1.限制edittext的可输入内容

app/src/main/res/layout/activity_login.xml

                     android:textColor="@color/black"
                     android:textColorHint="#FFB8C2D9"
                     android:textSize="21sp"
+                    android:maxLength="20"
                     app:layout_constraintLeft_toLeftOf="parent"
                     app:layout_constraintRight_toRightOf="parent"
                     app:layout_constraintTop_toTopOf="parent" />
                     android:textColor="@color/black"
                     android:textColorHint="#FFB8C2D9"
                     android:textSize="21sp"
+                    android:maxLength="20"
                     app:layout_constraintLeft_toLeftOf="parent"
                     app:layout_constraintRight_toRightOf="parent"
                     app:layout_constraintTop_toTopOf="parent" />
                 android:paddingLeft="28dp"
                 android:paddingRight="28dp"
                 android:singleLine="true"
+                android:maxLength="20"
                 android:textColor="@color/codetipscolor"
                 android:textColorHint="@color/codehintcolor"
                 android:textSize="16sp" />

app/src/main/res/layout/activity_main.xml

                 android:layout_width="100dp"
                 android:layout_height="100dp"
                 android:text="管理页面"
-                android:visibility="gone" />
+                android:visibility="visible" />
 
 
             <LinearLayout

app/src/main/res/layout/layout_changecode_dialog.xml

                     android:gravity="center_vertical"
                     android:hint="@string/oldcodetips"
                     android:singleLine="true"
+                    android:maxLength="16"
                     android:textColor="@color/black"
                     android:textColorHint="#FFB8C2D9"
                     android:textSize="16sp" />
                     android:gravity="center_vertical"
                     android:hint="@string/newcodetips"
                     android:singleLine="true"
+                    android:maxLength="16"
                     android:textColor="@color/black"
                     android:textColorHint="#FFB8C2D9"
                     android:textSize="16sp" />
                     android:gravity="center_vertical"
                     android:hint="@string/enternewcodetips"
                     android:singleLine="true"
+                    android:maxLength="16"
                     android:textColor="@color/black"
                     android:textColorHint="#FFB8C2D9"
                     android:textSize="16sp" />