我试图添加一个按钮，并在点击时切换布局，但每次我运行应用程序时;它意外停止了。我很困惑，如果有人可以帮助我那将是非常棒的。
Logcat消息 -
01-02 18:41:54.844: W/dalvikvm(2070): threadid=1: thread exiting with uncaught exception (group=0xb0f00648)
01-02 18:41:54.844: E/AndroidRuntime(2070): FATAL EXCEPTION: main
01-02 18:41:54.844: E/AndroidRuntime(2070): java.lang.NullPointerException
01-02 18:41:54.844: E/AndroidRuntime(2070): at sehej.android.doge.FullscreenActivity$3.onVisibilityChange(FullscreenActivity.java:82)
01-02 18:41:54.844: E/AndroidRuntime(2070): at sehej.android.doge.util.SystemUiHiderHoneycomb$1.onSystemUiVisibilityChange(SystemUiHiderHoneycomb.java:113)
FullScreenActivity.java（主屏幕的Java文件） -
public class FullscreenActivity extends Activity {
private static final boolean AUTO_HIDE = true;
private static final int AUTO_HIDE_DELAY_MILLIS = 3000;
private static final boolean TOGGLE_ON_CLICK = true;
private static final int HIDER_FLAGS = SystemUiHider.FLAG_HIDE_NAVIGATION;
private SystemUiHider mSystemUiHider;
public void button1_click(final View view)
{
startActivity(new Intent(this, MainGameActivity.class));
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final View controlsView = findViewById(R.id.fullscreen_content_controls);
final View contentView = findViewById(R.id.fullscreen_content);
mSystemUiHider = SystemUiHider.getInstance(this, contentView,
HIDER_FLAGS);
mSystemUiHider.setup();
mSystemUiHider
.setOnVisibilityChangeListener(new SystemUiHider.OnVisibilityChangeListener() {
// Cached values.
int mControlsHeight;
int mShortAnimTime;
@Override
@TargetApi(Build.VERSION_CODES.HONEYCOMB_MR2)
public void onVisibilityChange(boolean visible) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB_MR2) {
if (mControlsHeight == 0) {
mControlsHeight = controlsView.getHeight();
}
if (mShortAnimTime == 0) {
mShortAnimTime = getResources().getInteger(
android.R.integer.config_shortAnimTime);
}
controlsView
.animate()
.translationY(visible ? 0 : mControlsHeight)
.setDuration(mShortAnimTime);
} else {
controlsView.setVisibility(visible ? View.VISIBLE
: View.GONE);
}
if (visible && AUTO_HIDE) { delayedHide(AUTO_HIDE_DELAY_MILLIS);
}
}
});
// Set up the user interaction to manually show or hide the system UI.
contentView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (TOGGLE_ON_CLICK) {
mSystemUiHider.toggle();
} else {
mSystemUiHider.show();
}
}
});
};
@Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
delayedHide(100);
}
View.OnTouchListener mDelayHideTouchListener = new View.OnTouchListener() {
@Override
public boolean onTouch(View view, MotionEvent motionEvent) {
if (AUTO_HIDE) {
delayedHide(AUTO_HIDE_DELAY_MILLIS);
}
return false;
}
};
Handler mHideHandler = new Handler();
Runnable mHideRunnable = new Runnable() {
@Override
public void run() {
mSystemUiHider.hide();
}
};
private void delayedHide(int delayMillis) {
mHideHandler.removeCallbacks(mHideRunnable);
mHideHandler.postDelayed(mHideRunnable, delayMillis);
}
}
activity_main.xml（主屏幕的布局） -
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/grass"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
app:padding="20sp"
app:textAlignment="center"
tools:context=".MainActivity" >
<View
app:id="@+id/fullscreen_content_controls"
app:layout_width="wrap_content"
app:layout_height="wrap_content" />
<View
app:id="@+id/fullscreen_content"
app:layout_width="wrap_content"
app:layout_height="wrap_content" />
<requestFocus
app:layout_width="wrap_content"
app:layout_height="wrap_content" />
<Button
app:id="@+id/button1"
style="@style/ButtonBar"
app:layout_width="150dp"
app:layout_height="wrap_content"
app:layout_below="@+id/textView1"
app:layout_centerHorizontal="true"
app:layout_marginTop="45dp"
app:onClick="button1_click"
app:text="@string/button1"
app:typeface="sans" />
<TextView
app:id="@+id/textView1"
