java - 安卓Java : Activity doesn't start when the used SharedPreferences

Question

我有一个问题。我想读取 GPSTracker 服务中 Activity “设置”的值整数并在那里使用它。我使用这个 SharedPrefences 并确认按键输入。如果数据经过验证，则应用程序返回类 FullscreenActivity。 这是 Activity 设置中负责此操作的代码:

    SharedPreferences.Editor editor;
    public static final String NAME = "DISTANCE";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_settings);
    final View controlsView = findViewById(R.id.fullscreen_content_controls);
    final View contentView = findViewById(R.id.fullscreen_content);

    SharedPreferences pref = getApplicationContext().getSharedPreferences(NAME, MODE_PRIVATE);
    editor=pref.edit();

    Edit1= (EditText) findViewById(R.id.editSkan);
    accept= (Button) findViewById(R.id.buttonSkan);
    accept.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View arg0) {
            if (!Edit1.getText().toString().equals(""))
                value = Integer.parseInt(Edit1.getText().toString());
            editor.putInt("settings", value);
            editor.commit();

            Toast.makeText(getApplicationContext(), "Changed, value + " m", Toast.LENGTH_SHORT).show();
            finish();
        }
    });

GPSTracker 中的代码如下:

      SharedPreferences pref;

(...)

    private int downloadSettings()
    {
        pref=context.getSharedPreferences("DISTANCE", Activity.MODE_PRIVATE);
        value = pref.getInt("settings",15); 

        return value;
    }

和方法调用:

    int dist = downloadSettings();

当我运行应用程序时，我在日志中收到两个错误:

*java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.adam.mobileproject/com.example.adam.mobileproject.FullscreenActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5001)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.example.adam.mobileproject.GPSTracker.downloadSettings(GPSTracker.java:284)
            at com.example.adam.mobileproject.GPSTracker.<init>(GPSTracker.java:200)
            at com.example.adam.mobileproject.FullscreenActivity.onCreate(FullscreenActivity.java:40)
            at android.app.Activity.performCreate(Activity.java:5231)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5001)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
            at dalvik.system.NativeStart.main(Native Method)*

请帮忙!!!

Answer 1

问题肯定是 context 为空。

但是，就像 Activity 类一样，Service 类扩展了 Context，因此您应该能够将 context 替换为 this 或 getApplicationContext()。

试试这个:

private int downloadSettings()
{
    pref = getApplicationContext().getSharedPreferences("DISTANCE", Activity.MODE_PRIVATE);
    value = pref.getInt("settings",15); 

    return value;
}