Question

我正在创建一个简单的应用程序，我试图显示标签，但它拒绝显示。这是android清单：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="r.gabriel.ecuacionesdesegundogrado" >
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:theme="@style/AppTheme"
        android:label="Ecuación de Segundo Grado">
        <activity
            android:name=".MainActivity"
            android:label="Ecuación de Segundo Grado">
            <intent-filter android:label="Ecuación de Segundo Grado">
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

ActivityMain：

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    } 
}

activity_main.xml代码：

<LinearLayout 
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MainActivity"
    android:background="@color/custom_grey" >
        <TableLayout android:layout_width="fill_parent"
            android:layout_height="fill_parent">
            <TableRow>
                <TextView android:text="@string/custom_instructions"
                    android:layout_weight="1"
                    android:ellipsize="none"
                    android:maxLines="100"
                    android:scrollHorizontally="false"/>
            </TableRow>

            <!-- input a -->
            <TableRow 
                android:weightSum="100">
                <TextView
                    android:text="@string/custom_a"
                    android:layout_width="0dp"
                    android:layout_weight="40"/>
                <EditText
                    android:id="@+id/inputA"
                    android:hint="@string/custom_dummyText"
                    android:layout_width="0dp"
                    android:layout_weight="60"/>
            </TableRow>

            <!-- input b -->
            <TableRow 
                android:weightSum="100">
                <TextView
                    android:text="@string/custom_b"
                    android:layout_width="0dp"
                    android:layout_weight="40"/>
                <EditText
                    android:id="@+id/inputB"
                    android:hint="@string/custom_dummyText"
                    android:layout_width="0dp"
                    android:layout_weight="60"/>
            </TableRow>

            <!-- input c -->
            <TableRow 
                 android:weightSum="100">
                 <TextView
                     android:text="@string/custom_c"
                     android:layout_width="0dp"
                     android:layout_weight="40"/>
                 <EditText
                     android:id="@+id/inputC"
                     android:hint="@string/custom_dummyText"
                     android:layout_width="0dp"
                     android:layout_weight="60"/>
            </TableRow>

            <!-- answer -->
            <TableRow 
                android:layout_weight="1" 
                android:weightSum="100" 
                android:layout_height="wrap_content">
                <TextView
                    android:text="@string/custom_solution"
                    android:layout_width="0dp"
                    android:layout_height="fill_parent"
                    android:layout_weight="100"
                    android:gravity="center"
                    android:textSize="25sp"
                    android:ellipsize="none"
                    android:maxLines="100"
                    android:scrollHorizontally="false"/>
            </TableRow>
    </TableLayout>
</LinearLayout>

在android studio预览版中，不会显示android：标签，就像在物理设备和模拟器上运行一样。

Answer 1

以下是在应用启动时只显示字符串的代码。试试这个。如果可行，请尝试在XML布局文件中添加TableLayout。

<强> ActivityMain.java

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        TextView textView = (TextView) findViewById(R.id.textView1);
        textView.setText("Ecuación de Segundo Grado");
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    } 
}

这是布局文件 activity_main.xml

<LinearLayout 
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MainActivity"
    android:background="@color/custom_grey" >
        <TextView
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:id="@+id/textView1"
                android:gravity="center_horizontal"
                android:textSize="22sp"/>
</LinearLayout>

<强> menu_main.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      xmlns:tools="http://schemas.android.com/tools">
    <item android:id="@+id/main_menu"
          android:title="Ecuación de Segundo Grado"
          app:showAsAction="ifRoom"/>
</menu>

为什么android：标签不存在？

1 个答案: