在我真正开始研究项目之前,我想练习一下我会考虑Android开发的基本原理。我目前有一个ChipCount
课程,负责保存和加载玩家可能拥有的筹码量。该课程还负责跟踪一般的筹码数量。
我的ChipCount
课程目前看起来如下:
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);
}
}
}
我也有MainActivity
尝试使用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");
}
}
通过评论不同的行,我已确定问题出在int chip = chips.getChips();
行。
为什么这会导致程序崩溃,我怎么可能修复它。
这是logcat:
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
答案 0 :(得分:2)
您永远不会初始化chips
。因此它是null
,因此您无法访问其方法。
而不是ChipCount chips;
,请尝试:ChipCount chips = new ChipCount();
。
注意:此外,将来,当您遇到崩溃时,发布LogCat错误。在这种情况下,这是一个相对简单的修复,但将来可能需要这些日志。
修改强>:
此外,您永远不会将ChipCount
对象传递给file_context
参数。当您在file_context
中调用它时,这会null
loadChips();
。
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_context = newContext;
。
答案 1 :(得分:1)
您从未初始化ChipCount chips;
,因此在调用时它为null,并引发NullPointerException
。
您需要在代码中使用ChipCount chips = new ChipCount();
。