所遇到的问题

1、ImageView控件与EditView控件无法放置在同一行-----放置在水平线性布局里

2、Button按钮的背景色调整

android:background="@android:color/transparent" 背景色设置为透明

解决办法

找到项目中的这两个xml文件，将 parent="Theme.MaterialComponents.DayNight.DarkActionBar" 修改为 parent="Theme.MaterialComponents.DayNight.DarkActionBar.Bridge" 即可解决，注意两个文件都要修改。若修改后没反应,可尝试关闭Android Studio并重新启动

3、界面之间的跳转Intent intent = new Intent(MainActivity.this,MainActivity2.class);//"MainActivity2.class"是所要跳转到的界面位置

startActivity(intent);

4、TextView字体的自定义

(1)下载所想要的字体文件（.TTF）

(2)Project--app--src--mian--右键Directory,命名为assets--再次新建文件夹fonts,然后将下载的字体文件放到fonts文件夹中

?(3)在对应的.java文件中进行字体代码修改

//获取控件

TextView wen = findViewById(R.id.wen);

//设置字体

Typeface typeface = Typeface.createFromAsset(getAssets(),"fonts/KaiTi.TTF");

//"fonts/KaiTi.TTF"是字体文件

wen.setTypeface(typeface);

5、界面之间的数据传递

（1）在所要传出数据的界面

//实例化窗口，并指定数据从哪个窗口传到哪个窗口
Intent intent = new Intent(MainActivity3.this, MainActivity.class);
//"MainActivity3.this"是当前窗口，"MainActivity.class"是获取数据的窗口
//将数据传到intent中
intent.putExtra("f_p", fix_pwd.getText().toString());
//开始跳转界面
startActivity(intent);

（2）接收数据界面

//获取intent对象
Intent intent = getIntent();
//将获取的数据赋给password
String password = intent.getStringExtra("f_p");

(6、做AS调取相机拍照加保存图像时，下面这行代码出现问题

path=cursor.getString(cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA));

报错是：Value must be ≥ 0

解决方法：把getColumnIndex换为getColumnIndexOrThrow可以运行

7、遇到“Cannot resolve?symbol”

解决方法：在AS中点击“File” -> “Invalidate Caches / Restart”，对话框选择?“Invalidate and Restart”，清空 cache 并且重启。)

项目展示

登陆界面源码

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.text.method.HideReturnsTransformationMethod;
import android.text.method.PasswordTransformationMethod;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    //定义控件
    private EditText name;
    private EditText pwd;
    private CheckBox show_pwd;
    private Button forget_pwd;
    private Button sign;

    //定义用户名和密码
    String user = "admin";
    String password = "123456";

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

    //控件实例化
    public void view(){
        name = findViewById(R.id.name);
        pwd = findViewById(R.id.pwd);
        show_pwd = findViewById(R.id.show_pwd);
        forget_pwd = findViewById(R.id.forget_pwd);
        sign = findViewById(R.id.sign);
    }

    //功能实现
    public void even(){
        //复选框的点击事件
        //给CheckBox设置事件监听
        show_pwd.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton compoundButton, boolean isChecked) {
                if(isChecked){
                    pwd.setTransformationMethod(HideReturnsTransformationMethod.getInstance());
                }else {
                    pwd.setTransformationMethod(PasswordTransformationMethod.getInstance());
                }
            }
        });

        //按钮点击事件
        //按钮1:忘记密码
        forget_pwd.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Toast.makeText(MainActivity.this, "点击重新设置密码", Toast.LENGTH_SHORT).show();
                Intent intent = new Intent(MainActivity.this,FixActivity.class);
                startActivity(intent);

            }
        });
        //按钮2:登录
        sign.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String n = name.getText().toString();
                String p = pwd.getText().toString();
                boolean isFix = getIntent().getBooleanExtra("revise",false);

                if (!isFix){
                    //判断用户名和密码
                    if (n.equals(user)&&p.equals(password)){
                        Toast.makeText(MainActivity.this, "登录成功!", Toast.LENGTH_SHORT).show();
                        Intent intent = new Intent(MainActivity.this,TextActivity.class);
                        startActivity(intent);
                    }else if (n.equals("")||p.equals("")){
                        Toast.makeText(MainActivity.this, "用户名或密码不能为空!!!", Toast.LENGTH_SHORT).show();
                    }else {
                        Toast.makeText(MainActivity.this, "用户名或密码错误!!!", Toast.LENGTH_SHORT).show();
                    }
                }else {
                    String password2 = getIntent().getStringExtra("f_p");
                    //判断用户名和密码
                    if (n.equals(user)&&p.equals(password2)){
                        Toast.makeText(MainActivity.this, "登录成功!", Toast.LENGTH_SHORT).show();
                        Intent intent = new Intent(MainActivity.this,TextActivity.class);
                        startActivity(intent);
                    }else if (n.equals("")||p.equals("")){
                        Toast.makeText(MainActivity.this, "用户名或密码不能为空!!!", Toast.LENGTH_SHORT).show();
                    }else {
                        Toast.makeText(MainActivity.this, "用户名或密码错误!!!", Toast.LENGTH_SHORT).show();
                    }
                }
            }
        });
    }

}

TextView控件字体修改

package com.example.mytest2;

import androidx.appcompat.app.AppCompatActivity;

import android.graphics.Typeface;
import android.os.Bundle;
import android.widget.TextView;

public class MainActivity2 extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        //获取控件
        TextView wen = findViewById(R.id.wen);
        //设置字体
        Typeface typeface = Typeface.createFromAsset(getAssets(),"fonts/KaiTi.TTF");
        wen.setTypeface(typeface);
    }
}

忘记密码部分代码

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class FixActivity extends AppCompatActivity {

    //定义控件
    private EditText new_pwd;
    private EditText fix_pwd;
    private Button but_fix;

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

    //控件实例化
    public void view(){
        new_pwd = findViewById(R.id.new_pwd);
        fix_pwd = findViewById(R.id.fix_pwd);
        but_fix = findViewById(R.id.but_fix);
    }

    //功能实现
    public void even(){
        but_fix.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String n_p = new_pwd.getText().toString();
                String f_p = fix_pwd.getText().toString();
                boolean isFix = true;

//                if (n_p.equals(f_p)){
//                    Toast.makeText(MainActivity3.this, "密码修改成功!", Toast.LENGTH_SHORT).show();
//                    Intent intent = new Intent(MainActivity3.this,MainActivity.class);
//                    intent.putExtra("f_p",f_p);
//                    startActivity(intent);
//                }else if (n_p.equals("")||f_p.equals("")){
//                    Toast.makeText(MainActivity3.this, "新密码不能为空!!!", Toast.LENGTH_SHORT).show();
//                }else {
//                    Toast.makeText(MainActivity3.this, "两次密码不一致  !!!", Toast.LENGTH_SHORT).show();
//                }
                if (!n_p.equals("")&&!f_p.equals("")){
                    if (n_p.equals(f_p)) {
                        Toast.makeText(FixActivity.this, "密码修改成功!", Toast.LENGTH_SHORT).show();
                        Intent intent = new Intent(FixActivity.this, MainActivity.class);
                        intent.putExtra("f_p", f_p);
                        intent.putExtra("revise",isFix);
                        startActivity(intent);
                    }else{
                        Toast.makeText(FixActivity.this, "两次密码不一致  !!!", Toast.LENGTH_SHORT).show();
                    }
                }else{
                    Toast.makeText(FixActivity.this, "新密码不能为空!!!", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
}