fix(dialog): improved handling of scrollable content

* Improves the handling of scrollable content inside the `mat-dialog-content` by using flexbox, rather than a hardcoded `max-height`, to define the content height. This resolves various issues where the dialog would go out of the screen at certain screen sizes or have multiple scrollbars.
* Uses flexbox to ensure that the dialog content elements are always at the appropriate size.

Fixes angular#2481.
Fixes angular#3239.
Fixes angular#6584.
Fixes angular#8493.

src/demo-app/dialog/dialog-demo.html

@@ -6,9 +6,13 @@ <h1>Dialog demo</h1>
 <button mat-raised-button color="accent" (click)="openContentElement()">
   Open dialog with content elements
 </button>
-<button mat-raised-button color="accent" (click)="openTemplate()">
+<button mat-raised-button color="accent" (click)="openTemplate(templateDialog)">
   Open dialog with template content
 </button>
+<button mat-raised-button color="accent" (click)="openTemplate(templateDialogWithContent)">
+  Open template dialog with content elements
+</button>
+
 
 <mat-card class="demo-dialog-card">
   <mat-card-content>
@@ -111,7 +115,7 @@ <h2>Other options</h2>
 <p>Last afterClosed result: {{lastAfterClosedResult}}</p>
 <p>Last beforeClose result: {{lastBeforeCloseResult}}</p>
 
-<ng-template let-data let-dialogRef="dialogRef">
+<ng-template #templateDialog let-data let-dialogRef="dialogRef">
   I'm a template dialog. I've been opened {{numTemplateOpens}} times!
 
   <p>It's Jazz!</p>
@@ -122,6 +126,34 @@ <h2>Other options</h2>
   </mat-form-field>
 
   <p> {{ data.message }} </p>
-  <button type="button" (click)="dialogRef.close(howMuch.value)">Close dialog</button>
-  <button (click)="dialogRef.updateSize('500px', '500px').updatePosition({ top: '25px', left: '25px' });">Change dimensions</button>`
+  <button type="button" (click)="dialogRef.close(lastCloseResult = howMuch.value)">Close dialog</button>
+  <button (click)="dialogRef.updateSize('500px', '500px').updatePosition({ top: '25px', left: '25px' });">Change dimensions</button>
+</ng-template>
+
+<ng-template #templateDialogWithContent let-data let-dialogRef="dialogRef">
+  <h2 mat-dialog-title>Saturn</h2>
+
+  <mat-dialog-content>
+    <img style="max-width: 100%;" src="https://upload.wikimedia.org/wikipedia/commons/thumb/c/c7/Saturn_during_Equinox.jpg/1920px-Saturn_during_Equinox.jpg" alt="Saturn">
+    Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after
+    Jupiter. It is a gas giant with an average radius about nine times that of Earth. It has
+    only one-eighth the average density of Earth, but with its larger volume Saturn is over
+    95 times more massive. Saturn is named after the Roman god of agriculture; its astronomical
+    symbol (♄) represents the god's sickle.
+
+    Saturn's interior is probably composed of a core of iron–nickel and rock
+    (silicon and oxygen compounds). This core is surrounded by a deep layer of metallic hydrogen,
+    an intermediate layer of liquid hydrogen and liquid helium, and finally a gaseous outer layer.
+    Saturn has a pale yellow hue due to ammonia crystals in its upper atmosphere. Electrical
+    current within the metallic hydrogen layer is thought to give rise to Saturn's planetary
+    magnetic field, which is weaker than Earth's, but has a magnetic moment 580 times that of
+    Earth due to Saturn's larger size. Saturn's magnetic field strength is around one-twentieth
+    of Jupiter's. The outer atmosphere is generally bland and lacking in contrast, although
+    long-lived features can appear. Wind speeds on Saturn can reach 1,800 km/h (1,100 mph),
+    higher than on Jupiter, but not as high as those on Neptune.
+  </mat-dialog-content>
+
+  <mat-dialog-actions>
+    <button mat-raised-button color="primary" (click)="dialogRef.close()">Close dialog</button>
+  </mat-dialog-actions>
 </ng-template>

src/demo-app/dialog/dialog-demo.ts

@@ -29,12 +29,12 @@ export class DialogDemo {
     panelClass: 'custom-overlay-pane-class',
     hasBackdrop: true,
     backdropClass: '',
-    width: '',
-    height: '',
-    minWidth: '',
-    minHeight: '',
+    width: defaultDialogConfig.width,
+    height: defaultDialogConfig.height,
+    minWidth: defaultDialogConfig.minWidth,
+    minHeight: defaultDialogConfig.minHeight,
     maxWidth: defaultDialogConfig.maxWidth,
-    maxHeight: '',
+    maxHeight: defaultDialogConfig.maxHeight,
     position: {
       top: '',
       bottom: '',
@@ -47,8 +47,6 @@ export class DialogDemo {
   };
   numTemplateOpens = 0;
 
-  @ViewChild(TemplateRef) template: TemplateRef<any>;
-
   constructor(public dialog: MatDialog, @Inject(DOCUMENT) doc: any) {
     // Possible useful example for the open and closeAll events.
     // Adding a class to the body if a dialog opens and
@@ -80,9 +78,9 @@ export class DialogDemo {
     dialogRef.componentInstance.actionsAlignment = this.actionsAlignment;
   }
 
-  openTemplate() {
+  openTemplate(template: TemplateRef<any>) {
     this.numTemplateOpens++;
-    this.dialog.open(this.template, this.config);
+    this.dialog.open(template, this.config);
   }
 }
 

src/lib/dialog/dialog-config.ts

@@ -75,7 +75,7 @@ export class MatDialogConfig<D = any> {
   maxWidth?: number | string = '80vw';
 
   /** Max-height of the dialog. If a number is provided, pixel units are assumed. */
-  maxHeight?: number | string;
+  maxHeight?: number | string = '80vh';
 
   /** Position overrides. */
   position?: DialogPosition;

src/lib/dialog/dialog-container.html

@@ -1 +1,3 @@
-<ng-template cdkPortalOutlet></ng-template>
+<div class="mat-dialog-component-host">
+  <ng-template cdkPortalOutlet></ng-template>
+</div>

src/lib/dialog/dialog-container.ts

@@ -113,7 +113,15 @@ export class MatDialogContainer extends BasePortalOutlet {
     }
 
     this._savePreviouslyFocusedElement();
-    return this._portalOutlet.attachComponentPortal(portal);
+
+    const componentRef = this._portalOutlet.attachComponentPortal(portal);
+
+    // We need to add an extra class to the root of the instantiated component, which
+    // allows us to propagate some width/height overrides down from the overlay pane.
+    componentRef.location.nativeElement.classList.add('mat-dialog-component-host');
+    this._toggleScrollableContentClass();
+
+    return componentRef;
   }
 
   /**
@@ -126,7 +134,9 @@ export class MatDialogContainer extends BasePortalOutlet {
     }
 
     this._savePreviouslyFocusedElement();
-    return this._portalOutlet.attachTemplatePortal(portal);
+    const viewRef = this._portalOutlet.attachTemplatePortal(portal);
+    this._toggleScrollableContentClass();
+    return viewRef;
   }
 
   /** Moves the focus inside the focus trap. */
@@ -196,4 +206,19 @@ export class MatDialogContainer extends BasePortalOutlet {
     // view container is using OnPush change detection.
     this._changeDetectorRef.markForCheck();
   }
+
+  /**
+   * Toggles a class on the host element, depending on whether it has
+   * scrollable content. Used to activate particular flexbox styling.
+   */
+  private _toggleScrollableContentClass() {
+    const element: HTMLElement = this._elementRef.nativeElement;
+    const cssClass = 'mat-dialog-container-scrollable';
+
+    if (element.querySelector('.mat-dialog-content')) {
+      element.classList.add(cssClass);
+    } else {
+      element.classList.remove(cssClass);
+    }
+  }
 }

src/lib/dialog/dialog.scss

@@ -4,10 +4,13 @@
 
 
 $mat-dialog-padding: 24px !default;
+$mat-dialog-title-padding: 24px !default;
 $mat-dialog-border-radius: 2px !default;
-$mat-dialog-max-height: 65vh !default;
 $mat-dialog-button-margin: 8px !default;
 
+// TODO(crisbeto): not used anywhere, to be removed next major release.
+$mat-dialog-max-height: 65vh !default;
+
 .mat-dialog-container {
   @include mat-elevation(24);
 
@@ -32,27 +35,58 @@ $mat-dialog-button-margin: 8px !default;
   }
 }
 
+.mat-dialog-container-scrollable {
+  padding: 0;
+
+  // Since there are 5-6 levels of elements down before we can reach
+  // the projected content, we have to use a class that lets us propagate
+  // the dimensions down to the relevant flexboxes, in order for IE to
+  // work correctly.
+  &, .mat-dialog-component-host {
+    width: inherit;
+    min-width: inherit;
+    max-width: inherit;
+    height: inherit;
+    min-height: inherit;
+    max-height: inherit;
+    display: flex;
+    flex-direction: column;
+    overflow: auto;
+  }
+}
+
+.mat-dialog-title {
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  width: 100%;
+  flex-shrink: 0;
+  margin: 0;
+  padding: $mat-dialog-title-padding;
+  box-sizing: border-box;
+}
+
 .mat-dialog-content {
   display: block;
-  margin: 0 $mat-dialog-padding * -1;
-  padding: 0 $mat-dialog-padding;
-  max-height: $mat-dialog-max-height;
+  padding: $mat-dialog-padding $mat-dialog-padding 0;
   overflow: auto;
   -webkit-overflow-scrolling: touch;
-}
 
-.mat-dialog-title {
-  margin: 0 0 20px;
-  display: block;
+  // Avoid stacking the padding if there's a title.
+  .mat-dialog-title ~ & {
+    padding-top: 0;
+  }
 }
 
 .mat-dialog-actions {
-  padding: $mat-dialog-padding / 2 0;
+  padding: $mat-dialog-padding / 2 $mat-dialog-padding;
   display: flex;
   flex-wrap: wrap;
 
   // Pull the actions down to avoid their padding stacking with the dialog's padding.
   margin-bottom: -$mat-dialog-padding;
+  align-items: center;
+  flex-shrink: 0;
 
   &[align='end'] {
     justify-content: flex-end;

src/lib/dialog/dialog.spec.ts

@@ -1022,6 +1022,13 @@ describe('MatDialog', () => {
       }));
 
       runContentElementTests();
+
+      it('should set the `mat-dialog-component-host` class on the rendered component', () => {
+        const container = overlayContainerElement.querySelector('mat-dialog-container')!;
+        const host = container.querySelector('content-element-dialog')!;
+
+        expect(host.classList).toContain('mat-dialog-component-host');
+      });
     });
 
     describe('inside template portal', () => {
@@ -1093,6 +1100,11 @@ describe('MatDialog', () => {
         expect(container.getAttribute('aria-labelledby'))
             .toBe(title.id, 'Expected the aria-labelledby to match the title id.');
       }));
+
+      it('should set the `mat-dialog-container-scrollable` class on the container', () => {
+        const container = overlayContainerElement.querySelector('mat-dialog-container')!;
+        expect(container.classList).toContain('mat-dialog-container-scrollable');
+      });
     }
   });
 
@@ -1343,6 +1355,7 @@ class PizzaMsg {
 }
 
 @Component({
+  selector: 'content-element-dialog',
   template: `
     <h1 mat-dialog-title>This is the title</h1>
     <mat-dialog-content>Lorem ipsum dolor sit amet.</mat-dialog-content>
@@ -1360,6 +1373,7 @@ class PizzaMsg {
 class ContentElementDialog {}
 
 @Component({
+  selector: 'content-element-dialog',
   template: `
     <ng-template>
       <h1 mat-dialog-title>This is the title</h1>