Question

我知道这个错误在论坛上出现了数百万次，但请帮助我找到我错过的内容。我正在尝试使用简单的面向标签的应用程序，我没有太多（除了错误）

1）我的主要活动是基于我找到的tablayout教程

public class MainTabPanel extends TabActivity {

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.mainlayout);
        Resources res = getResources();
        TabHost tabHost = getTabHost();
        TabHost.TabSpec spec;
        Intent intent;
        intent = new Intent().setClass(this, MyBookActivity.class);
        spec = tabHost.newTabSpec("main")
                .setIndicator("Main", res.getDrawable(R.drawable.ic_mybook))
                .setContent(intent);
        tabHost.addTab(spec);
        tabHost.setCurrentTab(0);
    }

}

2）mainlayout.xml

<?xml version="1.0" encoding="utf-8"?>
<TabHost xmlns:android="http://schemas.android.com/apk/res/android"
 android:id="@android:id/tabhost"
 android:layout_width="fill_parent"
 android:layout_height="fill_parent">
 <LinearLayout  
   android:orientation="vertical"  
   android:layout_width="fill_parent"     
   android:layout_height="fill_parent"        
   android:padding="5dp">
 <TabWidget 
  android:id="@android:id/tabs" 
  android:layout_width="fill_parent"
  android:layout_height="wrap_content" />        

  <FrameLayout      
  android:id="@android:id/tabcontent" 
  android:layout_width="fill_parent"   
  android:layout_height="fill_parent"
  android:padding="5dp" />   
 </LinearLayout></TabHost>

3）我的第二个活动基本上是空的，它只是显示当前的日期和时间，在我尝试添加标签面板之前工作

4）我的清单文件

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="org.th.mybook"
    android:versionCode="1"
    android:versionName="1.0" >
    <uses-sdk android:minSdkVersion="8" />
    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:name=".MainTabPanel"
            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="MyBookActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.ALTERNATIVE" />
            </intent-filter>
        </activity>
    </application>
</manifest>

5 log cat错误

02-10 21:04:45.203: E/AndroidRuntime(1107): FATAL EXCEPTION: main
02-10 21:04:45.203: E/AndroidRuntime(1107): java.lang.RuntimeException: Unable to start activity ComponentInfo{org.th.mybook/org.th.mybook.MainTabPanel}: java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{org.th.mybook/org.th.mybook.MyBookActivity}: java.lang.NullPointerException
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.app.ActivityThread.access$2300(ActivityThread.java:125)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.os.Handler.dispatchMessage(Handler.java:99)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.os.Looper.loop(Looper.java:123)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.app.ActivityThread.main(ActivityThread.java:4627)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at java.lang.reflect.Method.invokeNative(Native Method)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at java.lang.reflect.Method.invoke(Method.java:521)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at dalvik.system.NativeStart.main(Native Method)
02-10 21:04:45.203: E/AndroidRuntime(1107): Caused by: java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{org.th.mybook/org.th.mybook.MyBookActivity}: java.lang.NullPointerException
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.app.ActivityThread.startActivityNow(ActivityThread.java:2503)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:127)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:339)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:651)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.widget.TabHost.setCurrentTab(TabHost.java:323)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.widget.TabHost.addTab(TabHost.java:213)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at org.th.mybook.MainTabPanel.onCreate(MainTabPanel.java:30)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
02-10 21:04:45.203: E/AndroidRuntime(1107):     ... 11 more
02-10 21:04:45.203: E/AndroidRuntime(1107): Caused by: java.lang.NullPointerException
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:100)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at org.th.mybook.MyBookActivity.<init>(MyBookActivity.java:16)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at java.lang.Class.newInstanceImpl(Native Method)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at java.lang.Class.newInstance(Class.java:1429)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
02-10 21:04:45.203: E/AndroidRuntime(1107):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2577)
02-10 21:04:45.203: E/AndroidRuntime(1107):     ... 20 more

