我正在我的代码中实现滑动操作来更改背景图像。但是,当我运行我的应用程序崩溃。我不知道我的代码中有什么不对。
代码 -
public class Types extends Activity{
RelativeLayout layout1;
int[] backgroundResId;
int currentIndex=0;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_type);
backgroundResId=new int[]{R.drawable.back,R.drawable.bg,R.drawable.frame1};
changeBackground();
ActivitySwipeDetector activitySwipeDetector = new ActivitySwipeDetector(this);
layout1.setOnTouchListener(activitySwipeDetector);
}
private void changeBackground(){
findViewById(R.id.layout1).setBackgroundResource(backgroundResId[currentIndex]);
}
public class ActivitySwipeDetector implements View.OnTouchListener {
static final String logTag = "ActivitySwipeDetector";
static final int MIN_DISTANCE = 100;
private float downX, upX;
private Activity activity;
public ActivitySwipeDetector(Activity activity){
this.activity = activity;
}
public void onRightToLeftSwipe(){
Log.i(logTag, "RightToLeftSwipe!");
currentIndex++;
if(currentIndex<backgroundResId.length){
changeBackground();
}
}
public void onLeftToRightSwipe(){
Log.i(logTag, "LeftToRightSwipe!");
if(currentIndex>0){
changeBackground();
}
}
public boolean onTouch(View v, MotionEvent event) {
switch(event.getAction()){
case MotionEvent.ACTION_DOWN: {
downX = event.getX();
return true;
}
case MotionEvent.ACTION_UP: {
upX = event.getX();
float deltaX = downX - upX;
// swipe horizontal?
if(Math.abs(deltaX) > MIN_DISTANCE){
// left or right
if(deltaX < 0) { this.onLeftToRightSwipe(); return true; }
if(deltaX > 0) { this.onRightToLeftSwipe(); return true; }
}
else {
Log.i(logTag, "Swipe was only " + Math.abs(deltaX) + " long, need at least " + MIN_DISTANCE);
return false; // We don't consume the event
}
return true;
}
}
return false;
}
}
}
答案 0 :(得分:3)
RelativeLayout layout1;
您已声明但未初始化layout1,请使用id初始化它并尝试。
答案 1 :(得分:0)
您必须获取NullPointerException,因为您尚未初始化RelativeLayout实例 layout1 。这样做 -
private void changeBackground()
{
layout1 = findViewById(R.id.layout1);
layout1.setBackgroundResource(backgroundResId[currentIndex]);
}