Java-Android MediaRecorder NullPointerException
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我刚开始使用Java开发,并且在摆弄Android Media记录器.但是我得到了一个N??ullPointerException,它使用以下源代码单击了记录按钮：
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
//import android.net.Uri;
import android.view.Menu;
import android.view.MenuItem;
import android.os.Environment;
import android.view.View;
import java.io.File;
import java.io.IOException;
import android.media.MediaPlayer;
import android.media.MediaRecorder;
import java.lang.String;
public class MainActivity extends ActionBarActivity {
String outputFile = "test.3gp";
private MediaRecorder myAudioRecorder;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
MediaRecorder myAudioRecorder = new MediaRecorder();
myAudioRecorder = new MediaRecorder();
// Uri target = Uri.parse(outputFile.getAbsolutePath());
myAudioRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
myAudioRecorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
myAudioRecorder.setAudioEncoder(MediaRecorder.OutputFormat.AMR_NB);
myAudioRecorder.setOutputFile(outputFile);
}
public void Start_Record(View v)
{
try {
myAudioRecorder.prepare();
myAudioRecorder.start();
} catch (IllegalStateException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
myAudioRecorder.stop();
myAudioRecorder.release();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
我意识到这可能是由于将填充指针设置为NULL所致,但是我正在努力查看如何初始化文件引用以使其消失.我在mediaRecorderPrepare()上遇到异常
这是抛出的异常：
03-09 22:53:56.548 31836-31836/uk.co.spectralgear.spectralboost E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.IllegalStateException: Could not execute method of the activity
at android.view.View$1.onClick(View.java:4007)
at android.view.View.performClick(View.java:4756)
at android.view.View$PerformClick.run(View.java:19749)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at android.view.View$1.onClick(View.java:4002)
????????????at android.view.View.performClick(View.java:4756)
????????????at android.view.View$PerformClick.run(View.java:19749)
????????????at android.os.Handler.handleCallback(Handler.java:739)
????????????at android.os.Handler.dispatchMessage(Handler.java:95)
????????????at android.os.Looper.loop(Looper.java:135)
????????????at android.app.ActivityThread.main(ActivityThread.java:5221)
????????????at java.lang.reflect.Method.invoke(Native Method)
????????????at java.lang.reflect.Method.invoke(Method.java:372)
????????????at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
????????????at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.media.MediaRecorder.prepare()' on a null object reference
at uk.co..MainActivity.Start_Record(MainActivity.java:38)
????????????at java.lang.reflect.Method.invoke(Native Method)
????????????at java.lang.reflect.Method.invoke(Method.java:372)
????????????at android.view.View$1.onClick(View.java:4002)
????????????at android.view.View.performClick(View.java:4756)
????????????at android.view.View$PerformClick.run(View.java:19749)
????????????at android.os.Handler.handleCallback(Handler.java:739)
????????????at android.os.Handler.dispatchMessage(Handler.java:95)
????????????at android.os.Looper.loop(Looper.java:135)
????????????at android.app.ActivityThread.main(ActivityThread.java:5221)
????????????at java.lang.reflect.Method.invoke(Native Method)
????????????at java.lang.reflect.Method.invoke(Method.java:372)
????????????at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
????????????at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
任何帮助将不胜感激：)
解决方法:
问题：
当“ Start_Record()”尝试使用它时,您的类变量“ myAudioRecord”为空：
Caused by: java.lang.NullPointerException:
Attempt to invoke virtual method 'void Android.media.MediaRecorder.prepare()' on a null object reference
解决方案：从“ onCreate()”方法中删除此行：
public class MainActivity extends ActionBarActivity {
String outputFile = "test.3gp";
private MediaRecorder myAudioRecorder; // Your class variable: OK...
@Override
protected void onCreate(Bundle savedInstanceState) {
...
// MediaRecorder myAudioRecorder = new MediaRecorder(); // DELETE THIS LINE!!!
myAudioRecorder = new MediaRecorder(); // OK...
...
onCreate()内部的“ myAudioRecorder”声明隐藏了外部声明.因此,外部(类级别)“ myAudioRecorder”永远不会初始化…并且当“ Start_Record()”尝试访问它时,您的程序会与NPE一起死掉.
PS：
请考虑将方法名称更改为“ start_Record()”.或者更好的是“ startRecord()”.这与Java命名约定更加一致.
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