java - 每当执行应用程序时，它在 android 模拟器中显示为空白

Question

下面我粘贴了应用程序的 java、xml 和 logcat 的副本。

这是我的java代码

---

package my.example.myproject;

import my.example.myproject.util.SystemUiHider;

import android.annotation.TargetApi;
import android.app.Activity;
import android.content.Intent;
import android.os.Build;
import android.os.Bundle;
import android.os.Handler;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;

/**
 * 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 {
    /**
     * 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;
    Button iol,help,about;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_fullscreen);
        final View controlsView = findViewById(R.id.fullscreen_content_controls);
        iol = (Button)findViewById(R.id.iolCalculation);
        help = (Button)findViewById(R.id.sHelp);
        about = (Button)findViewById(R.id.sAbout);
        Thread iolthread=new Thread(){
            public void run(){
                try{
                    iol.setOnClickListener(new View.OnClickListener() {


                            @Override
                            public void onClick(View v) {
                                // TODO Auto-generated method stub
                                setContentView(R.layout.selection);
                            }
                    });
                    Intent iolIntent=new Intent(FullscreenActivity.this,Selection.class);
                    startActivity(iolIntent);
                }
                finally{
                    finish();
                }
            }
        };  
        iolthread.start();
        // Set up an instance of SystemUiHider to control the system UI for
        // this activity.
        mSystemUiHider = SystemUiHider.getInstance(this, controlsView,
                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.
        controlsView.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.

    }

    @Override
    protected 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.
     */
    private void delayedHide(int delayMillis) {
        mHideHandler.removeCallbacks(mHideRunnable);
        mHideHandler.postDelayed(mHideRunnable, delayMillis);
    }
}

---

XML

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/black"
    tools:context=".FullscreenActivity" 
    android:id="@+id/frame_layout">

        <LinearLayout
            android:id="@+id/fullscreen_content_controls"
            style="?buttonBarStyle"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="bottom|center_horizontal"
            android:background="@color/black_overlay"
            android:orientation="horizontal"
            tools:ignore="UselessParent" >
        </LinearLayout>

        <Button
            style="@style/ButtonBarButton"
            android:layout_width="222dp"
            android:layout_height="62dp"
            android:layout_marginLeft="45dp"
            android:layout_marginTop="75dp"
            android:background="@color/black"
            android:paddingLeft="20dp"
            android:id="@+id/iolCalculation"
            android:text="@string/Button"
            android:textColor="@color/WhiteSmoke"
            android:textStyle="bold" />

        <Button
            style="@style/ButtonBarButton"
            android:layout_width="222dp"
            android:layout_height="62dp"
            android:layout_marginLeft="45dp"
            android:id="@+id/sHelp"
            android:layout_marginTop="139dp"
            android:background="@color/Black"
            android:gravity="center"
            android:paddingLeft="10dp"
            android:text="@string/Button1"
            android:textColor="@color/WhiteSmoke"
            android:textStyle="bold" />

        <Button
            style="@style/ButtonBarButton"
            android:layout_width="222dp"
            android:layout_height="62dp"
            android:id="@+id/sAbout"
            android:layout_marginLeft="45dp"
            android:layout_marginTop="203dp"
            android:background="@color/Black"
            android:paddingLeft="10dp"
            android:text="@string/Button2"
            android:textColor="@color/WhiteSmoke"
            android:textStyle="bold" >

        </Button>
</FrameLayout>

---

日志

12-16 10:48:26.975: E/Trace(767): error opening trace file: No such file or directory (2)
12-16 10:51:38.199: E/AndroidRuntime(767): FATAL EXCEPTION: main
12-16 10:51:38.199: E/AndroidRuntime(767): java.lang.NullPointerException
12-16 10:51:38.199: E/AndroidRuntime(767):  at com.android.internal.widget.ActionBarView$3.onClick(ActionBarView.java:168)
12-16 10:51:38.199: E/AndroidRuntime(767):  at android.view.View.performClick(View.java:4202)
12-16 10:51:38.199: E/AndroidRuntime(767):  at android.view.View$PerformClick.run(View.java:17340)
12-16 10:51:38.199: E/AndroidRuntime(767):  at android.os.Handler.handleCallback(Handler.java:725)
12-16 10:51:38.199: E/AndroidRuntime(767):  at android.os.Handler.dispatchMessage(Handler.java:92)
12-16 10:51:38.199: E/AndroidRuntime(767):  at android.os.Looper.loop(Looper.java:137)
12-16 10:51:38.199: E/AndroidRuntime(767):  at android.app.ActivityThread.main(ActivityThread.java:5039)
12-16 10:51:38.199: E/AndroidRuntime(767):  at java.lang.reflect.Method.invokeNative(Native Method)
12-16 10:51:38.199: E/AndroidRuntime(767):  at java.lang.reflect.Method.invoke(Method.java:511)
12-16 10:51:38.199: E/AndroidRuntime(767):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
12-16 10:51:38.199: E/AndroidRuntime(767):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
12-16 10:51:38.199: E/AndroidRuntime(767):  at dalvik.system.NativeStart.main(Native Method)