app:layout_width="wrap_content"
app:layout_height="wrap_content"
app:layout_alignParentTop="true"
app:layout_centerHorizontal="true"
app:layout_marginTop="14dp"
app:text="@string/title"
app:textColor="@color/blue"
app:textSize="60sp"
app:textStyle="bold"
app:typeface="sans" />
<Button
app:id="@+id/button2"
style="@style/ButtonBar"
app:layout_width="150dp"
app:layout_height="wrap_content"
app:layout_alignLeft="@+id/button1"
app:layout_below="@+id/button1"
app:layout_marginTop="52dp"
app:text="@string/button2"
app:typeface="sans" />
<ImageButton
app:id="@+id/imageButton1"
style="@style/FullscreenActionBarStyle"
app:layout_width="wrap_content"
app:layout_height="wrap_content"
app:layout_alignParentBottom="true"
app:layout_alignRight="@+id/textView1"
app:contentDescription="@string/dogepic_info"
app:src="@drawable/doge" />
<TextView
app:id="@+id/textView2"
app:layout_width="wrap_content"
app:layout_height="wrap_content"
app:layout_alignTop="@+id/imageButton1"
app:layout_centerHorizontal="true"
app:text="@string/dogepic_caption"
app:textColor="@color/green"
app:textSize="15sp"
app:textStyle="bold"
app:typeface="sans" />
</RelativeLayout>
答案 0 :(得分：0)
此方法应在onCreate（）中注册为onClickListener。此外，它的View参数不能是最终的。
public void button1_click(final View view)
{
startActivity(new Intent(this, MainGameActivity.class));
}
换句话说，你应该写：
public class FullscreenActivity extends Activity {
private static final boolean AUTO_HIDE = true;
private static final int AUTO_HIDE_DELAY_MILLIS = 3000;
private static final boolean TOGGLE_ON_CLICK = true;
private static final int HIDER_FLAGS = SystemUiHider.FLAG_HIDE_NAVIGATION;
private SystemUiHider mSystemUiHider;
Button buttonView;
View controlsView;
View contentView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
contentView = (View)findViewById(R.id.fullscreen_content);
controlsView = (View)findViewById(R.id.fullscreen_content_controls);
buttonView = (View)findViewById(R.id.button1);
buttonView.setOnClickListener(myButtonHandler);
mSystemUiHider = SystemUiHider.getInstance(this, contentView,
HIDER_FLAGS);
mSystemUiHider.setup();
mSystemUiHider
.setOnVisibilityChangeListener(new SystemUiHider.OnVisibilityChangeListener() {
int mControlsHeight;
int mShortAnimTime;
}
View.OnClickListener myButtonHandler = new View.OnClickListener() {
public void onClick(View v) {
startActivity(new Intent(this, MainGameActivity.class));
}
};
@Override
@TargetApi(Build.VERSION_CODES.HONEYCOMB_MR2)
public void onVisibilityChange(boolean visible) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB_MR2) {
if (mControlsHeight == 0) {
mControlsHeight = controlsView.getHeight();
}
if (mShortAnimTime == 0) {
mShortAnimTime = getResources().getInteger(
android.R.integer.config_shortAnimTime);
}
controlsView
.animate()
.translationY(visible ? 0 : mControlsHeight)
.setDuration(mShortAnimTime);
} else {
controlsView.setVisibility(visible ? View.VISIBLE
: View.GONE);
}
if (visible && AUTO_HIDE) {
delayedHide(AUTO_HIDE_DELAY_MILLIS);
}
}
});
contentView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (TOGGLE_ON_CLICK) {
mSystemUiHider.toggle();
} else {
mSystemUiHider.show();
}
}
});
};
答案 1 :(得分：0)
是的，你声明事物的方式不是最好的做法，你得到一个空指针异常，这意味着没有找到，初始化，声明或不存在引用，变量等..希望帮助
答案 2 :(得分：0)
堆栈跟踪为您提供跟踪错误所需的所有信息。在顶部，两行告诉您，您尝试通过空引用访问变量或方法：
java.lang.NullPointerException
at sehej.android.doge.FullscreenActivity$3.onVisibilityChange(FullscreenActivity.java:82)
当只需要第82行周围的区域时，您已经为我们粘贴了此源文件的内容以及更多文件。当然，堆栈跟踪告诉你这一点，所以学会阅读它 - 它是一个非常宝贵的调试工具。
为了帮助您入门，以下是第81-83行：
if (mControlsHeight == 0) {
mControlsHeight = controlsView.getHeight();
}
在程序的第36行，您尝试实例化 controlsView ，如下所示：
final View controlsView = findViewById(R.id.fullscreen_content_controls);
在此行之后添加一个调试语句，打印 controlsView 变量。它是否产生对象引用或“（null）”？如果它为null，为什么你认为 findViewById（）可能会失败？