java Android应用程序无法启动活动

Question

我想知道为什么它不能打开新的java类。 当我尝试开始新的活动时，它将崩溃

public class MainActivity extends ActionBarActivity {
    EditText emailEt;
    TextView registerET;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        emailEt = (EditText) findViewById(R.id.email);
        registerET = (TextView) findViewById(R.id.register);
        registerET.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                Log.i("clicks","You Clicked register page");
                Intent myIntent = new Intent(MainActivity.this, RegisterActivity.class);
                startActivity(myIntent);
                MainActivity.this.finish();
            }
        });
    }
    public void OnLogin(View view) {
        String username = emailEt.getText().toString();
        String type = "login";
        BackgroundWorker backgroundWorker = new BackgroundWorker(this);
        backgroundWorker.execute(type, username);
    }

}

可能有问题吗？我把它放错活动的位置了吗

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:安卓="http://schemas.安卓.com/apk/res/安卓"
package="com.example.a20_1discussboard">
<uses-permission 安卓:name="安卓.permission.INTERNET"></uses-permission>"
<application
    安卓:allowBackup="true"
    安卓:label="@string/app_name"
    安卓:theme="@style/AppTheme" >
    <activity
        安卓:name=".MainActivity"
        安卓:label="@string/app_name" >
        <intent-filter>
            <action 安卓:name="安卓.intent.action.MAIN" />
            <category 安卓:name="安卓.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>
    <activity 安卓:label="@string/app_name" 安卓:name=".RegisterActivity"/>
</manifest>

看起来可以打开新的java类，但它仍然显示MainActivity。 错误日志：

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.a20_1discussboard, PID: 2194
                  java.lang.IllegalStateException: Could not find method onClick(View) in a parent or ancestor Context for 安卓:onClick attribute defined on view class 安卓.support.v7.widget.AppCompatTextView with id 'register'
                      at 安卓.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.resolveMethod(AppCompatViewInflater.java:327)
                      at 安卓.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:284)
                      at 安卓.view.View.performClick(View.java:4780)
                      at 安卓.view.View$PerformClick.run(View.java:19866)
                      at 安卓.os.Handler.handleCallback(Handler.java:739)
                      at 安卓.os.Handler.dispatchMessage(Handler.java:95)
                      at 安卓.os.Looper.loop(Looper.java:135)
                      at 安卓.app.ActivityThread.main(ActivityThread.java:5254)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at java.lang.reflect.Method.invoke(Method.java:372)
                      at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
                      at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:698)

Answer 1

在AndroidManifest中的应用程序中尝试声明的活动。像这样的xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.a20_1discussboard">
<uses-permission android:name="android.permission.INTERNET"></uses-permission>"
<application
    android:allowBackup="true"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name=".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:label="@string/app_name"
              android:name=".RegisterActivity"/>
</application>
</manifest>

Answer 2

确保将RegisterActivity添加到AndroidManifest.xml内<application>标记中：

<application ...>

    ...

    <activity
       android:label="@string/app_name"   
       android:name=".RegisterActivity"/>

</application>

Answer 3

从onCreate方法中删除此行：MainActivity.this.finish();

如果要停止或暂停MainActivity，请使用：

@Override
public void onPause() { } 

或

@Override
public void onStop() { }

在活动课上

Answer 4

谢谢大家
将RegisterActivity添加到AndroidManifest.xml内的<application>标记并删除MainActivity.this.finish()

它现在正在工作

Answer 5

放置正确的Menifest格式：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.a20_1discussboard">
<uses-permission android:name="android.permission.INTERNET"></uses-permission>"
<application
android:allowBackup="true"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
    android:name=".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:label="@string/app_name"     
          android:name=".RegisterActivity"/>   //<---here
</application>
</manifest>

不要调用finish()，这会导致崩溃：

    registerET.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            Log.i("clicks","You Clicked register page");
            Intent myIntent = new Intent(MainActivity.this, RegisterActivity.class);
            startActivity(myIntent);
            //remove finish();
        }
    });