28106):在android.os.Looper.loop(Looper.java:137)
10-01 22:51:26.669:E/AndroidRuntime(28106):位于android.app.ActivityThread.main(ActivityThread.java:4745)
10-01 22:51:26.669:E/AndroidRuntime(28106):位于java.lang.reflect.Method.Invokenactive(本机方法)
10-01 22:51:26.669:E/AndroidRuntime(28106):位于java.lang.reflect.Method.invoke(Method.java:511)
10-01 22:51:26.669:E/AndroidRuntime(28106):在com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
10-01 22:51:26.669:E/AndroidRuntime(28106):位于com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-01 22:51:26.669:E/AndroidRuntime(28106):在dalvik.system.NativeStart.main(本机方法)
10-01 22:51:26.669:E/AndroidRuntime(28106):由以下原因引起:java.lang.NullPointerException
10-01 22:51:26.669:E/AndroidRuntime(28106):在com.example.parceltest.ChipCount.loadChips(ChipCount.java:45)
10-01 22:51:26.669:E/AndroidRuntime(28106):在com.example.parceltest.ChipCount.(ChipCount.java:15)
10-01 22:51:26.669:E/AndroidRuntime(28106):在com.example.parceltest.MainActivity。(MainActivity.java:9)
10-01 22:51:26.669:E/AndroidRuntime(28106):位于java.lang.Class.newInstanceImpl(本机方法)
10-01 22:51:26.669:E/AndroidRuntime(28106):位于java.lang.Class.newInstance(Class.java:1319)
10-01 22:51:26.669:E/AndroidRuntime(28106):在android.app.Instrumentation.newActivity(Instrumentation.java:1053)上
10-01 22:51:26.669:E/AndroidRuntime(28106):在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974)
10-01 22:51:26.669:E/AndroidRuntime(28106):。。。还有11个
您从未初始化过芯片计数芯片
,因此调用时为null,并引发NullPointerException
您需要像ChipCount chips=new ChipCount()代码>在您的代码中。您从未初始化芯片。因此它是null
,因此您无法访问它的方法
而不是ChipCount芯片代码>,尝试:ChipCount chips=new ChipCount()代码>
注意:另外,将来发生崩溃时,请发布LogCat错误。在本例中,这是一个相对简单的修复,但这些日志在将来可能是必需的
编辑:
此外,您永远不会将ChipCount
对象传递给file\u context
参数。当您在loadChips()中调用file\u context时,它会使file\u context
null
代码>
试试这个:
public class MainActivity extends Activity {
ChipCount chips; // Don't initialize here, on second thought
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
chips = new ChipCount(this); // Initialize here; and pass it `this`, which is an Activity, and also a Context
TextView number_of_chips = (TextView) findViewById(R.id.number_of_chips);
int chip = chips.getChips();
//number_of_chips.setText("500");
}
}
然后,在ChipCount
的构造函数中,接受Context
参数,然后执行file\u Context=newContext代码>即使更改了该行,应用程序在启动时仍然强制关闭。它不应该关闭。如果是,则是另一个错误代码。是否要用编辑后的代码和LogCat输出编辑您的第一篇文章?@lafferjm我已更新了我的答案,以解决您发布的日志。感谢您解决了此问题。请尝试双击“原因:…”行后的第一行,它将带您到导致您NPE的行。