Question

我正在练习构建按钮（所有测试都很好），所以我要继续使用小部件。现在，当我在Android Studio中运行时，它显示我的构建成功，按钮显示在我的预览屏幕上，但我手机上的应用程序完全空白。

这是我的.java

package com.android.woo.datetimepickerdialog;

import android.app.DatePickerDialog;
import android.app.TimePickerDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.DatePicker;
import android.widget.EditText;
import android.widget.TimePicker;

import com.example.android.woo.R;

import java.util.Calendar;

public class MainActivity extends AppCompatActivity implements
        View.OnClickListener {

    Button btnDatePicker, btnTimePicker;
    EditText txtDate, txtTime;
    private int mYear, mMonth, mDay, mHour, mMinute;

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

        btnDatePicker=(Button)findViewById(R.id.btn_date);
        btnTimePicker=(Button)findViewById(R.id.btn_time);
        txtDate=(EditText)findViewById(R.id.in_date);
        txtTime=(EditText)findViewById(R.id.in_time);

        btnDatePicker.setOnClickListener(this);
        btnTimePicker.setOnClickListener(this);

    }
    @Override
    public void onClick(View v) {

        if (v == btnDatePicker) {

            // Get Current Date
            final Calendar c = Calendar.getInstance();
            mYear = c.get(Calendar.YEAR);
            mMonth = c.get(Calendar.MONTH);
            mDay = c.get(Calendar.DAY_OF_MONTH);
            DatePickerDialog datePickerDialog = new DatePickerDialog(this,
                    new DatePickerDialog.OnDateSetListener() {

                        @Override
                        public void onDateSet(DatePicker view, int year,
                                              int monthOfYear, int dayOfMonth) {

                            txtDate.setText(dayOfMonth + "-" + (monthOfYear + 1) + "-" + year);

                        }
                    }, mYear, mMonth, mDay);
            datePickerDialog.show();
        }
        if (v == btnTimePicker) {

            // Get Current Time
            final Calendar c = Calendar.getInstance();
            mHour = c.get(Calendar.HOUR_OF_DAY);
            mMinute = c.get(Calendar.MINUTE);

            // Launch Time Picker Dialog
            TimePickerDialog timePickerDialog = new TimePickerDialog(this,
                    new TimePickerDialog.OnTimeSetListener() {

                        @Override
                        public void onTimeSet(TimePicker view, int hourOfDay,
                                              int minute) {

                            txtTime.setText(hourOfDay + ":" + minute);
                        }
                    }, mHour, mMinute, false);
            timePickerDialog.show();
        }
    }
}

这是我的activity_main.xml

<RelativeLayout 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">

    <EditText
        android:layout_width="200dp"
        android:layout_height="wrap_content"
        android:id="@+id/in_date"
        android:layout_marginTop="82dp"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="SELECT DATE"
        android:id="@+id/btn_date"
        android:layout_alignBottom="@+id/in_date"
        android:layout_toRightOf="@+id/in_date"
        android:layout_toEndOf="@+id/in_date" />
    <EditText
        android:layout_width="200dp"
        android:layout_height="wrap_content"
        android:id="@+id/in_time"
        android:layout_below="@+id/in_date"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="SELECT TIME"
        android:id="@+id/btn_time"
        android:layout_below="@+id/btn_date"
        android:layout_alignLeft="@+id/btn_date"
        android:layout_alignStart="@+id/btn_date" />

    </RelativeLayout>

添加我的清单以供审核：

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

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="Woo"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

Answer 1

查看manifest.xml以确保您的MainActivity是启动器活动：

<activity android:name=".MainActivity">
    <intent-filter>
        <action android:name="android.intent.action.MAIN"/>

        <category android:name="android.intent.category.LAUNCHER"/>
    </intent-filter>
</activity>

如果这样做，请检查您的activity_main.xml是否还有其他变体：

例如，如果您的测试设备是平板电脑而且您的xlarge布局为空，则您将看不到任何内容。

Answer 2

尝试

import com.example.android.woo.datetimepickerdialog.R;

按钮显示在预览中但不在手机上显示

2 个答案: