设置Textview时的Android java.lang.NullPointerException [重复]

Question

这个问题在这里已有答案：

• What is a NullPointerException, and how do I fix it? 12个答案

我一直在关注我发现的一个例子，当做最简单的事情时，在Textview中设置文本它会给我一个错误，我将在下面显示。最常见的问题是在视图膨胀之前分配了textview，但这不是这种情况并且更改，尝试不同的布局也不起作用。我相信我在这里有一件简单的事情，但有人能告诉我它是什么。

public class MainActivity extends AppCompatActivity {

TextView pitchText, noteText;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    AudioDispatcher dispatcher =
            AudioDispatcherFactory.fromDefaultMicrophone(22050,1024,0);

    pitchText = (TextView) findViewById(R.id.pitchText);
    pitchText = (TextView) findViewById(R.id.noteText);

    PitchDetectionHandler pdh = new PitchDetectionHandler() {
        @Override
        public void handlePitch(PitchDetectionResult res, AudioEvent e){
            final float pitchInHz = res.getPitch();
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    processPitch(pitchInHz);
                }
            });
        }
    };
    AudioProcessor pitchProcessor = new PitchProcessor(PitchProcessor.PitchEstimationAlgorithm.FFT_YIN, 22050, 1024, pdh);
    dispatcher.addAudioProcessor(pitchProcessor);

    Thread audioThread = new Thread(dispatcher, "Audio Thread");
    audioThread.start();

}

public void processPitch(float pitchInHz) {

    pitchText.setText("" + pitchInHz);

    if(pitchInHz >= 110 && pitchInHz < 123.47) {
        //A
        noteText.setText("A");
    }
    else if(pitchInHz >= 123.47 && pitchInHz < 130.81) {
        //B
        noteText.setText("B");
    }
    else if(pitchInHz >= 130.81 && pitchInHz < 146.83) {
        //C
        noteText.setText("C");
    }
    else if(pitchInHz >= 146.83 && pitchInHz < 164.81) {
        //D
        noteText.setText("D");
    }
    else if(pitchInHz >= 164.81 && pitchInHz <= 174.61) {
        //E
        noteText.setText("E");
    }
    else if(pitchInHz >= 174.61 && pitchInHz < 185) {
        //F
        noteText.setText("F");
    }
    else if(pitchInHz >= 185 && pitchInHz < 196) {
        //G
        noteText.setText("G");
    }
}

错误代码：

03-05 15:12:38.297 7642-7642/com.example.richard.jtransformtest E/AndroidRuntime: FATAL EXCEPTION: main
                                                                              Process: com.example.richard.jtransformtest, PID: 7642
                                                                              java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
                                                                                  at com.example.richard.jtransformtest.MainActivity.processPitch(MainActivity.java:62)
                                                                                  at com.example.richard.jtransformtest.MainActivity$1$1.run(MainActivity.java:43)
                                                                                  at android.os.Handler.handleCallback(Handler.java:836)
                                                                                  at android.os.Handler.dispatchMessage(Handler.java:103)
                                                                                  at android.os.Looper.loop(Looper.java:203)
                                                                                  at android.app.ActivityThread.main(ActivityThread.java:6251)
                                                                                  at java.lang.reflect.Method.invoke(Native Method)
                                                                                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1063)
                                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:924)

最后是XML：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="16dp"
android:paddingRight="16dp"
android:orientation="vertical" >

<TextView
    android:id="@+id/pitchText"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="TextView" />

<TextView
    android:id="@+id/noteText"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="TextView" />
</LinearLayout>

任何帮助都会非常受欢迎。

对不起......我真的很蠢，并没有注意到有重复..谢谢大家的答案

Answer 1

你的noteText是null，因为你只是忘了在你的findViewById noteText做正确的TextView检查它

用这个

pitchText = (TextView) findViewById(R.id.pitchText);
noteText = (TextView) findViewById(R.id.noteText);

而不是这个

pitchText = (TextView) findViewById(R.id.pitchText);
pitchText = (TextView) findViewById(R.id.noteText);

Answer 2

pitchText = (TextView) findViewById(R.id.pitchText);
pitchText = (TextView) findViewById(R.id.noteText);

你的noteText是空的，因为你没有分配它。

Answer 3

你必须改变这个：

 pitchText = (TextView) findViewById(R.id.pitchText);
 pitchText = (TextView) findViewById(R.id.noteText);

如下：

 pitchText = (TextView) findViewById(R.id.pitchText);
 noteText= (TextView) findViewById(R.id.noteText);