package com.example.first666;
import com.example.first666.util.SystemUiHider;
import android.annotation.TargetApi;
import android.app.Activity;
import android.os.Build;
import android.os.Bundle;
import android.os.Handler;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
/**
* An example full-screen activity that shows and hides the system UI (i.e.
* status bar and navigation/system bar) with user interaction.
*
* @see SystemUiHider
*/
public class FullscreenActivity extends Activity {
int counter;
Button add, sub;
TextView display;
/**
* Whether or not the system UI should be auto-hidden after
* {@link #AUTO_HIDE_DELAY_MILLIS} milliseconds.
*/
private static final boolean AUTO_HIDE = true;
/**
* If {@link #AUTO_HIDE} is set, the number of milliseconds to wait after
* user interaction before hiding the system UI.
*/
private static final int AUTO_HIDE_DELAY_MILLIS = 3000;
/**
* If set, will toggle the system UI visibility upon interaction. Otherwise,
* will show the system UI visibility upon interaction.
*/
private static final boolean TOGGLE_ON_CLICK = true;
/**
* The flags to pass to {@link SystemUiHider#getInstance}.
*/
private static final int HIDER_FLAGS = SystemUiHider.FLAG_HIDE_NAVIGATION;
/**
* The instance of the {@link SystemUiHider} for this activity.
*/
private SystemUiHider mSystemUiHider;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_fullscreen);
counter = 0;
add = (Button) findViewById(R.id.bAdd);
sub = (Button) findViewById(R.id.bSub);
display = (TextView) findViewById(R.id.tvDisplay);
add.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
counter++;
display.setText("Your total is " + counter);
}
});
sub.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
counter--;
display.setText("Your total is " + counter);
}
});
final View controlsView = findViewById(R.id.fullscreen_content_controls);
final View contentView = findViewById(R.id.fullscreen_content);
// Set up an instance of SystemUiHider to control the system UI for
// this activity.
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 the ViewPropertyAnimator API is available
// (Honeycomb MR2 and later), use it to animate the
// in-layout UI controls at the bottom of the
// screen.
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 {
// If the ViewPropertyAnimator APIs aren't
// available, simply show or hide the in-layout UI
// controls.
controlsView.setVisibility(visible ? View.VISIBLE
: View.GONE);
}
if (visible && AUTO_HIDE) {
// Schedule a 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();
}
}
});
// Upon interacting with UI controls, delay any scheduled hide()
// operations to prevent the jarring behavior of controls going away
// while interacting with the UI.
findViewById(R.id.dummy_button).setOnTouchListener(
mDelayHideTouchListener);
}
@Override
public void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
// Trigger the initial hide() shortly after the activity has been
// created, to briefly hint to the user that UI controls
// are available.
delayedHide(100);
}
/**
* Touch listener to use for in-layout UI controls to delay hiding the
* system UI. This is to prevent the jarring behavior of controls going away
* while interacting with activity UI.
*/
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();
}
};
/**
* Schedules a call to hide() in [delay] milliseconds, canceling any
* previously scheduled calls.
*/
public void delayedHide(int delayMillis) {
mHideHandler.removeCallbacks(mHideRunnable);
mHideHandler.postDelayed(mHideRunnable, delayMillis);
}
}
当display = (TextView) findViewById(R.id.tvDisplay);应用程序崩溃说“不幸的是应用程序已停止”时，会发生 nullpointerexception。如何修复 NullPointerException？
这是所要求的 XML 文件。任何帮助表示赞赏。
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:id="@+id/tvDisplay"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hello"
android:textSize="200sp"
android:layout_gravity="center"
android:gravity="center"/>
<Button
android:layout_width="500sp"
android:layout_height="200sp"
android:text="@string/Add"
android:layout_gravity="center"
android:gravity="center"
android:textSize="75sp"
android:id="@+id/bAdd"/>
<Button
android:layout_width="500sp"
android:layout_height="200sp"
android:text="@string/Sub"
android:layout_gravity="center"
android:textSize="75sp"
android:id="@+id/bSub"/>
</LinearLayout>
这是所要求的 LogCat
06-05 14:52:46.269: E/Trace(466): error opening trace file: No such file or directory (2)
06-05 14:52:48.300: D/AndroidRuntime(466): Shutting down VM
06-05 14:52:48.309: W/dalvikvm(466): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
06-05 14:52:48.360: E/AndroidRuntime(466): FATAL EXCEPTION: main
06-05 14:52:48.360: E/AndroidRuntime(466): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.first666/com.example.first666.FullscreenActivity}: java.lang.NullPointerException
06-05 14:52:48.360: E/AndroidRuntime(466): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
06-05 14:52:48.360: E/AndroidRuntime(466): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
06-05 14:52:48.360: E/AndroidRuntime(466): at android.app.ActivityThread.access$600(ActivityThread.java:141)
06-05 14:52:48.360: E/AndroidRuntime(466): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
06-05 14:52:48.360: E/AndroidRuntime(466): at android.os.Handler.dispatchMessage(Handler.java:99)
06-05 14:52:48.360: E/AndroidRuntime(466): at android.os.Looper.loop(Looper.java:137)
06-05 14:52:48.360: E/AndroidRuntime(466): at android.app.ActivityThread.main(ActivityThread.java:5041)
06-05 14:52:48.360: E/AndroidRuntime(466): at java.lang.reflect.Method.invokeNative(Native Method)
06-05 14:52:48.360: E/AndroidRuntime(466): at java.lang.reflect.Method.invoke(Method.java:511)
06-05 14:52:48.360: E/AndroidRuntime(466): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
06-05 14:52:48.360: E/AndroidRuntime(466): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
06-05 14:52:48.360: E/AndroidRuntime(466): at dalvik.system.NativeStart.main(Native Method)
06-05 14:52:48.360: E/AndroidRuntime(466): Caused by: java.lang.NullPointerException
06-05 14:52:48.360: E/AndroidRuntime(466): at com.example.first666.FullscreenActivity.onCreate(FullscreenActivity.java:62)
06-05 14:52:48.360: E/AndroidRuntime(466): at android.app.Activity.performCreate(Activity.java:5104)
06-05 14:52:48.360: E/AndroidRuntime(466): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
06-05 14:52:48.360: E/AndroidRuntime(466): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
06-05 14:52:48.360: E/AndroidRuntime(466): ... 11 more
06-05 14:53:28.219: I/Process(466): Sending signal. PID: 466 SIG: 9