context.getResources()函数

在 Android 开发中，`context.getResources()` 函数用于获取应用程序的资源对象，包括图片、字符串、颜色等等。它返回一个 Resources 类型的对象，你可以使用这个对象获取应用程序的各种资源，例如：

- `getDrawable(int id)` 获取指定 ID 的图片资源；
- `getString(int id)` 获取指定 ID 的字符串资源；
- `getColor(int id)` 获取指定 ID 的颜色资源；
- 等等。

`context` 参数通常传入当前 Activity 或者 Application 的上下文对象。例如，在 Activity 中可以这样使用：

Resources res = getResources();
Drawable drawable = res.getDrawable(R.drawable.my_image);
String str = res.getString(R.string.my_string);

其中 `R.drawable.my_image` 和 `R.string.my_string` 是资源 ID，通过 `getResources()` 函数获取到 `Resources` 对象后，就可以通过这些 ID 获取对应的资源了。

相关问题

Process: com.example.dzy, PID: 26008 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.dzy/com.example.dzy.NavigationActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) at android.os.Handler.dispatchMessage(Handler.java:107) at android.os.Looper.loop(Looper.java:214) at android.app.ActivityThread.main(ActivityThread.java:7356) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference at com.example.dzy.Fragment_1.<init>(Fragment_1.java:44) at com.example.dzy.NavigationActivity.initTab(NavigationActivity.java:39) at com.example.dzy.NavigationActivity.onCreate(NavigationActivity.java:27) at android.app.Activity.performCreate(Activity.java:7802) at android.app.Activity.performCreate(Activity.java:7791) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)

这段错误信息显示了一个 Java 运行时异常，出现了空指针异常，导致无法启动名为 NavigationActivity 的组件。具体地，在 Fragment_1 类的构造函数中，第 44 行代码调用了一个空对象的方法 getResources()，导致了空指针异常。这个错误需要你检查代码中是否正确初始化了上下文对象，确保其不为空。

private final CharSequence getSmallTime() { Context context = getContext(); boolean is24 = DateFormat.is24HourFormat(context); LocaleData d = LocaleData.get(context.getResources().getConfiguration().locale); final char MAGIC1 = '\uEF00'; final char MAGIC2 = '\uEF01'; SimpleDateFormat sdf; String format = is24 ? d.timeFormat24 : d.timeFormat12; // Add seconds to the format string format += ":ss"; if (!format.equals(mClockFormatString)) { /* * Search for an unquoted "a" in the format string, so we can * add dummy characters around it to let us find it again after * formatting and change its size. */ if (AM_PM_STYLE != AM_PM_STYLE_NORMAL) { int a = -1; boolean quoted = false; for (int i = 0; i < format.length(); i++) { char c = format.charAt(i); if (c == ''') { quoted = !quoted; } if (!quoted && c == 'a') { a = i; break; } } if (a >= 0) { // Move a back so any whitespace before AM/PM is also in the alternate size. final int b = a; while (a > 0 && Character.isWhitespace(format.charAt(a-1))) { a--; } format = format.substring(0, a) + MAGIC1 + format.substring(a, b) + "a" + MAGIC2 + format.substring(b + 1); } } mClockFormat = sdf = new SimpleDateFormat(format); mClockFormatString = format; } else { sdf = mClockFormat; } String result = sdf.format(mCalendar.getTime()); if (AM_PM_STYLE != AM_PM_STYLE_NORMAL) { int magic1 = result.indexOf(MAGIC1); int magic2 = result.indexOf(MAGIC2); if (magic1 >= 0 && magic2 > magic1) { SpannableStringBuilder formatted = new SpannableStringBuilder(result); if (AM_PM_STYLE == AM_PM_STYLE_GONE) { formatted.delete(magic1, magic2+1); } else { if (AM_PM_STYLE == AM_PM_STYLE_SMALL) { CharacterStyle style = new RelativeSizeSpan(0.7f); formatted.setSpan(style, magic1, magic2, Spannable.SPAN_EXCLUSIVE_INCLUSIVE); } formatted.delete(magic2, magic2 + 1); formatted.delete(magic1, magic1 + 1); } return formatted; } } return result;}如何实时更新秒

可以通过使用定时器或者Handler来实现每秒更新一次秒数。具体实现方法如下：

1.在构造函数或onCreate()方法中初始化定时器或Handler。

2.定时器或Handler中的回调方法中，调用invalidate()方法刷新UI界面。

示例代码如下：

private final CharSequence getSmallTime() {
    Context context = getContext();
    boolean is24 = DateFormat.is24HourFormat(context);
    LocaleData d = LocaleData.get(context.getResources().getConfiguration().locale);

    final char MAGIC1 = '\uEF00';
    final char MAGIC2 = '\uEF01';

    SimpleDateFormat sdf;
    String format = is24 ? d.timeFormat24 : d.timeFormat12;

    // Add seconds to the format string
    format += ":ss";

    if (!format.equals(mClockFormatString)) {
        /*
         * Search for an unquoted "a" in the format string, so we can
         * add dummy characters around it to let us find it again after
         * formatting and change its size.
         */
        if (AM_PM_STYLE != AM_PM_STYLE_NORMAL) {
            int a = -1;
            boolean quoted = false;
            for (int i = 0; i < format.length(); i++) {
                char c = format.charAt(i);
                if (c == ''') {
                    quoted = !quoted;
                }
                if (!quoted && c == 'a') {
                    a = i;
                    break;
                }
            }
            if (a >= 0) {
                // Move a back so any whitespace before AM/PM is also in the alternate size.
                final int b = a;
                while (a > 0 && Character.isWhitespace(format.charAt(a-1))) {
                    a--;
                }
                format = format.substring(0, a) + MAGIC1 + format.substring(a, b) + "a" + MAGIC2 + format.substring(b + 1);
            }
        }
        mClockFormat = sdf = new SimpleDateFormat(format);
        mClockFormatString = format;
    } else {
        sdf = mClockFormat;
    }

    mCalendar.setTimeInMillis(System.currentTimeMillis()); // 更新Calendar对象

    String result = sdf.format(mCalendar.getTime());

    if (AM_PM_STYLE != AM_PM_STYLE_NORMAL) {
        int magic1 = result.indexOf(MAGIC1);
        int magic2 = result.indexOf(MAGIC2);
        if (magic1 >= 0 && magic2 > magic1) {
            SpannableStringBuilder formatted = new SpannableStringBuilder(result);
            if (AM_PM_STYLE == AM_PM_STYLE_GONE) {
                formatted.delete(magic1, magic2+1);
            } else {
                if (AM_PM_STYLE == AM_PM_STYLE_SMALL) {
                    CharacterStyle style = new RelativeSizeSpan(0.7f);
                    formatted.setSpan(style, magic1, magic2, Spannable.SPAN_EXCLUSIVE_INCLUSIVE);
                }
                formatted.delete(magic2, magic2 + 1);
                formatted.delete(magic1, magic1 + 1);
            }
            return formatted;
        }
    }
    return result;
}

在构造函数或onCreate()方法中添加以下代码：

// 定义Handler
private Handler mHandler = new Handler();

// 定义Runnable
private Runnable mRunnable = new Runnable() {
    @Override
    public void run() {
        invalidate(); // 刷新UI界面
        mHandler.postDelayed(mRunnable, 1000); // 每秒执行一次
    }
};

// 在构造函数或onCreate()方法中启动定时器
mHandler.postDelayed(mRunnable, 1000);

这样就可以实现每秒更新秒数了。