为什么“System.out。”println“工作在Android?

我想在控制台打印一些东西，这样我就可以调试它。但出于某种原因，我的Android应用程序没有打印任何东西。

我怎么调试呢?

public class HelloWebview extends Activity {
    WebView webview;    
    private static final String LOG_TAG = "WebViewDemo";
    private class HelloWebViewClient extends WebViewClient {
        @Override
        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            view.loadUrl(url);
            return true;
        }
    }

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        webview = (WebView) findViewById(R.id.webview);
        webview.setWebViewClient(new HelloWebViewClient());
        webview.getSettings().setJavaScriptEnabled(true);
        webview.setWebChromeClient(new MyWebChromeClient());
        webview.loadUrl("http://example.com/");    
        System.out.println("I am here");
    }

当前回答

Correction: On the emulator and most devices System.out.println gets redirected to LogCat and printed using Log.i(). This may not be true on very old or custom Android versions. Original: There is no console to send the messages to so the System.out.println messages get lost. In the same way this happens when you run a "traditional" Java application with javaw. Instead, you can use the Android Log class: Log.d("MyApp","I am here"); You can then view the log either in the Logcat view in Eclipse, or by running the following command: adb logcat It's good to get in to the habit of looking at logcat output as that is also where the Stack Traces of any uncaught Exceptions are displayed. The first Entry to every logging call is the log tag which identifies the source of the log message. This is helpful as you can filter the output of the log to show just your messages. To make sure that you're consistent with your log tag it's probably best to define it once as a static final String somewhere. Log.d(MyActivity.LOG_TAG,"Application started"); There are five one-letter methods in Log corresponding to the following levels: e() - Error w() - Warning i() - Information d() - Debug v() - Verbose wtf() - What a Terrible Failure The documentation says the following about the levels: Verbose should never be compiled into an application except during development. Debug logs are compiled in but stripped at runtime. Error, warning and info logs are always kept.

2010-02-08 09:27:10

其他回答

当然，要在logcat中看到结果，您应该至少将日志级别设置为“Info”(logcat中的日志级别);否则，就像我遇到的那样，您将看不到您的输出。

2016-01-27 08:24:15

是的。如果您正在使用模拟器，它将显示在系统下的Logcat视图中。标签。编写一些东西并在模拟器中进行尝试。

2012-04-20 08:53:35

它没有显示在您的应用程序中…它在模拟器的logcat下

2019-07-24 08:37:58

如果你真的需要System.out.println工作(例如。它是从第三方库调用的)。你可以简单地使用反射来更改System.class中的out字段:

try{
    Field outField = System.class.getDeclaredField("out");
    Field modifiersField = Field.class.getDeclaredField("accessFlags");
    modifiersField.setAccessible(true);
    modifiersField.set(outField, outField.getModifiers() & ~Modifier.FINAL);
    outField.setAccessible(true);
    outField.set(null, new PrintStream(new RedirectLogOutputStream()); 
}catch(NoSuchFieldException e){
    e.printStackTrace(); 
}catch(IllegalAccessException e){
    e.printStackTrace(); 
}

RedirectLogOutputStream类:

public class RedirectLogOutputStream extends OutputStream{
    private String mCache;

    @Override
    public void write(int b) throws IOException{
        if(mCache == null) mCache = "";

        if(((char) b) == '\n'){
            Log.i("redirect from system.out", mCache);
            mCache = "";
        }else{
            mCache += (char) b;
        }
    }
}

2017-03-16 09:16:40

你的手机上没有地方可以读取System.out.println();

相反，如果你想查看某些结果，要么查看你的logcat/控制台窗口，要么让Toast或Snackbar(如果你在较新的设备上)出现在设备的屏幕上，并显示消息:) 这就是我所做的，当我必须检查例如它在开关情况代码!祝你编码愉快!：）

2016-12-24 10:24:33

为什么“System.out。”println“工作在Android?

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