安卓：我怎么叫这是存在于其他API级别的方法？ [英] Android: How do I call a method which is existing in other API Level?

问题描述

我的应用程序采用了Android 2.1它利用LocationManager获得高度。但现在，我需要获得使用的SensorManager的海拔高度需要API 9级（2.3）。

I have application using Android 2.1 which utilize LocationManager to get the altitude. But now, I need to obtain the altitude using SensorManager which requires API Level 9 (2.3).

我怎样才能把 SensorManager.getAltitude（浮动，浮动）在我的2.1 Android应用程序通过将一个条件，并通过函数名调用它（可能在正常的Java ）？

How can I put the SensorManager.getAltitude(float, float) in my 2.1 android application by putting a condition and calling it by a function name (possible in normal Java)?

感谢你在前进

更新1 如果你已经注意到，我的应用程序需要使用Android 2.1的编译。这就是为什么我在寻找一种通过名称或可编译任何其他方式调用该函数。

UPDATE 1 If you have noticed that my application need to be compiled using Android 2.1. That's why I'm looking for a way to call the function by name or in any other way that can be compiled.

推荐答案

您可以调用使用反射的方法，未能在正常的情况下错误（如缺少类或方法）的。请参阅<一href="http://download.oracle.com/javase/6/docs/api/java/lang/reflect/package-summary.html">java.lang.reflect

You can call the method using reflection and fail gracefully in case of errors (like missing class or methods). See java.lang.reflect

另一种选择是编译code。在9水平，但与周围的try / catch赶上，将源于执行较低的水平上的错误。它可以很容易出错，不过，我会三思这样做。

Other option is to compile code in level 9 but surround with try/catch to catch errors that would arise from execution on lower level. It could be fairly error prone, though, and I'd think twice about doing it.

更新

下面是测试code

public void onCreate(Bundle savedInstanceState)
{
    try {
        // First we try reflection approach.
        // Expected result
        //    in 2.3 we print some value in log but no exception
        //    in 2.2 we print NoSuchMethodException
        // In both levels we get our screen displayed after catch
        Method m = SensorManager.class.getMethod("getAltitude",Float.TYPE, Float.TYPE);
        Float a = (Float)m.invoke(null, 0.0f, 0.0f);
        Log.w("test","Result 1: " + a);
    } catch (Throwable e) {
        Log.e("test", "error 1",e);
    }

    try {
        // Now we try compiling against 2.3
        // Expected result
        //    in 2.3 we print some value in log but no exception
        //    in 2.2 we print NoSuchMethodError (Note that it is an error not exception but it's still caught)
        // In both levels we get our screen displayed after catch
        float b = SensorManager.getAltitude(0.0f, 0.0f);
        Log.w("test","Result 2: " + b);

    } catch (Throwable e) {
        Log.e("test", "error 2",e);
    }

    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
}

结果：

2.3

09-14 07:04:50.374: DEBUG/dalvikvm(589): Debugger has detached; object registry had 1 entries
09-14 07:04:50.924: WARN/test(597): Result 1: NaN
09-14 07:04:51.014: WARN/test(597): Result 2: NaN
09-14 07:04:51.384: INFO/ActivityManager(75): Displayed com.example/.MyActivity: +1s65ms

2.2

09-14 07:05:48.220: INFO/dalvikvm(382): Could not find method android.hardware.SensorManager.getAltitude, referenced from method com.example.MyActivity.onCreate
09-14 07:05:48.220: WARN/dalvikvm(382): VFY: unable to resolve static method 2: Landroid/hardware/SensorManager;.getAltitude (FF)F
09-14 07:05:48.220: DEBUG/dalvikvm(382): VFY: replacing opcode 0x71 at 0x0049
09-14 07:05:48.220: DEBUG/dalvikvm(382): VFY: dead code 0x004c-0064 in Lcom/example/MyActivity;.onCreate (Landroid/os/Bundle;)V
09-14 07:05:48.300: ERROR/test(382): error 1
        java.lang.NoSuchMethodException: getAltitude
        at java.lang.ClassCache.findMethodByName(ClassCache.java:308)

跳过堆栈跟踪

Skipped stack trace

09-14 07:05:48.300: ERROR/test(382): error 2
    java.lang.NoSuchMethodError: android.hardware.SensorManager.getAltitude
    at com.example.MyActivity.onCreate(MyActivity.java:35)

更多跳过堆栈跟踪

Skipped more stack trace

09-14 07:05:48.330: DEBUG/dalvikvm(33): GC_EXPLICIT freed 2 objects / 64 bytes in 180ms
09-14 07:05:48.520: INFO/ActivityManager(59): Displayed activity com.example/.MyActivity: 740 ms (total 740 ms)

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