我正在制作一个程序,在摇动手机或按下按钮时会显示随机文本。我是新手,所以我导入了很多代码并尝试理解然后进行修改。
我可以肯定它是if (speed > SHAKE_THRESHOLD)
中的正文,因为当它为空时它可以工作,但不会更改文本视图。
我的日志猫:
07-19 14:10:24.131 5671-5708/com.example.user.something E/Surface: getSlotFromBufferLocked: unknown buffer: 0xae64c640 07-19 14:10:33.019 5671-5671/com.example.user.something E/SensorManager: Exception dispatching input event. 07-19 14:10:33.019 5671-5671/com.example.user.something E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.user.something, PID: 5671 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference at com.example.user.something.Main2Activity.onSensorChanged(Main2Activity.java:103) at android.hardware.SystemSensorManager$SensorEventQueue.dispatchSensorEvent(SystemSensorManager.java:481) at android.os.MessageQueue.nativePollOnce(Native Method) at android.os.MessageQueue.next(MessageQueue.java:323) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5417) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
我的代码是:
package com.example.user.something;
import android.content.Context;
import android.content.Intent;
import android.content.res.Resources;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.net.Uri;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.util.Random;
public class Main2Activity extends AppCompatActivity implements SensorEventListener {
public SensorManager senSensorManager;
public Sensor senAccelerometer;
private long lastUpdate = 0;
public float last_x, last_y, last_z;
private static final int SHAKE_THRESHOLD = 600;
public Button b2;
public String[] songs, links;
public Button b3;
public String q;
public String q1;
public TextView tv;
public static final Random rgenerator = new Random();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
senSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
senAccelerometer = senSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
senSensorManager.registerListener(this, senAccelerometer, SensorManager.SENSOR_DELAY_NORMAL);
b2 = (Button) findViewById(R.id.button2);
b3 = (Button) findViewById(R.id.button3);
final TextView tv = (TextView) findViewById(R.id.text1);
final Resources res = getResources();
links = res.getStringArray(R.array.links);
songs = res.getStringArray(R.array.songs);
tv.setText("My Awesome Text");
b2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
String q = songs[rgenerator.nextInt(songs.length)];
String q1 = links[rgenerator.nextInt(songs.length)];
tv.setText(q);
}
});
b3.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent browserIntent = new Intent(
Intent.ACTION_VIEW,
Uri.parse(q));
startActivity(browserIntent);
}
});
}
@Override
public void onSensorChanged(SensorEvent sensorEvent) {
Sensor mySensor = sensorEvent.sensor;
if (mySensor.getType() == Sensor.TYPE_ACCELEROMETER) {
float x = sensorEvent.values[0];
float y = sensorEvent.values[1];
float z = sensorEvent.values[2];
long curTime = System.currentTimeMillis();
if ((curTime - lastUpdate) > 100) {
long diffTime = (curTime - lastUpdate);
lastUpdate = curTime;
float speed = Math.abs(x + y + z - last_x - last_y - last_z) / diffTime * 10000;
if (speed > SHAKE_THRESHOLD) {
String q = songs[rgenerator.nextInt(songs.length)];
String q1 = links[rgenerator.nextInt(songs.length)];
tv.setText(q);
}
last_x = x;
last_y = y;
last_z = z;
}
}
}
@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {}
protected void onPause() {
super.onPause();
senSensorManager.unregisterListener(this);
}
protected void onResume() {
super.onResume();
senSensorManager.registerListener(this, senAccelerometer, SensorManager.SENSOR_DELAY_NORMAL);
}
}
答案 0 :(得分:1)
您有2个名为tv
的变量:一个从未初始化的实例变量和onCreate中已初始化的局部变量。不幸的是,在onSensorChanged
中,您使用了从未初始化过的那个,因此使用了NullPointerException。