请帮助我，并告诉我我错过了什么，我将这段代码与我的旧代码进行比较，我找不到任何东西问候

6）我的书活动

public class MyBookActivity extends Activity {
    java.text.DateFormat dateFormat = android.text.format.DateFormat.getDateFormat(getApplicationContext()); 

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        DigitalClock clock = (DigitalClock) findViewById(R.id.digitalClock1);
        final TextView date = (TextView) findViewById(R.id.textView1);
        date.setText(dateFormat.format(new Date()));
        TextWatcher watcher = new TextWatcher() {

            @Override
            public void afterTextChanged(Editable s) {
            }

            @Override
            public void beforeTextChanged(CharSequence s, int start, int count,
                    int after) {
            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before,
                    int count) {

                if (s.toString().startsWith("00:00:00")
                        || s.toString().startsWith("12:00:00")) {
                    date.setText(dateFormat.format(new Date()));
                }
            }
        };
        clock.addTextChangedListener(watcher);

    }
}

7）main.xml布局 - ＆gt;我的书活动

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:gravity="right"
    android:orientation="horizontal" >


    <LinearLayout
        android:id="@+id/DatePanel1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" >


        <TextView
            android:id="@+id/textView1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginRight="@dimen/space"
            android:layout_weight="1"
            android:text="TextView" />

        <DigitalClock
            android:id="@+id/digitalClock1"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="DigitalClock" />
    </LinearLayout>

</LinearLayout>

Answer 1

    <activity
        android:name="MyBookActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.ALTERNATIVE" />
        </intent-filter>
    </activity>

MyBookActivity之前的点在哪里？

Answer 2

这是我自己的愚蠢：

java.text.DateFormat dateFormat = android.text.format.DateFormat.getDateFormat(getApplicationContext());

将这个放在onCreate()方法中解决了我的问题。

Answer 3

您的Manifest必须更改此活动名称必须指定为".YourActivityname"

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

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

<application
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name" >
    <activity
        android:name=".MainTabPanel"
        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=".MyBookActivity"  >            
    </activity>
</application>

Answer 4

我有同样的问题，我清理并重建了项目，但它确实有效。

Answer 5

亲爱的你在你的Manifest中使用了两个Intent启动器。仅将一个活动作为启动器：您的清单活动是：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="org.th.mybook"
    android:versionCode="1"
    android:versionName="1.0" >
    <uses-sdk android:minSdkVersion="8" />
    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:name=".MainTabPanel"
            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="MyBookActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.ALTERNATIVE" />
            </intent-filter>
        </activity>
    </application>
</manifest>

现在编写代码（我已经制作了你的＆＃39; MyActivityBook＆＃39;你的默认活动启动器。将它复制并粘贴到你的清单上。

<?xml version="1.0" encoding="utf-8"?>
    <manifest xmlns:android="http://schemas.android.com/apk/res/android"
        package="org.th.mybook"
        android:versionCode="1"
        android:versionName="1.0" >
        <uses-sdk android:minSdkVersion="8" />
        <application
            android:icon="@drawable/ic_launcher"
            android:label="@string/app_name" >
            <activity
                android:name=".MainTabPanel"
                android:label="@string/app_name" >

            </activity>
            <activity
                android:name="MyBookActivity"
                android:label="@string/app_name" >
                <intent-filter>
                    <action android:name="android.intent.action.MAIN" />
                    <category android:name="android.intent.category.LAUNCHER" />
                </intent-filter>
            </activity>
        </application>
    </manifest>

，如果您复制粘贴旧代码，则可能会出现第二个错误，请更新 com.example.packagename.FILE_NAME

希望这会奏效！

Answer 6

我的问题看起来很相似，几个小时后我发现我的项目并没有全部转换成androidx，所以我改变了：

<android.support.constraint.ConstraintLayout

进入

<androidx.constraintlayout.widget.ConstraintLayout

然后 androidStudio 仍然抱怨，但问题解决者可以将约束布局添加到您的库左右。

现在又开始了！有趣的是，在过去的 8 年中，许多类似的问题出现在不同的解决方案中。

java.lang.RuntimeException：无法启动活动ComponentInfo

6 个答案: