对 Android 来说非常新，现在已经研究了一段时间，但找不到答案。我确信有一个简单的解决方案。
我得到一个NullPointException连接到我的View characterContainer = findViewById(R.id.icon_container);
据我了解，似乎我正在尝试在该onCreate()方法中实现它，因此布局尚未完全准备好导致characterContainer = null.
所以我需要使用它，onStart()或者onResume()但我正在努力。到目前为止，这是我的代码：
package harvest.life.game;
import android.app.Activity;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.RelativeLayout;
public class HarvestLifeActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//find buttons on screen
Button up = (Button)findViewById(R.id.up);
up.setOnTouchListener(new UpListener());
Button down = (Button)findViewById(R.id.down);
down.setOnTouchListener(new UpListener()); // set as UpListener also for test reasons
Button left = (Button)findViewById(R.id.left);
left.setOnTouchListener(new UpListener()); // set as UpListener also for test reasons
Button right = (Button)findViewById(R.id.right);
right.setOnTouchListener(new UpListener()); // set as UpListener also for test reasons
}
//what up button does
private final class UpListener implements OnTouchListener {
public boolean onTouch(View v, MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
//as long as up button is pressed it will keep moving character up
while (event.getAction() == MotionEvent.ACTION_DOWN)
{
View characterContainer = findViewById(R.id.icon_container);
Drawable walking = getResources().getDrawable(R.drawable.test_circle_red);
int startX = characterContainer.getLeft();
int startY = characterContainer.getTop();
int defaultWidth = characterContainer.getWidth();
int defaultHeight = characterContainer.getHeight();
//create new position for character 1 pixel closer to the top of screen
int newX = startX - 1;
int newY = startY;
//remove character
RelativeLayout view = (RelativeLayout) characterContainer;
ViewGroup owner = (ViewGroup) view.getParent();
owner.removeView(view);
//re make character in new position created above and assign background as walking forwards animation
RelativeLayout.LayoutParams characParams = new RelativeLayout.LayoutParams(defaultWidth,defaultHeight);
characParams.leftMargin = newY;
characParams.topMargin = newX;
characterContainer.setLayoutParams(characParams);
characterContainer.setBackgroundDrawable(walking);
}
break;
// when button is let go of
case MotionEvent.ACTION_UP:
RelativeLayout characterContainer = (RelativeLayout)
findViewById(R.id.icon_container);
Drawable standing =
getResources().getDrawable(R.drawable.test_circle);
//assign background back to standing animation
characterContainer.setBackgroundDrawable(standing);
default:
break;
}
return true;
}
}
public void onResume() { // what goes here?
}
}
我是否需要在该部分中放置一种函数调用，onResume或者我是否将代码OnTouchListener放在此处？
这是我的主要内容：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/game_container"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal"
android:background="#FFFFFF">
<RelativeLayout
android:id="@+id/side_bar_right"
android:layout_width="50dp"
android:layout_height="fill_parent"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true"
android:background="#000000">
<ImageView
android:contentDescription="@string/movement_button"
android:id="@+id/up"
android:layout_width="50dp"
android:layout_height="50dp"
android:layout_gravity="top"
android:src="@drawable/up" />
<ImageView
android:contentDescription="@string/movement_button"
android:id="@+id/down"
android:layout_width="50dp"
android:layout_height="50dp"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:src="@drawable/down" />
<ImageView
android:contentDescription="@string/movement_button"
android:id="@+id/right"
android:layout_width="50dp"
android:layout_height="50dp"
android:layout_alignParentLeft="true"
android:layout_centerVertical="true"
android:src="@drawable/right" />
</RelativeLayout>
<RelativeLayout
android:id="@+id/side_bar_left"
android:layout_width="50dp"
android:layout_height="fill_parent"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:background="#000000">
<ImageView
android:contentDescription="@string/movement_button"
android:id="@+id/left"
android:layout_width="50dp"
android:layout_height="50dp"
android:layout_alignParentLeft="true"
android:layout_centerVertical="true"
android:src="@drawable/left" />
</RelativeLayout>
<RelativeLayout
android:id="@+id/icon_container"
android:layout_width="50dp"
android:layout_height="50dp"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:background="@drawable/test_circle" >
</RelativeLayout >
</RelativeLayout>