---

我已经在 stackoverflow 中尝试了所有可能的解决方案，但都是徒劳的。请帮助我。我认为主要是 xml 到 java 显示内容存在问题。我还需要为 xml 中的每个布局输入 id 以及 java 代码如何检测要显示的布局

这里是我选择的 java 代码和 xml

    package com.example.iolcalci;

import android.app.Activity;
import android.os.Bundle;

public class Selection extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.selective);

    }

}

---

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/black"
    android:orientation="vertical" >

    <Spinner
        android:id="@+id/formulae"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="50dp"
        android:layout_marginRight="50dp"
        android:background="@color/LightSkyBlue"
        android:prompt="@string/prompt"
        android:entries="@array/formulas" />

    <TextView
        android:id="@+id/k2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignRight="@+id/k1"
        android:layout_below="@+id/k1"
        android:layout_marginTop="38dp"
        android:text="@string/K2"
        android:textColor="@color/White"
        android:textSize="25sp" />

    <TextView
        android:id="@+id/al_const"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/al"
        android:layout_below="@+id/al"
        android:layout_marginTop="44dp"
        android:text="@string/Rx"
        android:textColor="@color/White"
        android:textSize="20sp" />

    <TextView
        android:id="@+id/al"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignRight="@+id/k2"
        android:layout_below="@+id/k2"
        android:layout_marginTop="38dp"
        android:text="@string/AL"
        android:textColor="@color/White"
        android:textSize="25sp" />

    <EditText
        android:id="@+id/k2_editText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@+id/al"
        android:layout_alignRight="@+id/al_editText"
        android:layout_alignTop="@+id/k2"
        android:layout_marginLeft="120dp"
        android:background="@color/black"
        android:ems="10"
        android:inputType="numberDecimal"
        android:textColorLink="@color/white" />

    <EditText
        android:id="@+id/al_editText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignRight="@+id/formulae"
        android:layout_alignTop="@+id/al"
        android:layout_marginLeft="120dp"
        android:ems="10"
        android:inputType="numberDecimal" />

    <EditText
        android:id="@+id/al_const_editText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/al_const"
        android:layout_alignRight="@+id/al_editText"
        android:layout_marginLeft="120dp"
        android:ems="10"
        android:inputType="numberDecimal" />

    <Button
        android:id="@+id/result"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:background="@color/LightSkyBlue"
        android:text="@string/Result" />

    <EditText
        android:id="@+id/k1_editText"
        android:layout_width="wrap_content"
        android:layout_height="37dp"
        android:layout_alignLeft="@+id/k2_editText"
        android:layout_alignRight="@+id/formulae"
        android:layout_below="@+id/formulae"
        android:layout_marginTop="30dp"
        android:background="@color/black"
        android:ems="10"
        android:inputType="numberDecimal"
        android:textColorLink="@color/White" />

    <TextView
        android:id="@+id/k1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/k1_editText"
        android:layout_alignParentLeft="true"
        android:layout_marginLeft="27dp"
        android:text="@string/K1"
        android:textColor="@color/white"
        android:textSize="25sp" />

