Question

我使用了我对谷歌here发布的文档的理解编辑：我用其中的动画制作了第二个.xml（称为shake_animation）并更新了主java类中的引用

我认为他们的问题现在可能在主java类中，也许在图像视图和frameAnimation之间发生了某种冲突？

package shake.shake;

/**
 * Created by ink on 3/24/16.
 */
import android.app.Activity;
import android.content.Context;
import android.graphics.drawable.AnimationDrawable;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;

public class main extends Activity implements SensorEventListener {
    private float mLastX, mLastY, mLastZ;
    private boolean mInitialized;
    private SensorManager mSensorManager;
    private Sensor mAccelerometer;

    private final float NOISE = (float) 4.0;


    /**
     * Called when the activity is first created.
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        mInitialized = false;
        mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
        mAccelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
        mSensorManager.registerListener(this, mAccelerometer, SensorManager.SENSOR_DELAY_NORMAL);
    }
    protected void onResume() {
        super.onResume();
        mSensorManager.registerListener(this, mAccelerometer, SensorManager.SENSOR_DELAY_NORMAL);
    }

    protected void onPause() {
        super.onPause();
        mSensorManager.unregisterListener(this);
    }

    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {
// can be safely ignored for this demo
    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        // Load the ImageView that will host the animation and
        // set its background to our AnimationDrawable XML resource.
        ImageView img = (ImageView)findViewById(R.id.shake1);
        img.setBackgroundResource(R.drawable.shake_animation);

        // Get the background, which has been compiled to an AnimationDrawable object.
        AnimationDrawable frameAnimation = (AnimationDrawable) img.getBackground();

        // Start the animation (looped playback by default).
        frameAnimation.start();

        TextView tvX= (TextView)findViewById(R.id.x_axis);
        TextView tvY= (TextView)findViewById(R.id.calories);
        TextView tvZ= (TextView)findViewById(R.id.z_axis);
        float x = event.values[0];
        float y = event.values[1];
        float z = event.values[2];
        if (!mInitialized) {
            mLastX = x;
            mLastY = y;
            mLastZ = z;
            tvX.setText("0.0");
            tvY.setText("0.0");
            tvZ.setText("0.0");
            mInitialized = true;
        } else {
            float deltaX = Math.abs(mLastX - x);
            float deltaY = Math.abs(mLastY - y);
            float deltaZ = Math.abs(mLastZ - z);
            if (deltaX < NOISE) deltaX = (float)0.0;
            if (deltaY < NOISE) deltaY = (float)0.0;
            if (deltaZ < NOISE) deltaZ = (float)0.0;
            mLastX = x;
            mLastY = y;
            mLastZ = z;
            tvX.setText(Float.toString(deltaX));
            tvY.setText(Float.toString(deltaY));
            tvZ.setText(Float.toString(deltaZ));
            if (deltaX > deltaY) {
                frameAnimation.start();
            } else if (deltaY > deltaX) {
                frameAnimation.start();
            } else {
                frameAnimation.stop();
            }
        }
    }
    }

这是我的xml文件，我想这可能就是问题出在哪里了，但谷歌推出的页面并没有对这里放置什么有如此好的描述

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">

    <ImageView
        android:id="@+id/shake1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:background="@drawable/shake1" />

    <item
        android:duration="50"
        android:drawable="@drawable/shake1"/>

    <item
        android:duration="50"
        android:drawable="@drawable/shake1"/>
     <item
        android:duration="50"
        android:drawable="@drawable/shake2"/>

    <item
        android:duration="50"
        android:drawable="@drawable/shake3"/>

    <item
        android:duration="50"
        android:drawable="@drawable/shake4"/>
</selector>

这是logcat（更新）：

04-12 01:18:57.824 2081-2081/shake.shake E/AndroidRuntime: FATAL EXCEPTION: main
                                                           Process: shake.shake, PID: 2081
                                                           java.lang.ClassCastException: android.graphics.drawable.StateListDrawable cannot be cast to android.graphics.drawable.AnimationDrawable
                                                               at shake.shake.main.onSensorChanged(main.java:62)
                                                               at android.hardware.SystemSensorManager$SensorEventQueue.dispatchSensorEvent(SystemSensorManager.java:481)
                                                               at android.os.MessageQueue.nativePollOnce(Native Method)
                                                               at android.os.MessageQueue.next(MessageQueue.java:323)
                                                               at android.os.Looper.loop(Looper.java:135)
                                                               at android.app.ActivityThread.main(ActivityThread.java:5422)
                                                               at java.lang.reflect.Method.invoke(Native Method)
                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

这是可绘制列表.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <animation-list android:id="@+id/shake_animation" android:oneshot="false">
        <item android:drawable="@drawable/shake1" android:duration="50" />
        <item android:drawable="@drawable/shake2" android:duration="50" />
        <item android:drawable="@drawable/shake3" android:duration="50" />
        <item android:drawable="@drawable/shake4" android:duration="50" />
    </animation-list>
    <image
        android:id="@+id/shake1"
        android:src="@drawable/shake1"
        />
</selector>

Answer 1

将动画与布局代码分开非常重要。

将动画列表放在drawable文件夹中名为anime.xml的xml文件中，如下所示

<?xml version="1.0" encoding="utf-8"?>
<animation-list xmlns:android="http://schemas.android.com/apk/res/android"
android:oneshot="true">
    <item android:drawable="@drawable/shake1" android:duration="50" />
    <item android:drawable="@drawable/shake2" android:duration="50" />
    <item android:drawable="@drawable/shake3" android:duration="50" />
    <item android:drawable="@drawable/shake4" android:duration="50" />
</animation-list>

让你的java代码使用以下

    ImageView img = (ImageView) findViewById(R.id.shake1);
    img.setBackgroundResource(R.drawable.anime);
    AnimationDrawable frameAnimation = (AnimationDrawable) img.getBackground();

Answer 2

您收到此错误：

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setBackgroundResource(int)' on a null object reference

这意味着您没有初始化ImageView或者您传递的参数setBackgroundResource(int)为空。粘贴活动代码以获得更多错误清除。

启动/停止传感器事件

2 个答案: