这是我的代码
public class MainActivity extends Activity {
// Used to load the 'native-lib' library on application startup.
static {
System.loadLibrary("native-lib");
}
private ViewPager viewPager;
private ViewPagerAdapter viewPagerAdapter;
private static android.widget.EditText favcolor;
private TextView textout;
private LinearLayout dotsLayout;
private TextView[] dots;
private int[] layouts;
private Button btnSkip, btnNext;
@Override
protected void onCreate(Bundle savedInstanceState) {
requestWindowFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
viewPager = (ViewPager) findViewById(R.id.view_pager);
dotsLayout = (LinearLayout) findViewById(R.id.layoutDots);
btnNext = (Button) findViewById(R.id.btn_next);
layouts = new int[]{
R.layout.slide1,
R.layout.slide2,
R.layout.slide3};
// adding bottom dots
addBottomDots(0);
viewPagerAdapter = new ViewPagerAdapter();
viewPager.setAdapter(viewPagerAdapter);
viewPager.addOnPageChangeListener(viewPagerPageChangeListener);
}
public void btnNextClick(View v)
{
// checking for last page
// if last page home screen will be launched
int current = getItem(1);
if (current < layouts.length) {
// move to next screen
viewPager.setCurrentItem(current);
} else {
launchHomeScreen();
}
}
ViewPager.OnPageChangeListener viewPagerPageChangeListener = new ViewPager.OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
addBottomDots(position);
// changing the next button text 'NEXT' / 'GOT IT'
if (position == layouts.length - 1) {
// last page. make button text to GOT IT
favcolor = (android.widget.EditText) findViewById(R.id.text);
textout = (TextView) findViewById(R.id.txtOutput);
textout.setText(favcolor.getText());
btnNext.setText(getString(R.string.start));
btnSkip.setVisibility(View.GONE);
} else {
// still pages are left
btnNext.setText(getString(R.string.next));
btnSkip.setVisibility(View.VISIBLE);
}
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
}
@Override
public void onPageScrollStateChanged(int arg0) {
}
};
private void addBottomDots(int currentPage) {
dots = new TextView[layouts.length];
dotsLayout.removeAllViews();
for (int i = 0; i < dots.length; i++) {
dots[i] = new TextView(this);
dots[i].setText(Html.fromHtml("•"));
dots[i].setTextSize(35);
dots[i].setTextColor(getResources().getColor(R.color.dot_inactive));
dotsLayout.addView(dots[i]);
}
if (dots.length > 0)
dots[currentPage].setTextColor(getResources().getColor(R.color.dot_active));
}
private int getItem(int i) {
return viewPager.getCurrentItem() + i;
}
private void launchHomeScreen() {
startActivity(new Intent(this, MainActivity.class));
finish();
}
public class ViewPagerAdapter extends PagerAdapter {
private LayoutInflater layoutInflater;
public ViewPagerAdapter() {
}
@Override
public Object instantiateItem(ViewGroup container, int position) {
layoutInflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View view = layoutInflater.inflate(layouts[position], container, false);
container.addView(view);
return view;
}
@Override
public int getCount() {
return layouts.length;
}
@Override
public boolean isViewFromObject(View view, Object obj) {
return view == obj;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
View view = (View) object;
container.removeView(view);
}
/**
* A native method that is implemented by the 'native-lib' native library,
* which is packaged with this application.
*/
public native String stringFromJNI();
}
}
这就是错误
01-28 12:30:06.827 26862-26862/com.example.jorgesalgado.singular20 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.jorgesalgado.singular20, PID: 26862
java.lang.IllegalStateException: Could not execute method for android:onClick
at android.view.View$DeclaredOnClickListener.onClick(View.java:4725)
at android.view.View.performClick(View.java:5637)
at android.view.View$PerformClick.run(View.java:22429)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at android.view.View$DeclaredOnClickListener.onClick(View.java:4720)
at android.view.View.performClick(View.java:5637)
at android.view.View$PerformClick.run(View.java:22429)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setVisibility(int)' on a null object reference
at com.example.jorgesalgado.singular20.MainActivity$1.onPageSelected(MainActivity.java:103)
at android.support.v4.view.ViewPager.dispatchOnPageSelected(ViewPager.java:1967)
at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:685)
at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:669)
at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:630)
at android.support.v4.view.ViewPager.setCurrentItem(ViewPager.java:611)
at com.example.jorgesalgado.singular20.MainActivity.btnNextClick(MainActivity.java:80)
at java.lang.reflect.Method.invoke(Native Method)
at android.view.View$DeclaredOnClickListener.onClick(View.java:4720)
at android.view.View.performClick(View.java:5637)
at android.view.View$PerformClick.run(View.java:22429)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at ) com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776
我很确定它与Next按钮有关，但我不确定。请帮帮我。我14岁，我只使用javascript，css，python和html。我假设这是java，这很难学。但是我开始把基础知识搞定了。
答案 0 :(得分：1)
您永远不会初始化btnSkip。所以它是null。
执行btnSkip.setVisibility()后，您会收到例外Attempt to invoke virtual method 'void android.view.View.setVisibility(int)' on a null object reference，因为btnSkip为null。
错误消息字面上指向错误的位置 - MainActivity.java第103行