</RelativeLayout>

新的 LOGCAT

---

   12-21 10:44:50.419: W/Trace(766): Unexpected value from nativeGetEnabledTags: 0
12-21 10:44:50.573: W/Trace(766): Unexpected value from nativeGetEnabledTags: 0
12-21 10:44:50.573: W/Trace(766): Unexpected value from nativeGetEnabledTags: 0
12-21 10:44:50.923: D/AndroidRuntime(766): Shutting down VM
12-21 10:44:50.923: W/dalvikvm(766): threadid=1: thread exiting with uncaught exception (group=0x40a70930)
12-21 10:44:50.933: E/AndroidRuntime(766): FATAL EXCEPTION: main
12-21 10:44:50.933: E/AndroidRuntime(766): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.iolcalci/com.example.iolcalci.MainActivity}: java.lang.NullPointerException
12-21 10:44:50.933: E/AndroidRuntime(766):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
12-21 10:44:50.933: E/AndroidRuntime(766):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
12-21 10:44:50.933: E/AndroidRuntime(766):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
12-21 10:44:50.933: E/AndroidRuntime(766):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
12-21 10:44:50.933: E/AndroidRuntime(766):  at android.os.Handler.dispatchMessage(Handler.java:99)
12-21 10:44:50.933: E/AndroidRuntime(766):  at android.os.Looper.loop(Looper.java:137)
12-21 10:44:50.933: E/AndroidRuntime(766):  at android.app.ActivityThread.main(ActivityThread.java:5039)
12-21 10:44:50.933: E/AndroidRuntime(766):  at java.lang.reflect.Method.invokeNative(Native Method)
12-21 10:44:50.933: E/AndroidRuntime(766):  at java.lang.reflect.Method.invoke(Method.java:511)
12-21 10:44:50.933: E/AndroidRuntime(766):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
12-21 10:44:50.933: E/AndroidRuntime(766):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
12-21 10:44:50.933: E/AndroidRuntime(766):  at dalvik.system.NativeStart.main(Native Method)
12-21 10:44:50.933: E/AndroidRuntime(766): Caused by: java.lang.NullPointerException
12-21 10:44:50.933: E/AndroidRuntime(766):  at com.example.iolcalci.MainActivity.onCreate(MainActivity.java:23)
12-21 10:44:50.933: E/AndroidRuntime(766):  at android.app.Activity.performCreate(Activity.java:5104)
12-21 10:44:50.933: E/AndroidRuntime(766):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
12-21 10:44:50.933: E/AndroidRuntime(766):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
12-21 10:44:50.933: E/AndroidRuntime(766):  ... 11 more

---

list 文件

    <?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.iolcalci"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="17" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.iolcalci.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name="Selection"
            android:exported="false"
            android:configChanges="orientation|keyboardHidden|screenSize"
            android:label="@string/app_name">
                <intent-filter>
                <action android:name="com.example.iolcalci.MAIN" />
                <category android:name="android.intent.category.DEFAULT" />
          </intent-filter>
        </activity>
    </application>

</manifest>

Answer 1

从您的代码来看，我将推测这一行导致了错误:

setContentView(R.id.selection);

无需更改您从中调用“选择” Activity 的 Activity 的 contentView。你应该仔细阅读 Intent 。我假设单击按钮时，您希望弹出新 Activity 及其内容。为此，请执行以下操作:

try{
                iol.setOnClickListener(new View.OnClickListener() {


                        @Override
                        public void onClick(View v) {
                            // TODO Auto-generated method stub
                           Intent iolIntent=new Intent(FullscreenActivity.this,Selection.class);
                startActivity(iolIntent);
                        }
                });
            }

同时将按钮的布局宽度和布局高度设置为“wrap_content”。明确的测量不会很好地工作，因为有许多可能的分辨率。

android:layout_height="wrap_content"
android:layout_width="wrap_content"

如果有更多错误，请发布新的 logcat。

我在你的 selection.java 中找到了这个:

setContentView(R.layout.selective);

这意味着您的 res/layout/文件夹中应该有一个 selective.xml 文件。

这个 selective.xml 文件应该包含 EditText 的定义。例如，

<EditText
    android:id="@+id/k1_editText"
    android:layout_width="wrap_content"
    android:layout_height="37dp"
    android:layout_alignLeft="@+id/k2_editText"
    android:layout_alignRight="@+id/formulae"
    android:layout_below="@+id/formulae"
    android:layout_marginTop="30dp"
    android:background="@color/black"
    android:ems="10"
    android:inputType="numberDecimal"
    android:textColorLink="@color/White" />

您需要使用这段代码在 Activity 文件中引用它:

EditText ed=new EditText findViewById(R.id.k2_editText);

现在将显示 EditText 字段。

如果你想让你的 EditText 对象成为全局对象，在类中声明它，然后在设置内容 View 后初始化它。像这样，

public class Selection extends Activity {
EditText ed;
@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.selective);
    EditText ed=new EditText findViewById(R.id.k2_editText);
}

确保您始终在创建 Activity 和设置内容 View 之后初始化小部件对象，否则编译器将不得不初始化尚未引用的内容。只有在设置内容 View 后才会引用布局文件。只有在设置布局文件后，您才能将对象初始化为布局文件中存在的任何内容。

如果您喜欢这个答案，请投上一票。